CN115587399A - BIM-based project schedule management system and its application - Google Patents

Abstract

The invention relates to a project progress management system and application based on BIM, wherein a data model is generated by combining a three-dimensional data model expression method and a method for carrying out shielding inquiry with a plurality of viewpoints to identify hidden pieces in an assembly body, a progress management model establishes a real-time model and generates a corresponding calculation model according to the analysis of a data model structure, and a comparison model superposes and compares the real-time model with a plan model to provide a scheme for deviation correction and adjustment of construction progress. The invention needs to continuously adjust the target in the project process and adopts proper measures to solve the problems, the project often has the phenomenon that the completion time, the total cost or the resource distribution deviates from the original planned track, corresponding measures need to be adopted to lead the project development to be consistent with the plan, if the project has larger change or seriously deviates from the project process, the project schedule needs to be rearranged, the target plan is determined, the resource distribution and the budget cost are adjusted, thereby realizing the schedule balance.

Description

BIM-based project schedule management system and its application

technical field

The invention relates to the field of management systems, in particular to a BIM-based project progress management system and its application.

Background technique

The national grid infrastructure requires solid promotion of the standardized application of 3D design in construction management, construction organization, and file transfer, and the establishment of an information transmission and data sharing model based on 3D design applications to meet the management requirements of each stage of project construction. Explore the use of 3D design results Carry out standardized management of the process, and the traditional construction planning and progress management methods are gradually difficult to meet the existing business needs, mainly in the lack of visual and intuitive simulation methods for the remote control and control of the construction site progress by the owner and the construction management party;

Foreign research on 4D simulation of engineering progress is mainly based on the application of BIM technology. Exploring how to add time dimension to the 3D building model to realize 4D simulation of engineering progress is an important aspect of the application of foreign BIM technology in progress management.

The existing technology has the following deficiencies: the existing management system still has many limitations. First, the system mainly focuses on the dynamic management of the progress of the project construction stage, and does not involve other engineering stages such as engineering design. Second, the 3D composite model established by the system is only a simulation of the image and size of the building product, and does not include other building product information. It is not a real building information integration model, so a BIM-based project schedule is required. The management system solves the above problems.

Contents of the invention

The technical problem to be solved by the present invention is to provide a BIM-based project progress management system for the deficiencies of the above-mentioned prior art, and the system includes a data model, a progress management model and a comparison model;

The data model is generated by combining the three-dimensional data model expression method and the method of occlusion query from multiple viewpoints to identify hidden parts in the assembly. The progress management model is based on the analysis of the data model structure to establish a real-time model and generate a corresponding calculation model. The comparison model will be The real-time model and the planned model are superimposed and compared to provide a solution for the correction and adjustment of the construction progress.

Preferably, the data model includes a three-dimensional information model of the power grid, and the three-dimensional information model of the power grid is converted into a surface model by scanning the entity, and the specific steps are:

Let the points before scanning be A(XA, YA, ZA), B(XB, YB, ZB)...K(Xk, Yk, Zk), scan vector V(XV, YV, ZV), for these points along An, Bn...Kn are obtained after the scanning vector V scans the surface, and the line-surface network formed by these points is the boundary model of 3DGIS:

An=A+V, Bn=B+V... Kn=K+V

For curve scanning, select the curve Curve=(M1(X1, Y1, Z1), M2(X2, Y2, Z2)...Mn(Xn, Yn, Zn)) and change the tangent vector of the curve to Hn=Xn-Xn- 1, Yn-Yn-1, Zn-Zn-1, if there is a point A' scanned by A (XA, YA, ZA, 0), it is calculated by the following formula, where N is the surface normal:

By analogy, the conversion from the solid model to the boundary model is realized.

Preferably, the three-dimensional data model includes a solid model and a mesh model, wherein the solid model is used to describe the geometric and topological information of the component, and the mesh model uses polygonal patches to form the geometric shape of the object.

Preferably, the method for performing occlusion query from multiple viewpoints to identify hidden parts in an assembly includes the following steps:

(1) Generate a query object ID for the object to be queried;

(2) start occlusion query;

(3) Render objects that need to be occluded and queried;

(4) End the occlusion query;

(5) Extract the number of samples that are queried by occlusion;

(6) Delete the query object ID and recycle resources.

Preferably, in the recognition algorithm of hidden parts, the calculated visibility value of parts at a certain viewpoint is:

Where: λ ₁ +λ ₂ +λ ₃ =1;

Among them, λ ₁ , λ ₂ and λ ₃ are weights, and the initial setting of part visibility rate, part area contribution rate and part volume contribution rate occupies the same weight, that is, λ ₁ , λ ₂ and λ ₃ are all 1/3;

定义临界参数F_T(0<F_T<1)，装配体中的某个零部件的F值大于临界参数时，装配体的外部进行观察零部件可见，否则零部件为隐藏件。After part i completes the occlusion query at all set viewpoints, the maximum visibility value of part i is obtained, namely

Define the critical parameter F _T (0<F _T <1). When the F value of a component in the assembly is greater than the critical parameter, the component is visible from the outside of the assembly, otherwise the component is hidden.

Preferably, the recognition algorithm of the hidden parts jointly evaluates the priority value C(v) of the vertex through the position of the vertex in the cache and the degree of the vertex, and the priority value C(R) of the triangle ring is the value of all unoutput triangles in the ring sum of vertex priority values

The vertex priority value C(v) can be calculated by the following formula:

C(v)＝ _Cp (v)+ _Ca (v)

in,

In the above formula, p represents the position of vertex v in the cache, s represents the size of the cache space, a represents the number of unoutput triangles adjacent to vertex v, k ₁ , k ₂ , and k ₃ are coefficients.

Preferably, the model graphic element data structure of the three-dimensional information model of the power grid includes basic data and extended data, wherein the basic data includes geometric data, physical data and functional data, and the extended data includes technical data, economic data and management data.

Preferably, the real-time model includes the statistical distribution of the duration of the process, the statistical distribution includes normal distribution, beta distribution, uniform distribution and triangular distribution, in the normal distribution, the mean value, median and mode of the duration of the process Coincidence, the probability that the duration of the process is greater than or less than the average value is equal, and the probability of the process being delayed or advanced is equal. In the Beta distribution, the distribution range is in [0, 1]. The distribution formula of the Beta distribution is as follows:

(1) mean value:

(2) Variance:

The value range of α and β is 0:0.1:10000, and the value range of the mean value is 0.3:0.05:0.5. The simulation results are stored in the matrix respectively. The first column is the α value, the second column is the β value, and the third column is the β value. are listed as variance values.

Preferably, in the said Beta distribution, the safety time is taken as the difference between the duration of the process under the 95% completion probability and the duration under the 50% completion probability of the process, and the formula is as follows:

T _k ＝[F(x)I _x＝0.95 -F(x)I _x＝0.5 ]×t _k

In the formula, F(x) is the distribution function of Beta distribution, T _k is the safety time of process k, and t _k is the duration of process k.

The present invention also provides an application of a BIM-based project progress management system. The progress management system is applied to substation construction simulation project management. Based on the D3Station platform, the analysis and visualization of the model can be realized, and the attributes of the model can be viewed.

Compared with the prior art, the beneficial effects of the present invention are:

1. The present invention analyzes the characteristics of the GIM three-dimensional product model and the data expression methods of the existing three-dimensional models, and proposes a three-dimensional data model expression method that can be quickly displayed on desktop devices for the characteristics of mobile devices. This data model has the advantages of fast drawing speed and memory saving, which meets the needs of efficient browsing on the desktop platform, and the security of the model is also guaranteed. In addition, the data model contains complete geometric information, product structure information and attributes, which meets the needs of users in Requirements in engineering practice; the data model with small file volume of the present invention filters non-geometric information such as parameters and PMI in the original model, and the separation of assembly files and part files avoids repeated expressions of the same model, and rational organization of geometric data Measures such as compression have greatly reduced the amount of model data, and the efficiency of transferring models through mobile networks has been greatly improved compared with the original model, which is also conducive to storing more 3D models on mobile devices;

2. The fast reading data model fully considers the characteristics of the hardware of the mobile device and the 3D graphics rendering system. In the data model generation stage, the data is reasonably organized and displayed, and the time-consuming optimization operation is transferred to the calculation Execute on desktop computers with stronger capabilities, avoiding the weakness of some desktop devices with lower hardware performance, the generated data model can make full use of the performance of mobile terminals, speed up the loading and drawing speed, and enable demonstration and interaction on low-performance mobile devices 3D models are possible;

3. The generation method of the data model is given, and the lightweight algorithm is studied, and a method of occlusion query from multiple viewpoints to identify hidden parts in the assembly is proposed, which can automatically judge the assembly The invisible parts inside the model and the subtle parts that have little influence on the appearance, combined with the lightweight expression method, can reduce the number of drawing elements and improve the drawing efficiency without destroying the product structure relationship. In addition, it also proposes A linear time vertex cache optimization algorithm, which uses effective heuristic search rules, can still obtain a good cache optimization effect in the case of unknown cache parameters, and can effectively speed up the display speed of the data model;

4. Through the comparative analysis between the actual progress and the project plan, many deviations can be found, and potential problems in the project can be pointed out. In order to avoid the problems caused by the deviation, it is necessary to continuously adjust the goals during the project process and take appropriate measures To solve the problems that arise, the completion time, total cost or resource allocation of the project often deviates from the original planned track, and corresponding measures need to be taken to make the project development and plan tend to be consistent. If the project undergoes major changes or seriously deviates from the project process, then It is necessary to re-arrange the project schedule and determine the target plan, adjust resource allocation and budget expenses, so as to achieve schedule balance.

Description of drawings

Fig. 1 is a schematic diagram of the technical route of the present invention.

Fig. 2 is a data structure diagram of the grid information model of the present invention.

Fig. 3 is a data structure diagram of the data model of the present invention.

Fig. 4 is a flow chart of generating the data model of the present invention.

FIG. 5 is a statistical diagram of the occlusion query results of the present invention.

Fig. 6 is a flow chart of the identification of hidden parts of the present invention.

Figure 7 is a simplified schematic diagram of the engine model of the present invention.

Fig. 8 is a schematic diagram of a triangle sequence in the present invention.

FIG. 9 is a flow chart of cache optimization in the present invention.

Fig. 10 is a data structure diagram of a model graphic element of the present invention.

Fig. 11 is a system architecture diagram based on MVC in the present invention.

Fig. 12 is a flowchart of the realization of the MVC-based system architecture of the present invention.

Fig. 13 is a system diagram of the BIM-based progress management application framework of the present invention.

Fig. 14 is an overall framework diagram of the BIM information platform of the present invention.

Fig. 15 is a schematic diagram of 4D simulation analysis of the schedule of the present invention.

Fig. 16 is an analysis diagram of the operation sequence of the network diagram of the present invention.

Fig. 17 is a progress monitoring view of the present invention.

Fig. 18 is a comparison diagram between the planned progress model and the actual progress model of the present invention.

Fig. 19 is a block diagram of the substation 4D construction progress management platform of the present invention.

detailed description

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments It is a part of embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

It should be noted that when an element is referred to as being “fixed” to another element, it can be directly on the other element or there can also be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or intervening elements may also be present.

Example 1

Please refer to Fig. 1, the BIM-based project progress management system described in this embodiment, the system includes a data model, a progress management model and a comparison model, wherein,

Data model: Combining the advantages of entity model and grid model, it fully considers the needs of low-performance desktops. Generally speaking, it has the following characteristics and advantages:

(1) Small file size The data model filters non-geometric information such as parameters and PMI in the original model. The separation of assembly files and part files avoids repeated expressions of the same model. Measures such as reasonable organization and compression of geometric data make the model The amount of data is greatly reduced, and the efficiency of transferring the model through the mobile network is greatly improved compared with the original model, which is also conducive to storing more 3D models on the mobile device;

(2) The fast reading data model fully considers the hardware of the mobile device and the characteristics of the 3D graphics rendering system. In the data model generation stage, the data is reasonably organized and displayed, and the time-consuming optimization operation is transferred to Executed on desktop computers with stronger computing power, avoiding the weakness of some desktop devices with low hardware performance, the generated data model can make full use of the performance of mobile terminals, speed up the loading and drawing speed, and enable low-performance mobile devices to demonstrate and Interactive 3D models become possible;

(3) Saving the use of memory references allows only one copy of the same part to be saved in the memory, and the others are obtained through the space transformation matrix, which can greatly reduce memory usage and meet the more stringent requirements of 3D applications for memory;

(4) Complete model information The data model has complete geometric information and product structure information, which has high usability and meets the requirements for the use of 3D models in the mobile network environment;

(5) Guaranteed data security The data model does not contain information such as the characteristic parameters and modeling parameters of the model, and the model cannot be edited again, which can ensure that the data model will not be used for other purposes such as reverse engineering.

Firstly, the characteristics of the GIM 3D product model and the data expression methods of the existing 3D models are analyzed. Aiming at the characteristics of mobile devices, a 3D data model expression method that can be quickly displayed on desktop devices is proposed. This data model It has the advantages of fast drawing speed and memory saving, which meets the needs of efficient browsing on the desktop platform, and the security of the model is also guaranteed. In addition, the data model contains complete geometric information, product structure information and attributes, which meets the needs of users in engineering practice. needs;

Secondly, the generation method of the data model is given, and the lightweight algorithm is studied, and a method of occlusion query from multiple viewpoints to identify hidden parts in the assembly is proposed, which can automatically determine the assembly model Invisible internal parts and subtle parts that have little impact on the appearance, combined with lightweight expression methods, can reduce the number of drawing elements and improve drawing efficiency without destroying the product structure relationship. In addition, a A linear time vertex cache optimization algorithm, which uses effective heuristic search rules, can still obtain a good cache optimization effect in the case of unknown cache parameters, and can effectively speed up the display speed of the data model.

Progress management model: By analyzing the content of project progress management and common progress management techniques, explore the establishment of three-dimensional power grid information model and construction progress data, analyze the establishment of four-dimensional power grid information model, and propose the realization of the integration of BIM data and construction progress In this way, combined with the analysis of system functional requirements and 3D model data structure, the structural system of BIM4D system is formed, and its realization process is designed.

Comparison model: systematically discusses the process of collecting progress information on the construction site and the method of superimposing and comparing the real-time model and the planned model, and then provides solutions for the correction and adjustment of the construction progress, and solves the problem of combining the real-time model and the platform of the construction site The plan model of the related information is compared in the specific way. The specific method is to use the camera to collect the construction site information, and reconstruct the construction site model through image registration, feature point matching, motion structure, model registration and other technologies, and overlap with the plan model. Provide a real-time data basis for the output of subsequent progress reports and three-dimensional progress display;

After updating the actual progress information in the system, through the comparative analysis between the actual progress and the project plan, many deviations can be found, and potential problems in the project can be pointed out. In order to avoid problems caused by deviations, constant adjustments are required during the project process Goals, and take appropriate measures to solve the problems that arise. Projects often have a phenomenon that the completion time, total cost or resource allocation deviates from the original planned track. Corresponding measures need to be taken to make the project development and plan tend to be consistent. If there are major changes in the project Or seriously deviate from the project progress, it is necessary to re-arrange the project schedule and determine the target plan, adjust resource allocation and budget expenses, so as to achieve progress balance.

Example 2

Please refer to Figure 2. In the data model, the main idea is to study the data organization structure of the general model, product model, and power transmission and transformation project, extract the commonality of the data, and form a data analysis plan for the power grid information model. According to the company's 3D design standards, establish Detect indicators, test the integrity and correctness of data format and content, and finally study the efficient processing and storage of power grid information model data, refer to the organization method of geographic information data, study the pyramid scheme according to the display scale and data fineness, and combine the data composition structure Study the LOD strategy, simulate the data falling from high altitude to observe the process of objects from blurring to clear, start from the amount of data, study the simplification scheme of data geometric texture, and optimize data storage under the premise of ensuring data clarity;

As shown in Figure 3, the most important factor affecting the technical framework of the integration of the grid information model (GIM) and GIS is often the data format. Since the grid information model and GIS data have their own data formats, these multi-source heterogeneous data How the format is compatible on a platform becomes a key issue;

Data format conversion is currently the mainstream way of integrating GIS and 3D models. Most of the research on data format conversion focuses on the conversion from IFC to CityGML, and some studies focus on the conversion from CityGML to IFC, from power grid information model data to GIS data. Transformation is the process of refining data for coarse processing. Analyzing the power grid information model includes two aspects: geometry and semantics:

1) Multi-level geometric information extraction and conversion

Most of the three-dimensional information models of the power grid are solid geometry construction method (CGS), while most of the GIS expression formats are surface boundary methods, so geometric information conversion is required. The conversion from an entity to a surface model requires the use of scanning methods. After scanning, it is necessary to Carry out triangular grid division on the scanned model to obtain the surface model of 3DGIS;

The scanning of the straight line is relatively simple. Let the points before scanning be A(XA, YA, ZA), B(XB, YB, ZB)... K(Xk, Yk, Zk), and the scanning vector V(XV, YV, ZV), scan these points along the scanning vector V to get An, Bn...Kn, the line-surface network formed by these points is the boundary model of 3DGIS:

An=A+V, Bn=B+V... Kn=K+V

For the scanning of the curve, we choose the curve Curve=(M1(X1, Y1, Z1), M2(X2, Y2, Z2)...Mn(Xn, Yn, Zn)) to change the tangent vector of the curve to Hn=Xn-Xn -1, Yn-Yn-1, Zn-Zn-1, if there is a point A' after scanning by A(XA, YA, ZA, 0), it is calculated by the following formula, where N is the surface normal:

By analogy, the conversion from the solid model to the boundary model can be realized;

2) Mapping of semantic information

In addition to pure geometric information conversion, the mapping of semantic information is also an important part of the integration of GIM and GIS. Simple data format conversion does not realize the integration of GIM and GIS. The structure of the model has changed but the semantics of the model have not changed;

The first is the difference in the form of geometric expression. There are three forms of expression in the power grid information model, such as boundary description, scanning volume formed by extension or rotation, and structural solid geometry, while the data standard supported by the GIS platform only has one geometric expression form of boundary description. After the GIM model is converted into a format supported by the GIS platform, the geometric information expressed by the scanning volume formed by stretching or rotating and the method of constructing solid geometry can only be expressed by the boundary description method, which requires a large amount of coordinate data to express multiple meshes information, which will inevitably lead to the loss of geometric information and the increase of data volume. On the other hand, there is a difference in object semantics. Since the grid information model and 3DGIS have different expressions and understandings of spatial objects, there is no related standardization research on object semantics. Therefore, in the process of transforming the GIM model to the data format supported by GIS, the loss of semantic information is inevitable, so it is also necessary to reconstruct the geometric semantics of the power grid information model to the 3DGIS model;

The power grid information model has rich semantics, and the mapping can often be found in the 3DGISLOD4 hierarchical model. The semantic information of the LOD3-LOD0 level is gradually reduced. Therefore, semantic filtering is required during the conversion process to abstract and filter some information. Just download useful information, associate the semantic information and geometric information of each component with a unique ID value, and provide index information for the management of model data;

3) Spatial scale change

After triangulating the GIM solid model into a GIS-supported triangulation model, since GIM uses a local coordinate system, when the model is imported into the 3D-GIS system, it is necessary to use the coordinates of the model measurement points and the actual measurement points to establish positioning reference information. Obtain the coordinate conversion matrix of the model family, convert the local coordinate system to the global coordinate system, and complete the correct positioning of the model in the 3D-GIS system coordinate system. The three commonly used models for conversion in different coordinate systems are the Bursa seven-parameter model , Molodinsky model, Wuce model;

In order to solve the problem of fast viewing of 3D product models on mobile devices with limited performance and resources, and enrich the channels for users to exchange product data, it is necessary to use desktop computers to perform lightweight processing on the original model to obtain data models for direct browsing by mobile devices;

Starting from the problems existing in the current 3D model data sharing, the characteristics of the 3D product model and the shortcomings of the existing model expression methods are analyzed, and a data model expression method that can be quickly displayed on mobile devices is proposed. The 3D model expression method Generally speaking, it can be divided into two categories, one is the solid model, and the other is the grid model, as follows;

1) Solid model: The solid model can be divided into three categories: Boundary Representation (B-Rep, Boundary Representation), Construction Solid Geometry (CSG, ConstructionSolidGeometry) and scanning method. Most 3D systems (Pro/E, UG, Catia, Inventor, etc.) are all solid models;

The solid model can describe the geometric and topological information of the part extremely accurately. However, the solid model has the following problems, which limit its application in data sharing:

(1) The solid model does not contain any triangular patch information. It usually requires a lot of calculations to discretize it into a polygonal mesh before displaying it, so the loading time is long. For complex 3D product models, it takes a long time to load Displaying the time is even more unacceptable;

(2) The data structure of the physical model is complex and the file size is huge. The information in it is oriented to various purposes. For users, much of the information is redundant information. For example, proofreaders and reviewers mainly use the model to browse and circle , they only pay attention to the structural geometric information of the part, the analysis engineer only needs to use the simplified product geometric information in the analysis process, and the remote customer only needs geometric information to browse the appearance shape of the model;

(3) The same 3D system or common 3D browsing software as the modeler must be used to browse the solid model, and the general 3D browsing software is usually developed by a third party, which generally has problems such as lag and insufficient stability, and the diversity of 3D systems , leading to the heterogeneity of 3D product data, affecting data sharing and communication within and between enterprises, and reducing production efficiency;

(4) The confidentiality of the physical model is poor, which contains sensitive design information such as the modeling process and characteristic parameters. Once it is used for purposes other than collaborative development, such as reverse engineering, it will cause heavy losses to the enterprise;

2) Grid model: The grid model is an inaccurate model expression method that uses a large number of polygonal patches to approximate the geometric shape of the object. There are many file formats for the grid model, such as STL, VRML, PLY, OBJ, etc. The most common one is the STL file format launched and promoted by 3DSystems. The STL grid model has been widely used in the manufacturing industry. Most of the 3D systems can output the model file in the STL format. The geometric shape of the model is described in the form of . Each triangle patch records the normal vector of the triangle and the position coordinates of the vertices of the triangle. There are two storage formats for the STL mesh model, ASCII and binary. The file structure of the ASCII format is as follows:

Nx, Ny, and Nz in the file represent the components of the normal vector of the triangle surface in the three directions of xyz, V _1x , V _1y , and V _1z represent the coordinate values of the vertices in the xyz direction, and the rest are the keys in the file Character;

From the above STL example, it can be seen that the data structure of the mesh model is simple, and the expression method of the triangular surface enables it to use the hardware to accelerate the rendering process to achieve the purpose of quickly displaying the 3D model, but the mesh model has the following problems:

(1) The grid model only contains the display information of the object, without the assembly structure relationship of the model, cannot express the relationship between parts, and also lacks key information such as attributes, which is difficult to meet the actual requirements of the project;

(2) The grid model is generally not compressed or the compression ratio is not high, and the data volume is large, which is not conducive to the network transmission and storage of the model;

Due to the above-mentioned deficiencies in the traditional 3D model when transmitting information, it is necessary to extract the geometric information of the 3D product model, compress and optimize it, and simplify the extraction of the required attribute information and product structure information, so as to obtain A data model that is small in scale, high in efficiency, and easy to browse quickly. The following will introduce the expression method of this data model;

The data model is mainly used for quick browsing and interaction of desktop devices. Therefore, the design of the data model information storage and expression mechanism must fully consider the characteristics of the desktop device itself and the optimization strategy for the performance bottleneck of the desktop graphics system. In order to make the 3D product model Lightweight can meet the needs of desktop users, and the generated data model must meet the following conditions:

(1) The data model must first ensure the browsing experience on the desktop device. Due to the embedded architecture, the hardware resources and performance of the desktop device cannot be compared with the desktop computer. Its computing and graphics rendering capabilities are relatively limited. In order to ensure a good browsing experience Experience, the model must have a fast display speed and be able to meet the needs of real-time interaction. The data model file should be reasonably organized and not too complicated. Under the premise of ensuring the display speed, performance such as compression ratio can be appropriately sacrificed, and certain Optimization measures that do not rely on the latest hardware support to ensure that complex models can have a smoother experience on various desktop devices;

(2) The data model needs to ensure its usability in the engineering field. The lightweight process generally simplifies and compresses the geometric information of the product model, and simplifies and extracts information such as dimensions, attributes, fits, and parameters. The data generated through this process The model will lose part of the information, but this process must not destroy the usability of the model. Specifically, in terms of geometric appearance, it is not allowed to produce overhanging edges, overhanging surfaces, and holes, and key features must be preserved. In terms of non-geometric information, due to the screen Due to the limitation of size and interaction mode, 3D applications on desktop devices are mainly display-oriented, so the modeling process, engineering constraints, features and other information can be simplified or exist as optional items, but the assembly and product structure must be extracted information, otherwise the data model will lose its role in data sharing in the engineering field;

(3) The data model needs to have a smaller file size. Due to the limitations of the embedded system architecture of desktop devices, its storage and memory capacity are small, and it is difficult to expand. Therefore, it is very necessary to reduce the size of the model. On the one hand, it is beneficial to Transferring models through the network can also save memory, making it possible to demonstrate data on low-performance desktop devices;

According to the above requirements, the following design scheme of the 3D data model file is proposed:

(1) For each part, organize the triangular mesh data of the same color together, perform geometric compression on it, and save it as a separate file, and organize the data according to the color instead of the surface as the basic unit, which can maximize the Guarantee the maximization of one-time incoming data, and also reduce the complexity of the shader and the state changes during the rendering process. Only one color value needs to be recorded in the color list, which not only reduces data redundancy, but also optimizes The role of the rendering pipeline;

(2) Use XML (ExtensibleMarkupLanguage) format to describe model product structure and attribute data. XML has good scalability and platform independence, and can realize the separation of content and form, which is very suitable for describing structurally strong assembly In addition, the XML expression method enables the loading process to use the SAX method to parse the model files sequentially, and the SAX parsing method does not need to save the entire document in memory, so it is very suitable for mobile devices with limited memory resources;

(3) Use references to reduce redundancy. There are usually many parts with the same shape in the 3D product model. Data redundancy can be avoided through references, thereby reducing the volume of lightweight files and reducing memory usage;

(4) Manage data in the form of containers. In lightweight files, all data is included in different container nodes. Lightweight assembly files point to geometric data files of parts through containers, which is conducive to data expansion and modification;

(5) Using Levels of Detail (LOD) technology, adding multi-resolution representations of parts to the geometric data, using the bounding box of the part to support the LOD model of the part, the bounding box of the part corresponds to the rough model, while the actual part model Corresponding to the accurate model, by sacrificing the display quality, the drawing time of the model can be reduced, which is convenient for users to quickly browse and interact with the 3D model;

(6) Accelerate the display of geometric data. The display acceleration is mainly reflected in two aspects. On the one hand, the visibility of parts is pre-judged in lightweight, and the visibility of parts is recorded in the assembly file. When drawing the model, it can be based on The pre-provided visibility information prevents invisible and subtle components from entering the rendering pipeline, and can also be displayed manually when needed, achieving a good balance between drawing speed and usability. The grid data is optimized for the vertex cache. By modifying the triangle sequence of the grid, the vertex cache hit rate during the rendering process is improved, and the display speed of the data model is accelerated;

Please refer to Figure 4, the data model file adopts a multi-document structure, the assembly file and the part file are stored separately, the assembly file records the product structure and attribute information, and the part file records the optimized display information;

The assembly file records the relevant information of the sub-assembly and parts, including component names, relative paths of sub-components, visibility of components, relative transformation matrix, geometric display properties, etc., combined with the geometric information of parts, the product model can be developed The fast display and interaction of the assembly file extracts the attribute information in the original model, including physical attributes such as product weight, area, volume, and weight unit, as well as similar user-defined attributes such as product code and stage marks. In addition, The name, format and relative path of the model thumbnail are recorded in the assembly file. The existence of the thumbnail allows the user to get a general understanding of the model information without opening the model file, avoiding a lot of time-consuming loading of complex models. Assembly There is no geometric information in the volume file, and its data volume is not large, so the file size can be kept small;

The part file is used to record the display information of the part in its own object coordinate system, including triangular mesh data for quick display and point and edge information for representing contour points and contour edges, because most models use surface coloring , the report organizes the grid data by color. When multiple faces have the same color, only one color value needs to be recorded in the color list. The grid data is first optimized by the vertex cache, and then stored by index, that is, the part display information It is saved as a unique vertex and a triangle sequence arranged by vertex index. For a 3D product model, its topological relationship is more complicated. At the same time, considering the low computing performance of mobile devices, the model is not topologically compressed in the part file. Geometry compression only to reduce vertex data precision;

When viewing the data model file, the user can first judge whether it is the model you want to browse with the help of the thumbnail, and then choose whether to open the model file. The loading of the data model file first traverses from the total product structure to get all lightweight Sub-assemblies and parts, and then build the entire scene and draw it. In the lightweight assembly file, the matrix of all parts is the transformation matrix relative to the position of the upper-level parts, so the transformation matrix of all the upper-level nodes of the part is the same The absolute position of the part in the general assembly can be obtained by multiplying it. During the display process of the file, the parts whose visibility attribute is marked as invisible can be cut off at the beginning, and will not be sent to the rendering pipeline. When you need to view the assembly Only when the internal structure of the body, this part of the geometric data is sent to the rendering pipeline for rendering;

The main bottleneck of 3D graphics rendering on the current platform is the contradiction between the huge amount of model data and the limited hardware performance of the terminal. Model simplification and model data layout optimization are two feasible methods to solve this bottleneck. Simplifying the model can Reduce the amount of primitive data that needs to be drawn, optimize the data layout of the model can increase the reuse rate of the hardware cache, and achieve the purpose of display acceleration. For this purpose, a hidden part recognition algorithm for assemblies is proposed, and lightweight expression The combination of methods can simplify some parts in the assembly and reduce the workload of drawing. In addition, in order to improve the vertex cache hit rate, this chapter studies the triangle arrangement of the mesh model and proposes a new vertex cache optimization algorithm. Both of these optimization operations are performed on desktop computers, enabling low-performance devices to efficiently browse the data model;

In the complex 3D product model, the number of component models is huge, the hierarchical structure is deep, the structural relationship is complex, and the display speed is slow. In order to meet the needs of quickly browsing the 3D product model on different hardware, a multi-level data model expression method is proposed. , the data model needs to extract geometry, topology and corresponding assembly information from the original model and organize it reasonably. Therefore, using the secondary development tools provided by common 3D systems to develop the corresponding data model export interface program can meet the needs according to the actual project. The effect, efficiency and flexibility are relatively high, and these development tools are backward compatible, so the stability of the export interface program is relatively good, and no frequent changes are required;

Please refer to Figure 5. The lightweight process inputs 3D product models in various file formats. After the following lightweight operations on the desktop computer, a data model that can be quickly displayed directly on the terminal desktop device can be obtained;

1) Extraction of product structure and attribute information, extracting non-geometric information such as the product structure of all parts of the assembly, the name and attribute information of the parts, and the transformation matrix of each part relative to the upper-level assembly. The structure of the assembly is An obvious tree structure, in the information extraction process, you can use the recursive method to obtain the required information, when the type of the model is an assembly, extract the information and perform the next recursive operation, if it is a part, after the information extraction is completed After exiting the recursion, only with the structure and attribute information can the accurate display of the data model and attribute query be performed in an environment separated from the 3D system;

2) Triangulation of geometric data, triangulation is performed for each part in the assembly, and a triangular mesh that supports fast display is obtained;

3) Key geometric information extraction, extracting key edge and point information in the model to support some special display requirements;

4) Hidden part identification and recording, occlusion query for the entire assembly model from multiple viewpoints, pre-judging the visibility of parts through multiple results, and recording the results in the lightweight assembly file, this part will be in the next section for a detailed introduction;

5) Vertex cache optimization. This step modifies the triangle sequence of the 3D model to increase the vertex cache hit rate, reduce memory bandwidth requirements, and speed up the drawing speed of the model. This will be described in detail below;

6) Encoding compression, through the three steps of quantizing the vertex position, prediction and entropy encoding, the geometric information of the part file is geometrically encoded. In addition, the file is stored in binary mode, and the assembly file is compressed using Huffiman encoding;

Due to the large number of parts and components contained in the 3D product model, its structural relationship is also very complicated. In the entire assembly, there are generally invisible parts inside the model and subtle parts that have little influence on the appearance. Here It is commonly referred to as hidden parts. According to the analysis in Chapter 2, in order to realize the rapid drawing of 3D models on desktop terminal devices, hidden parts in the assembly can be eliminated to reduce the number of primitives sent to the drawing pipeline. Therefore, in the data model export During the process, an automatic way is needed to judge the visibility of the part, to obtain whether the part is a hidden part, and to record its visibility in the generated lightweight assembly file. When the data model is displayed, you can choose not to Draw hidden parts, and display them manually if necessary, which not only achieves the purpose of simplification but also retains the complete product structure of the model;

The basic idea of hidden parts identification is to perform occlusion query on the assembly from multiple viewpoints, obtain the visible area of the assembly itself and each component, and then combine all the query results and the volume information of the components to obtain all hidden components;

In order to judge the visibility of parts, use OpenGL's occlusion query technology to query the model to obtain the number of pixels that the model passes the depth test, and then decide whether to render the object according to the query results;

In order to use occlusion queries, the following steps need to be performed:

Step1: Generate a query object ID for the object to be queried;

Step2: start occlusion query;

Step3: Render objects that require occlusion query;

Step4: End the occlusion query;

Step5: Extract the number of samples that pass the occlusion query;

Step6: Delete the query object ID and recycle resources;

Using occlusion query technology can reduce the number of primitives that need to be drawn, and can greatly increase the frame rate of drawing. However, the overhead of executing occlusion query is very high, which is mainly manifested in two aspects. First, each query will add an additional drawing call. In addition, waiting for the query results will cause a large delay, which affects the performance of the CPU and GPU. Due to the limited hardware rendering capabilities of ordinary desktop devices, at the same time, the occlusion query is only supported from the OpenGLES3.0 standard. , so there are still great limitations in using this technology to accelerate the drawing of complex 3D graphics directly on ordinary desktop devices. However, the occlusion query function can be used to comprehensively analyze the data in the assembly from multiple viewpoints in the data organization stage of the data model. Visibility judgments are made in advance for all parts of the model. When drawing the model, it is possible to determine whether to draw and when to draw based on the visibility information, which is conducive to the quick browsing of the 3D model;

In order to fully understand the model, the user needs to observe the model from multiple angles. For this reason, multiple viewpoints are set to comprehensively judge whether the part is visible, so that the simplified 3D model can still correctly reflect the appearance of the part, satisfying For the purpose of 3D model data exchange, the viewpoint is evenly distributed on a sphere whose radius is three times the radius of the enclosing sphere of the assembly, so that the entire assembly is just inside the viewing cone, in order to achieve a more balanced algorithm complexity and result accuracy Effect, the number of viewpoints is set to 12, and the viewpoint direction is that the vertex points to the center of the 3D model enclosing sphere, and the occlusion query test is performed from these viewpoints to obtain the number of pixels on the screen after the parts are rendered, and comprehensively analyze the rendering results. Finally determine whether the component is a hidden part;

In order to describe the algorithm more clearly, the following variables are defined:

表示对装配体进行渲染时，在视点j处单独对零件i进行遮挡查询得到的其通过深度测试的像素数量；(1)

Indicates the number of pixels that pass the depth test obtained by performing an occlusion query on part i at viewpoint j when rendering the assembly;

表示单独对零件i进行渲染时，在视点j处对零件i进行遮挡查询得到的其通过深度测试的像素数量；(2)

Indicates the number of pixels that pass the depth test obtained by performing occlusion query on part i at viewpoint j when rendering part i alone;

表示对装配体进行渲染时，在视点j处对整个装配体进行遮挡查询得到的其通过深度测试的像素数量；(3)

Indicates the number of pixels that pass the depth test obtained from the occlusion query of the entire assembly at the viewpoint j when the assembly is rendered;

(4) V _i represents the volume of part i;

(5) V _T represents the volume of the entire assembly;

表示零件i在视点j的可见性值，用于衡量该零件是否可以认为是隐藏件；(6)

Indicates the visibility value of part i at viewpoint j, which is used to measure whether the part can be considered as a hidden part;

In the hidden part recognition algorithm, the visibility value of a component at a certain viewpoint is calculated by the following expression:

Where: λ ₁ +λ ₂ +λ ₃ =1;

In the above formula, λ ₁ , λ ₂ and λ ₃ are the weights. This expression can better identify the parts that are close to invisible and the subtle parts that do not affect the appearance of the assembly model. The initial setting of the part visibility rate, Part area contribution rate and part volume contribution rate have the same weight, that is, λ ₁ , λ ₂ and λ ₃ are all 1/3, and in actual operation, corresponding adjustments can be made according to the specific effect to obtain a more satisfactory effect;

根据实际需求定义一个临界参数F_T(0<F_T<1)，当装配体中的某个零部件的F值大于该临界参数时，则可以认为从装配体的外部进行观察该零部件是可见的，否则，认为该零部件为隐藏件；When part i completes the occlusion query at all set viewpoints, the maximum visibility value of the part can be obtained, namely

Define a critical parameter F _T (0<F _T <1) according to actual needs. When the F value of a component in the assembly is greater than the critical parameter, it can be considered that the component is viewed from the outside of the assembly. Visible, otherwise, the part is considered as a hidden part;

Please refer to Figure 6, for the assembly model, use the above-mentioned component visibility judgment algorithm to automatically identify the hidden parts in the assembly;

It should be noted that in the process of identifying hidden parts, the traversal of parts is a recursive process. When the selected parts are sub-assemblies, on the one hand, it is necessary to perform multi-view occlusion query tests on the sub-assembly as a whole, and at the same time It is necessary to read the subassembly model, treat the subassembly as a new whole and perform hidden parts identification to obtain the visibility information of the components in the subassembly;

For more complex 3D models, the cost of occlusion query is relatively high. In order to improve the recognition efficiency, the bounding box of the object can be used instead of the object for occlusion query. Box information, does not need to calculate the bounding box separately;

The input of this process is the grid model generated during the lightweight process. When the parts in the assembly have completed the hidden part identification work, the corresponding visibility information can be recorded in its lightweight assembly file;

Please refer to Figure 7, after simplifying the hidden parts of the assembly model, the number of primitives that need to be drawn can be reduced and the drawing speed can be accelerated;

The specific information of the engine model before and after simplification is shown in Table 1:

number of parts number of vertices Number of triangles original model 368 404422 424720 Simplified 152 317908 334655

Table 1

It can be seen from Table 1 that the number of parts in the engine has been greatly reduced after the identification and simplification of hidden parts, which has brought about a large reduction in the number of vertices and triangles in the model. Of course, the effect of this operation is closely related to the model itself. If the shape of the model is complex, the shape is closed, and there are many small parts, etc., the number of hidden parts identified will be more. On the contrary, the simplified model obtained cannot obtain obvious simplification effect, because most of the hidden parts identified as The parts are all inside the assembly or are small parts (such as bolts, nuts, etc.), so the appearance of the 3D model after removing the hidden parts has no obvious change. In addition, the lightweight assembly file only records the The visibility of parts does not remove these hidden parts from the product structure relationship. Therefore, all parts can be displayed when needed, without affecting the correct expression of the product structure of the assembly model, fully ensuring the data model the availability of

After simplification, there are still many parts inside the assembly. These parts cannot be observed from the outside, but they are not considered as hidden parts. There are also some smaller parts outside the assembly and are recognized. The reason for this phenomenon The main reason is that the proposed data model is a multi-level structure. The general assembly file only records the information of the sub-assembly and parts at the next level, while the sub-assembly is composed of which parts, the location of the part file and other information are all recorded. In sub-assembly files, this file information organization method can reduce data redundancy and also bring convenience to users. For example, for a 3D model of a car, if the user wants to view the engine part of the car, he only needs to open the The engine assembly file is enough, instead of loading the extremely complicated automobile general assembly file, in order to make any level of sub-assembly model meet the purpose of data exchange, in the process of identifying hidden parts, the parts must be targeted at the above The first-level assembly judges its visibility, and cannot only focus on whether it is visible in the general assembly, thus limiting the further improvement of the degree of simplification;

When rendering a 3D model, the graphics processing unit needs to read the vertex data of the model from the memory, but the memory bandwidth of the mobile device is limited, and it takes a long time to access the vertex data. In the process of quantization, the vertex cache hit rate of the GPU is improved by changing the sequence of model triangles, so that the generated data model has the effect of rendering optimization, and shortens the time consumed by the mobile device GPU to access vertex data during drawing;

In order to alleviate the gap between data processing speed and access speed in the graphics rendering process, people add a vertex cache (VertexCache) to the graphics processor. The vertex cache stores vertex data processed by transformation and lighting effects. If a vertex is not in the cache In the middle, it is necessary to read data from the system memory or GPU memory, and for the hit vertex buffer content, the data can be directly used in the next stage, avoiding repeated geometry processing, and can effectively reduce data reading The overhead of fetching is usually used by researchers to describe the vertex cache hit rate of the graphics processor using the average vertex mismatch rate (AverageCacheMissRatio, ACMR). ACMR is numerically equal to the average number of vertices that each triangle needs to read from memory when drawing a frame. , the lower the vertex mismatch rate, means that the number of times the graphics processing unit accesses the vertex data in the memory is less, and the time required for vertex reading and geometric transformation during the rendering of the 3D model is also less. The maximum value of the vertex mismatch rate is 3. That is, all the vertices of the model are not in the vertex cache. In the triangular mesh model, the number of triangular faces is close to twice the number of vertices, so the theoretical minimum value of the vertex mismatch rate is 0.5. Due to the complexity of the topological relationship and The limit of the size of the vertex buffer capacity, the theoretical minimum value can only be infinitely close;

Please refer to Figure 8, the vertex cache hit rate is not only related to the graphics processor hardware itself, but also closely related to the arrangement of the mesh data. If the triangle sequence of the model is T ₀ T ₁ T ₂ , then when drawing T ₁ and T ₂ triangles, all the vertices of these two triangles need to be read from the memory again, if the triangle sequence of the model is T ₀ T ₃ T ₄ , then when drawing T ₃ , the two vertices of the triangle are already in the vertex cache In , the GPU only needs to read one more vertex. When drawing T ₄ , it also only needs to access one vertex. Therefore, by modifying the triangle sequence of the model, the locality of the model can be increased to improve the cache reuse rate. The converted mesh model does not consider the problem of vertex hit rate, and the average vertex mismatch rate can be further reduced by changing the arrangement order of triangles, and the vertex cache optimization of the 3D model can reduce the load of obtaining model data, and can also reduce The amount of calculation required for rendering operations speeds up the drawing process;

In this regard, we have done a lot of work to optimize the rendering of the mesh. Hoppe uses a greedy algorithm to reorder the triangle sequence of the triangle mesh, resulting in triangle strips with a high vertex cache hit rate. The method of Hoppe’s method was improved, and cache-optimized triangle strips with arbitrary cache parameters were obtained. The ACMR values produced by these two methods are very close to the minimum value, but the number of triangle strips produced by this method is relatively small. Many, due to the deep layering of the data model and the large number of components, if this strip generation method is used, the number of triangle strips in the entire assembly model will reach an extremely large order of magnitude, which will lead to excessive drawing function calls, resulting in The graphics system is overloaded, which affects the rendering speed. Bogomjakov et al. proposed a general rendering sequence algorithm, so that the obtained triangle rendering sequence can obtain a good vertex hit rate in any capacity vertex buffer, but the speed is slow. Lin et al. The greedy method conducts a global search on the grid, and its heuristic conditions are many, and the ACMR optimization effect of the grid model is obtained, but its time complexity is high;

Sander et al. proposed a cache optimization method based on triangular rings. This method only performs a heuristic search near the last result. It has a good vertex cache hit rate while ensuring linear time complexity, but it belongs to known cache parameters ( cache-aware) algorithm, when the actual cache is smaller than the ideal cache, the vertex cache hit rate will seriously drop;

In practice, it is difficult to obtain the vertex cache parameters of the graphics processor. At the same time, in order to ensure the generality of the optimized model, the cache optimization effect should be unaffected by the actual vertex cache parameters as much as possible. Therefore, based on the literature, a new heuristic Search rules, under the premise of maintaining linear time complexity, not only ensure a good vertex hit rate in drawing, but also have adaptability to different capacity caches;

The algorithm uses a first-in-first-out (FIFO) vertex cache simulator with a capacity of s to simulate the situation of vertices entering and leaving the cache. In order to speed up the algorithm and maintain a high vertex cache hit rate, the algorithm Borrowing the idea based on triangle ring operation, by continuously searching for a local optimal vertex as a Fanning vertex, and then outputting the adjacent unoutput triangles containing this vertex, and finally obtaining a triangle sequence with a high vertex cache hit rate, the search is only in the candidate vertex If it cannot be found, it will be searched in other vertices in the vertex buffer. If all the vertices in the vertex buffer have been output, then a non-output vertex will be randomly selected as the Fanning vertex for output. The search process continues until the network until all the triangles in the grid have been exported;

It is known that when the ideal cache capacity of the cache parameter algorithm is smaller than the real vertex cache, the reason for the sharp increase of the ACMR value is that when the real cache is smaller than the set simulation cache size, the originally assumed hit vertices will have been replaced in the real cache Therefore, the GPU must revisit the data in the memory, and the later vertices in the triangle sequence will aggravate this phenomenon, causing the triangle sequence to be completely out of order and affecting the final rendering efficiency;

In order to overcome this problem, a new heuristic search rule is adopted, that is, the selected Fanning vertex must meet the following two conditions:

(1) After outputting the triangle ring of this vertex, the vertex must still remain in the vertex cache;

(2) The Fanning vertex must have the highest priority value of the triangle ring, and the priority value C(v) of the vertex is jointly evaluated by the position of the vertex in the cache and the degree of the vertex, and the priority value C(R) of the triangle ring is The sum of the vertex priority values of all unexported triangles in the ring

The vertex priority value C(v) can be calculated by the following formula:

C(v)＝ _Cp (v)+ _Ca (v)

in,

In the above formula, p represents the position of vertex v in the cache, s represents the size of the cache space, a represents the number of unoutput triangles adjacent to vertex v, and k ₁ , k ₂ , k ₃ are coefficients;

In the calculation of the vertex priority value, the vertex priority value that enters the vertex cache later is higher, so that even if there is a large gap between the simulated cache and the real cache space, the vertex can still hit the vertex cache. However, if only the vertex position is considered, A long and narrow triangle strip will be generated, making it difficult for the vertices in the vertex cache to be reused by subsequent triangles. Therefore, the evaluation of the degree of the vertex is also added during the search and selection process, and the adjacent unoutput triangles containing the vertex If the number is small, it will be given priority as Fanning vertices, which can increase the locality of the triangle sequence, so that the subsequent output triangles can fully reuse the vertices of the previously output triangles, reducing the possibility of long and narrow triangle strips;

Please refer to Figure 9. The input data of the vertex cache optimization operation is the mesh model converted from the solid model. After the optimization process, the cache-optimized triangular mesh model is obtained. After encoding and compression, the final Data model:

Step1: Establish the adjacency relationship between mesh vertices and triangles, and initialize the vertex priority value;

Step2: Select any vertex as the Fanning vertex;

Step3: Output Fanning vertices adjacent to unexported triangles, use the vertices of these triangles as candidates for the next selection, update the content in the vertex cache, and update the priority values of these vertices;

Step4: Perform a heuristic search on the vertices in the candidate. First, determine whether the vertex is still in the vertex cache after the triangle ring is output. If multiple vertices meet the conditions, calculate the triangle ring priority values of these vertices, and select a higher priority value. The vertex of the vertex is used as the next Fanning vertex. If the vertices in the candidate do not meet the conditions, then the same search operation is performed on the remaining vertices in the vertex buffer. If the Fanning vertex is still not found, it means that the vertices in the vertex buffer contain these vertices. The triangles of have been output, therefore, a vertex is arbitrarily selected as the next Fanning vertex;

Step5: When the number of output triangles is less than the total number of triangles in the model, turn to Step3: Otherwise, the algorithm ends.

The establishment of the adjacency relationship in the algorithm does not need to record edge information. The time consumption of this step is proportional to the number of triangles in the grid. During the triangle output process, each vertex is at most one Fanning point, and each triangle is visited at most three times. , and the cache update operation is only related to the cache size s, so the operation process consumes constant time, and the time consumed by the triangle ring priority value calculation is related to the average degree of the model, which is a small constant for an ordinary model , so the time consumption of this step is a constant. In general, the time complexity of the algorithm is kept at O(t), which will be proved by the experimental results later;

The test platform used in the experiment is IntelCorei32.13GHzCPU, 2.0GBRAM, the coefficients k ₁ =0.3, k ₁ =0.9, k ₁ =0.3 are set in the experiment, and the comparison vertex cache optimization algorithm is triangle fan method (FanSort) and general drawing sequence construction Algorithm (Bog), the triangle fan method and the algorithm all set the vertex cache size to 32. The reason for choosing these two algorithms for comparison is that the triangle fan method is fast and the optimization effect is good, and the algorithm is difficult to adapt to different capacity cache problems. And the improved, general-purpose drawing sequence construction algorithm can obtain good vertex hit rate in any capacity vertex buffer;

Among them, model a is a gear model with 13884 triangle faces, model b is a sphere generated by modeling software, and the number of triangle faces is 20480. Both models c and d come from the 3D scanning database of Stanford University, and the triangle faces of model c The number of faces is 49954, the number of triangle faces of model d is 69451, the number of triangle faces of model e is a motor model, the number of triangle faces is 91948, the number of model f is a plate-shaped part in the rear axle of the car, the number of triangle faces is 180311;

From the data in Table 2, it can be seen that FanSort has the fastest processing speed, and the algorithm processing time is proportional to the number of triangles in the model, which is slightly longer than FanSort. Adaptability thus requires the computation of priority values for triangular rings, but is still many times faster than the BoG algorithm;

Table 2

Comparing the average vertex mismatch rate changes when running in different cache capacities in actual drawing, when the actual vertex cache capacity of the Fansort algorithm is smaller than the ideal vertex cache capacity, the ACMR value increases sharply, while the algorithm and the BoG algorithm have cache misses under different cache capacities The allocation rate is stable, and there is no drastic change, but the optimization effect of the algorithm is slightly worse than that of the BoG algorithm;

In summary, the algorithm has a faster processing speed and a better vertex cache hit rate under any cache capacity, which can improve rendering performance.

Example 3

In the schedule management model, under the guidance of engineering project management, operations research, and systematics, a 4D simulation management system and a schedule simulation model are established. With the management system as the application framework and schedule management as the drive, the project schedule, time, and manpower On the basis of the integration of materials and materials, more development points can be combined between project progress management and BIM visualization, and strengthen the process control of the project construction stage. Based on this, a 4D digital progress management model that establishes BIM three-dimensional integration time and resources is formed;

The basic content of project schedule management includes project schedule preparation and project schedule control. Project schedule preparation refers to formulating a reasonable and economical schedule within the specified time. Project schedule control refers to checking the actual Whether the progress is carried out according to the plan requirements, if there is a deviation, find out the reason in time, take necessary remedial measures or adjust and modify the original plan until the project is completed;

1) The process of project schedule management mainly includes steps such as activity definition, activity sequencing, activity resource estimation, activity time estimation, schedule preparation, and schedule control. Activity definition is generally established on the basis of project scope determination and work breakdown structure. For the specific activities included in the deliverables, the ordering of activities needs to refer to the project scope description, activity list and attributes, and milestone list, and is completed through methods such as precursor diagrams, arrow diagrams, and condition diagrams, and finally obtains the dependencies and constraints among activities. , activity resource estimation is to calculate the number of man-hours and shifts required for each activity on the basis of determining the engineering quantity, so as to obtain the activity resource demand;

Activity time estimation is based on activity resource estimation and logical relationship determination, estimates the duration required for each activity, and further determines the start time and end time of the activity. On the basis of completing the above work, the project schedule can be compiled , and use the target plan to control the project schedule. The work of each process of project schedule management is carried out after the project team determines the preliminary plan. In the practice of project schedule management, there is no boundary between various tasks, but overlaps and influences each other , here the schedule management process is clearly defined to facilitate theoretical analysis;

2) After the activity definition, activity sequencing, and time estimation are completed, project resources and other constraints should be considered comprehensively, so as to determine the start and end time of project activities, implementation plans and measures, and complete the preparation of the entire project schedule. , can reasonably arrange the time of the project to ensure the achievement of the project target, it is the basis for project progress control during the construction process, and can provide a basis for resource allocation and time allocation;

3) The project schedule plan has completed the schedule arrangement of each activity. However, there are many unpredictable problems during the construction process, and deviations often occur during the execution of the plan. The project management personnel are required to correct the deviation in time and adjust the plan so that the project follows the contract. The control of the project schedule refers to the activities of checking, comparing, analyzing and adjusting the implementation progress during the project implementation process after the project schedule is formulated to ensure that the overall goal of the project schedule is realized. Schedule control is a recurring routine activity that mainly includes: determining a fixed reporting period, controlling the entire execution process of the project, comparing the actual progress with the planned progress, such as project delays, exceeding budget or not meeting technical specifications, Actions must be taken to bring the project back on track, and if the plan has been revised in response to changes, a new baseline plan must be established;

The dynamic monitoring of project progress mainly includes follow-up inspection of progress execution, sorting, statistics and analysis of collected data, and comparison of actual progress and planned progress. The comparison between actual progress and planned progress can be made using Gantt charts, network diagrams, s Curves, progress tables and other forms intuitively reflect the gap between the two. Through comparison, it can be found that the actual progress is ahead of the planned progress, delayed or consistent. The process of project progress adjustment includes: analyzing the cause of the progress deviation and analyzing the impact of the deviation on the follow-up work Determine the constraints affecting the total construction period and follow-up work, take corresponding schedule adjustment measures, and implement the adjusted schedule;

With the continuous deepening of project management concepts, schedule planning technology has developed rapidly, supporting project schedule management, and bringing great benefits to projects. Currently, commonly used schedule planning technical tools include Gantt charts, critical path methods, and plan review techniques. The development of schedule planning technology has probably gone through three stages: Gantt chart, network planning technology, and critical chain method;

The Gantt chart is a horizontal bar chart, which is widely used in construction period planning and schedule arrangement. In the Gantt chart, project activities are arranged vertically on the left side to display the work content. The horizontal axis indicates the progress time, and the horizontal bar indicates the project activity time. Bar chart It can display the start time, end time and duration of each job. The Gantt chart is simple, clear and easy to read. It can clearly express the activity time difference and logical relationship of work tasks. It can be used at any level of WBS. The time unit can range from year to day or even hour. In addition to being used to make progress plans, the Gantt chart can also be used as a progress control tool to display the actual progress status in the form of a bar graph, and intuitively compare the actual progress with the plan The deviation between schedules is used as the basis for schedule adjustment. In addition, Gantt charts can be used for resource optimization, resource planning and cost planning. Gantt charts are currently the most commonly used construction schedule management methods for substation projects;

The construction progress management system should start from time planning, integrate network planning technology, and realize the comprehensive management of progress and resources. It should include project scope planning and responsibility allocation, comprehensive plan preparation and optimization, target management, plan feedback and analysis and update, Report and information release functions, etc.;

Project scope planning and responsibility allocation, project scope definition and control can make project participants agree on what the project should do and should not do. The scope definition can further decompose the deliverables into smaller and manageable parts. work package;

Compilation and optimization of comprehensive plans and project schedule preparation should be dominated by construction schedule plans, and relevant functional departments formulate their own business plans, thus forming a comprehensive financial fund plan, design plan, marketing plan, procurement plan, etc., including most of the content of project management The schedule plan, after the project department or the contractor completes the master plan of the construction and installation, can combine the project progress in the schedule plan management professional software to prepare the quality visa work plan for the construction operation, and the design review department can also formulate the corresponding drawing demand plan , the purchasing department can support the procurement plan. In addition, the quality inspection department or personnel can formulate a work plan for the submission of quality documents for review/inspection in combination with the procurement plan. Work out the quality inspection and evaluation and related work plan, and the safety department can prepare the on-site construction safety environment plan;

Target management, the establishment of project target plan facilitates the tracking and control of the project progress, can compare the progress performance with the target plan, analyze the progress situation, find deviations, and take timely measures to correct deviations, or update the target plan, progress Professional management software should have the function of establishing and maintaining goals, keep the current plan as the goal, have the function of combining the main goals (schedule, resources, costs) with the project plan, and have the function of comparing multiple target projects in one project. Visual project portfolio analysis and comparison function, target monitoring value setting, regular monitoring function, warning reminder function, easy to implement plan exception management, key target information can be summarized layer by layer, and targets can be linked at different levels such as EPS, project, and WBS ;

Plan feedback, analysis and update. Analysis is the basis of control decision-making and optimized management. Target and actual feedback are the basis for analysis. The content and depth of progress analysis have different requirements for different management levels. For engineering construction projects, the progress analysis required Contains: overview of responsibilities, recent progress arrangement, summary of project quantity completion, including: completion of current period, cumulative completion, completion of plan requirements, difference with target plan and progress trend, resource analysis, including: current period, cumulative Value, planned value, difference, labor productivity, resource usage, and cost. Due to the diversity of objectives, the time limit for job feedback confirmation is different. For different types of objectives, different analysis cycle control measures can be adopted;

Report and information release function, standard report reflecting the plan arrangement, standard report reflecting the actual progress, standard report reflecting the comparison between the plan arrangement and the actual progress, providing web publishing, and publishing the standard report or graph into a web page;

The creation of project schedule data is an important preparatory work for realizing BIM-based schedule management. Project management software such as Project integrates functions such as Gantt charts and network plans, and the grid information model based on GIM standards carries a large amount of available information of substations. Construction The creation of progress data can be based on the three-dimensional data platform, on the basis of applying WBS technology to decompose the project work structure, and using project progress management software such as Project as a tool;

First, the basic information of the project should be collected, and then the task details of the project should be determined. After the project file is established, the input tasks can be prepared. The stage of input tasks is usually called activity definition in the process of project management;

Activity definition is usually completed under the guidance of the scope statement and work breakdown structure WBS. According to the situation of the project, the WBS can be established first, and then the task list can be established, or the WBS and the task list can be established at the same time. How many methods can be used to input tasks into the Project software? Type, you can directly add the tasks that come to mind, regardless of the order and related task groups, and then adjust and organize them later, you can think about the project from beginning to end in order, enter the project in order, you can consider the project first The entire stage, and then add tasks and subtasks;

It is also possible to consider what work the project will implement in terms of milestones and deliverables, and enter these tasks as tasks, thus creating a task list;

After developing the task list, sorting the tasks, and establishing the task outline, and possibly customizing the work breakdown structure WBS code, the next step is to develop the task schedule. The project schedule is to complete the tasks, submit the deliverables, pass Milestones, the roadmap for finally completing the project goals on time, formulating an accurate and feasible schedule that truly reflects the operation of the project, it is necessary to enter the task duration in the software, determine the relationship and dependencies between tasks, and arrange the progress of individual tasks to meet the requirements when necessary. Specific time requirements, so that an outline of a real project schedule can be obtained. At this time, the duration of the task and the duration of the entire project can be known from the software;

The completion of project tasks requires resource allocation. With the clarification of tasks and the scheduling of the schedule, resources must be actually pointed out in the project plan, and the accuracy of the schedule can be improved by adding resources to the project. Know in advance in the allocated time Whether there are resources overloaded and assigned too much work, track the progress of the project according to the resource man-hours, track the use, cost and consumption of raw materials in the project, and confirm that all tasks are assigned responsible and reliable resources. Once the tasks and resources are identified, it is necessary to match the tasks and resources together and create an "assignment". After the personnel, equipment and material resources are assigned to the tasks, Project can create a project schedule, which not only reflects the project calendar, task duration, and dependencies and restrictive, and can also reflect the calendar and availability of assigned resources;

After the project scope is defined, the task schedule is arranged, and resources are allocated, the project planning phase is not over. Usually, we need to check the results to determine whether the project plan meets expectations and requirements. If the project cannot be completed on time according to the plan, It is necessary to adjust the project plan until it meets the expectations and requirements. After making the adjustment, the project plan still needs to be re-examined. Adding resources to the task may end the time earlier, but it may also cause an increase in cost. If more tasks are assigned to Existing resources may cause excessive allocation of these resources. In order to save time and cost, individual tasks, deliverables or stages may be abandoned. After balancing according to project requirements, the project plan can enter the implementation stage;

Please refer to Figure 10, the analysis model primitive is the material basis of the entire 3D information model, and all component objects and their attributes and operations are defined here. In other words, the core data of the model are concentrated in the model primitive, and the model primitive is The final carrier of 3D information model data, for this reason, the study of the data structure of the 3D information model also comes down to the study of the data structure of the model primitives;

In the power grid information model, the data structure of the model primitive includes two types: basic data and extended data;

Basic data includes geometric data, physical data, functional data, etc. This type of data describes the characteristics and properties of the model component itself. It is inherent in the component itself. As time and the environment change, the basic data will not change. Data includes technical data, economic data, management data, etc. Most of these data are information or materials associated with model elements generated during the project management process. It is subject to specific stages and environments of the project and does not describe the model diagram. The characteristics of the element itself have a certain degree of independence. The power grid information model can integrate extended data to make BIM technology and function expansion possible. A large number of indirect data associated with model elements are integrated into the information model to form A complete and unique power grid information model can greatly expand the functions and applications of BIM, maximize the value of BIM technology, integrate time data into the power grid information model, and realize the progress management based on BIM technology;

Through the analysis of the 3D model structure based on BIM technology, it can be concluded that the extended data of the model graphic element is the foundation of the realization of the function of the power grid information model. If the power grid information model integrates other extended functions, such as: schedule simulation, cost calculation, etc., it must be The corresponding extended data is integrated into the model primitives. The establishment of the 4D model still uses the architecture of the 3D model. The main difference between the two lies in the difference in the data structure of the model primitives. On the basis of the 3D grid information model, the construction plan data By integrating with the 3D geometric data and associated data of model primitives, a 4D power grid information model can be established to realize 4D simulation and other functions;

The application program designed with the MVC structure provides a functional area that can display multiple views for the same database. This structure is mostly used in the design of distributed application systems, and can better separate the data layer from the table layer. Developed based on MVC The application program is divided into three modules: the model layer, the view layer and the control layer. The separation of the three enables the same model to be displayed in multiple views. When the user changes the model data through the control layer of a certain view, other views that depend on this model will undergo associated changes , as long as the data changes, the control layer will notify all views of the change, so that the display can be updated immediately. Combined with the system functional requirements, the BIM-based 4D system can be designed in the MVC mode;

Please refer to Figure 11. The system model layer can realize the business logic in the system. After analyzing the GIM 3D information model through the 3D platform, the spatial data of the model components are exported to the DWF 3D model library, and the construction attribute data of the model components are exported to In the SQL database, through a platform similar to Project, the construction progress data is created and stored in the SQL database. Then, the association between the three-dimensional components and the two-dimensional WBS elements is established through the ID number of the model components, so as to realize the integration of spatial data and progress data. The system view layer displays the model information in different views or display forms, displays the construction progress based on DesignReview, conducts construction simulation, and uses the attribute table control to realize the display of specific information such as component construction start time, end time, engineering quantity, and materials. The control layer handles the interactive operation between the user and the system, coordinates the model and the view, and sets up an independent progress control module to facilitate comparative control of the construction start and end time of the components, based on the MVC system architecture;

Please refer to Figure 12. The 4D system based on BIM needs to be established on the basis of project planning technology and 3D power grid information model technology. It can be realized by comprehensive application of database technology and system development technology. After analyzing the 3D platform and Project software, it can Build an MVC-based system architecture implementation process;

At present, the application of related technologies in schedule management is isolated. Although the application of a certain technology alone has brought great benefits to project management, it is far lower than the benefits of integrated applications between technologies. The emergence of BIM and related technologies has brought great benefits to project management Project management brings great value and convenience, especially the creation, sharing and transmission of information throughout the project life cycle, which can ensure effective communication of information. Only by integrating relevant information technologies and building a BIM-based progress management system, In order to eliminate the disadvantages of traditional information creation, management and sharing, better realize the informationization of engineering project schedule management, thereby improving the efficiency of project management;

Please refer to Figure 12, the timeliness, accuracy and availability of progress information provided by the system are not high, and cannot meet the information needs of all parties involved in the project at various stages, and the efficiency is low. Analysis, combined with the characteristics of BIM technology, integrate its own advantages and derivative functions into schedule management, build a schedule management framework system based on BIM technology platform, try to make up for the shortcomings of traditional management methods, and build a BIM-based schedule management application framework system;

The BIM-based schedule management application framework system can visually show the improvement and perfection of schedule management methods and tools after the introduction of BIM technology. The value of schedule management theory and method, because the BIM technology model can carry the information required in the project life cycle management, so the BIM information platform and functions generated by BIM technology are conducive to the whole process of project schedule management, and its benefits penetrate into the schedule plan and all aspects of control;

On the basis of the existing progress management system, the project should use the BIM information platform as the core to establish the relationship between BIM and WBS network plan, so as to comprehensively utilize various methods and tools to improve the progress management process and increase project benefits;

Please refer to Figure 13. The core of the BIM-based schedule management system is the BIM information platform. The BIM information platform can be divided into three subsystems: information collection system, information organization system and information processing system. The three subsystems are in a progressive relationship , only when the pre-order system work is completed, the follow-up system work can continue. The engineering project information mainly comes from project participants such as the owner, designer, construction party, material and equipment suppliers, including information related to progress management in the entire life cycle of the project. All information, after the information collection system completes the collection of project information, the information processing system performs coding, classification, storage and modeling of information in accordance with industry standards, specific rules and related requirements. The information processing system can use the system structured The information supports the progress management of engineering projects, provides functions such as construction process simulation, construction plan analysis, dynamic resource management and site management, and the overall framework of the BIM information platform.

Example 4

In the comparison model, using analysis research, experimental verification and other research methods, by analyzing the real-time performance of information collection technology for construction site information collection and the integration of BIM for engineering information, aiming at the management needs and challenges faced by the construction side of power transmission and transformation projects To solve the problem, study the collection method of on-site construction progress data and the reconstruction method of real-time model, and propose a construction progress control method based on BIM;

After the critical chain is identified, it is necessary to calculate the size of the buffer, and the size of the buffer is set based on the safe time of the process. Therefore, the next step is to determine the method for determining the safe time of the process used by the model;

There are many ways to determine the safety time. The following two methods are widely used, each with its own advantages and disadvantages. The parameters in the two methods can be adjusted to achieve the purpose of adapting to the actual construction situation:

Method 1: Establish an uncertain index system during the project construction period, and divide the project into four periods, including project planning and decision-making stage, project preparation stage, project implementation stage, project completion acceptance, and project uncertainty in different stages The number of indicators is different, and the impact on the progress is different. The uncertainty indicators of different stages in the entire construction period of the project are comprehensively evaluated, and the uncertainty of each construction stage is obtained through the calculation of the index system. According to a certain Proportionally extract the safety time from the procedures of each construction stage;

Method 2: Assume that the time required to complete a process follows a Gaussian distribution or a lognormal distribution. The longer the time allocated to a process, the higher the probability of completion. If the completion of an activity is estimated with a 95% probability, the time will be special. The completion time of the activity is often used as the safety time of the project task;

Method 1 is more complicated than Method 2. It needs to build an uncertainty index system according to the characteristics of the project. If the actual project is adopted, it will inevitably increase more management costs and time costs. However, the uncertainty of the actual project is calculated according to the system, and the extracted The method of safety time is more scientific and reliable, while the second method is simpler, easier to operate, and basically conforms to the actual construction, but because each process is different and affects each other, this method also has certain limitations ,

Due to the simple and easy-to-use nature of method 2, it is decided to choose method 2 to take the safe time of the process. On this basis, choose the statistical distribution that conforms to the characteristics of the duration of the project process;

Statistical distribution of process duration can mainly adopt normal distribution and beta distribution, while uniform distribution and triangular distribution are rarely used. Although these distributions are not as common as normal and beta distributions, they still exist with certain possibility;

When the statistical distribution is used to simulate the construction period, the construction period generated by different distribution simulations will have a greater impact on the results. Therefore, each process should try to choose a statistical distribution that is in line with the actual situation. MATLAB will be used to simulate and analyze the project progress. The characteristics of the above four statistical distributions are as follows:

(1) Normal distribution. Normal distribution plays a very important role in both theory and reality. It is the basis for analyzing other distributions. When the three numbers coincide, the probabilities of the process duration being greater than or less than the average value are completely equal, and the probabilities of the process being delayed or advanced are completely equal;

(2) Beta distribution. In general, Beta distribution is an asymmetric unimodal distribution with clear endpoints. According to the different values of its parameters α and β, the distribution has four variations: left-biased distribution, right-biased distribution , its distribution range is in [0, 1], and the value of the distribution is relatively stable, which is suitable for simulating and estimating the duration of the process;

(3) Uniform distribution, also called rectangular distribution, it is a symmetrical probability distribution, and the distribution probability at the same length interval is equally possible. When the duration of the process is uniformly distributed, the completion time of the process is within a certain range. Possible, the probability of occurrence is low during the construction process;

(4) Triangular distribution. Triangular distribution is determined by three parameters, the lower limit of the distribution, the mode, and the upper limit of the distribution. There are both discrete and continuous distributions, which are often used in business decisions, especially in the field of computer simulation;

In actual on-site construction, the estimation of the duration of the process is often very generous. This is because there are multiple layers of organizational relationships among the various construction entities. Whenever the superior assigns tasks to the subordinates, they often take into account the various aspects of the task. Due to uncertainty, a certain safety time is added to the task. When the multi-layer safety time is superimposed, the actual safety time given is quite considerable. The duration still presents the characteristics of left-skewed distribution. People usually finish the work when the planned time is about to run out or report the results of the process after the planned time runs out. In short, most of the safe time in the process is wasted. Wasted. According to the idea of critical chain project management, the process time will always expand automatically until it takes up all the available time. The more time there is, the more time it takes to complete a task. This view explains the above phenomenon;

Therefore, without considering the influence of human psychology and bad behavior factors, and reducing the safety time of the process, the distribution of the process duration should obey the right-skewed distribution, assuming that the total time of a process is recorded as "1" In actual construction, the completion time of this process is roughly biased towards "0.7-0.9" days, which obeys the left-biased distribution of Beta, and without considering the influence of human factors, the completion time of process execution should be biased towards "0.5-0.7" days, obeys the right-skewed Beta distribution. According to the idea of critical chain project management, in order to eliminate the influence of human factors, the safety time of the process should be removed. Therefore, when simulating the duration of the process, the statistical distribution of the process duration should be right Skewed distribution, the safety time reserved layer by layer will be treated as a buffer, but the completion time of a process cannot be completed in "0" time, no matter how much safety time is, it is difficult to occupy half of a job, so it should be The right-skewed Beta distribution graph moves to the right of the coordinate axis as a whole, so that the average completion time of the process is roughly within "0.5-0.7" days, and it may take more than "1" day to complete the process;

Based on the above content, it is considered that the duration of the process should be simulated and estimated using the Beta right-skewed distribution with the initial value not zero. At the same time, the selection of the parameters of the Beta distribution should have certain requirements. Second, because each process has its own characteristics and has different degrees of uncertainty, the estimation of its duration can also be distinguished by selecting the parameters of the Beta distribution;

From the above, it can be seen that there are four types of graphic distributions in the Beta distribution, namely, a downward wave curve, an upward wave curve, a left skewed curve, and a right skewed curve;

In probability theory, Beta distribution, also known as β distribution, refers to a set of continuous probability distributions defined in intervals, with two parameters α, β>0, and its important properties are shown in the following formula,

(1) mean value:

(2) Variance:

It can be seen that the above two equations are combined into a system of binary quadratic equations with infinite sets of solutions. Knowing α and β, the mean and variance can be calculated respectively, but it is difficult to find the values of α and β when the mean and variance are known. , through the MATLAB design simulation, the value range of α and β is stipulated as 0:0.1:10000. Since the required distribution graph is a right-skewed graph, the value range of the mean value is stipulated as 0.3:0.05:0.5, and respectively calculated The variance value and the simulation results are stored in the A11 to A51 matrices respectively, the first column is the α value, the second column is the β value, and the third column is the variance value, and then the data in the A11 to A51 matrix can be used as needed , select the appropriate mean and variance, and select the corresponding parameter combination to simulate the duration of the process. At the same time, because the conditions for the appearance of the downward wave curve and the rising wave curve of the Beta distribution are not clear, the selected parameter combination should be passed MATLAB simulates, draws its distribution graph, and applies it when it is confirmed that it is a right-skewed distribution;

Through MATLAB design simulation, it can be seen that the downward wave curve and the upward wave curve will only appear when the variance is large: when the mean value is less than 0.5 and the variance is large, the downward wave curve will appear, and when the variance is small, the right curve will appear. Skewed waveform curve, when the mean value is greater than 0.5 and the variance is large, an ascending waveform curve will appear, and when the variance is small, a left-biased waveform curve will appear, and the greater the variance, the greater the fluctuation of the curve, so it may be a downward waveform curve The peak of the rising waveform curve appears within the range of the curve fluctuation, it is difficult to see its skewness, and its exact shape will not be explored. The right-skewed Beta distribution with small variance is mainly used. At the same time, if the variance is too large, it is not suitable Applied to the simulation of process duration, the stability is difficult to meet the actual requirements;

According to engineering practice, it is easy to know that the longer the duration of a process, the greater the degree of uncertainty of the process, and the easier it is to delay. Through the division of the process duration, three parameter combinations are given, corresponding to the process. The degree of uncertainty is to make the Beta distribution more suitable for the actual situation, see Table 3 for details;

degree of process uncertainty Process duration (α,β) average variance value Big t>80 days (3,3) 0.5 0.0357 middle 40 days ≥ t> 10 days (2,3) 0.4 0.04 Small t≤10 days. (1.5, 3.5) 0.3 0.035

table 3

Corresponding to the above three situations, when simulating the beta distribution of the processes in the project network matching different parameters, in order to avoid the process simulation time being too short and not in line with the actual on-site construction, the beta graphs of the above three parameters are shifted to the right by 0.3 Unit, at the same time set the beta random distribution number not less than 0.15, so ensure that the minimum duration of each process is at least 45% of the original duration, in this case, the completion time of the process is within 60%-80% of the original duration time, and there is a certain probability that it will exceed the original duration, which is more in line with the actual situation, and the uncertainty is relatively large;

To sum up, it is considered that the processes in the project all obey the right-skewed Beta distribution and are independent of each other. The safety time is taken as the difference between the duration of the process under the 95% completion probability and the duration under the 50% completion probability. The formula is as follows:

T _k ＝[F(x)I _x＝0.95 -F(x)I _x＝0.5 ]×t _k

In the formula, F(x) is the distribution function of Beta distribution, T _k is the safety time of process k, and t _k is the duration of process k;

BIM-based schedule planning and control comprehensively apply technologies such as BIM, WBS, and network planning. The schedule formulation is based on BIM model information, and the traditional schedule management software interface is used to establish the work breakdown structure, construction period estimation and work logic relationship arrangement. and other steps;

Before the preparation of the project schedule, the scope management and work definition of the project must be completed first. WBS is considered to be one of the most important tools for planning and controlling the content and scope of project work. Similarly, the first step of the BIM-based project schedule is to establish The work breakdown structure is generally completed with the assistance of related software or systems;

The establishment and coding of WBS is the key to link the information of BIM model component elements with the information of operation progress, resources, costs, etc., so as to realize the direct application of BIM model information in schedule management;

The project work breakdown structure is to decompose the project objectives, tasks, scope of work, and contract requirements into project units that are independent, mutually influential, and interrelated according to system principles and requirements, and use them as a project unit for planning, implementation, control, and information transmission. A series of project management work objects. Through project management, all project units are combined into a whole work to meet the comprehensive planning and control requirements. It is essentially a top-down, layer-by-layer decomposition expression of project tasks. so that each task is assigned to an appropriate place in the overall project structure;

WBS is the basis of time planning in project management. The work breakdown structure method uses systematic thinking to decompose the project, prevents the lack of items in the project network plan, and performs man-hour estimation, construction period estimation, resource allocation, and establishment of overlapping for each decomposed unit. Relationship and time optimization, in order to achieve the optimal management of the project time plan, time control in the process of project implementation is also based on the decomposed units;

WBS creates conditions for computer-aided project management. The application of computers to project management is a symbol of modern project management. In the process of project implementation control, classified resources and progress information are collected through the WBS coding system to ensure that information is passed through unified and consistent annotations The method is annotated, and by inputting the names and overlapping relationships of the work units at each level by the computer, bar diagrams, network diagrams, and 4D models can be automatically generated, and the progress status of the project can be checked at any time during the project implementation process, and the progress period is automatically generated by the computer Report;

From the perspective of the creation process, the work breakdown structure (WBS) is to decompose a functional entity (project) into sub-items according to the tree diagram, and then decompose it into several relatively independent work units step by step, and determine each work unit. Tasks and their subordinate work (or activities), in order to organize the project more effectively;

In the BIM-based schedule management system, WBS compilation is realized by computer. For the obvious and necessary work of the project, the information in the BIM model can be directly used to check the model or export the schedule to determine;

For work with a certain degree of concealment, based on experience, or referring to previous project practices, list the work necessary for a complete project, complete the input and coding of WBS elements through the computer software system, and construct project operations and BIM models Component linkage;

Based on the BIM schedule system, an unlimited number of WBS milestones can be added, and these milestones can also be used to calculate earned value. Milestones are assigned at the WBS level, and each milestone is assigned a weight to indicate its importance to the project schedule. When When a WBS milestone is marked as completed, the module will use its weight to calculate the percent complete for all activities included in the WBS level, apply the percent complete to all activities under that WBS level, and roll up to the WBS, for example, If a particular level of WBS contains 10 activities, and actual completion dates are entered for 5 of them, and 4 WBS milestones with equal weights are also assigned to that WBS level, but only one of them is marked as completed, the module Completed WBS milestones will be used to calculate the percent complete of the WBS level, which is 25%, even if the activities contained in the WBS level are 50% complete;

If a WBS element has a total of 4 weighted milestones, all of which have a weight value of 1.0, marking one of them as "Completed" means that the WBS element is 25% complete, if the milestone has a weight of 9.0 , while the other 3 all have a weight of 1.0, marking the milestone as Completed means that the WBS element is 75% complete, and the module calculates the percent complete based on the weighted milestone using the following formula: Actual Completed Milestone Weight / total weight of all milestones, applying the above formula to the above example, the weight of completed milestones is 9.0, divided by the total weight of all milestones of 12.0, the result is a percent complete of 75%;

WBS earned value BIM-based system can define earned value settings for specific WBS elements, so as to realize WBS earned value analysis. Earned value is a method to measure project performance according to project cost and schedule. This method compares the budget cost of work with To compare actual costs, earned value analysis is usually used for WBS elements, and earned value analysis can also be performed on jobs or groups of jobs;

Using the earned value function of the work breakdown structure, you can specify the earned value settings for calculating the selected WBS elements. The "earned value" cost refers to the total budgeted cost of the activities that have been actually completed since the project data date, and its calculation is as follows: earned Value = Budget at Completion × Execution Completion Percentage, the calculation method of Completion Percentage depends on the earned value method selected for the WBS of the activity;

The project schedule is a roadmap for completing tasks, submitting deliverables, passing milestones, and finally completing the project goals on time. The formulation of the project schedule is most related to time management. To formulate an accurate and feasible schedule that truly reflects the operation of the project, it is necessary to determine the operation Duration, logical relationship between tasks, and resource allocation, cost estimation, and budget setting;

After the work breakdown structure defines the project activities, it is necessary to estimate the operation time one by one. The operation time refers to the duration of the operation. Estimating the operation time is the core of the time plan. The ability of the team and the available professionals, equipment and funds are adjusted, and the estimation of the operation time needs to consider the internal and external factors that affect the construction period, which can be carried out by combining experience, historical data, research, Delphi method, modeling, etc.;

Based on the BIM schedule, when the work breakdown structure is completed, the association between the WBS code and the ID number of the model component is realized, and the basic data information of the corresponding model component can be viewed by selecting the job, so the estimation of the operation time can use the geometry of the model component , functions and other data, through the acquisition of engineering quantity information, combined with specific calculation methods, and through the reference of other project model experience and historical information in the system database, to complete the job duration estimation;

The BIM-based schedule system can be used to view and edit detailed schedule information of selected activities, including planned start and finish dates, actual start and finish dates, free float, total float, constraints, planned duration and actual duration, etc. You can view and edit the labor and non-labor unit cost values and material cost values of the job. In addition, the system provides PERT analysis to help estimate the duration. You can set optimistic duration, expected duration and pessimistic duration respectively. The system automatically weights the average to display the calculated duration. For the system The editing of the detailed progress information of the job in is also directly reflected in the change of the extended data of the model element;

When the duration of the activity is determined, the next step in creating the project schedule is to establish the logical relationship between the activities to indicate whether a certain activity must be started or completed after another activity. After the logical relationship is assigned, the project schedule is calculated Get the earliest and latest dates for each job;

There are usually four types of logical relationships from predecessor activities to successor activities:

Finish-Start (FS): The successor job can start only when the predecessor job is finished;

Finish-Finish (FF): The completion of the successor activity depends on the completion of the predecessor activity;

Start-Start (SS): the start of the successor depends on the start of the predecessor;

Start-Finish (SF): The successor job can only be completed when the predecessor job starts;

In cases where the successor activity cannot start or finish at the same time as the predecessor activity starts or finishes, a delay can be defined for the relationship, which is the time between the start or finish of one activity and the start or finish of the successor activity number, and the delay can be positive or negative, for example, a start-start relationship with a three-day delay means that the successor activity cannot start until three days after the predecessor activity starts;

Based on the BIM schedule, there are many ways to assign the logical relationship. You can use the activity network diagram to visually display the logical flow of the connected activities, or use the bar diagram to view the logical relationship according to time, or you can directly select the WBS activity to assign the relationship For other tasks of the project, after completing the setting of the logical relationship, the formulation of the network diagram and bar chart is completed. Multiple jobs can be selected through the system and the network plan or bar chart can be used for plan analysis, and the four-dimensional view of the selected job can be viewed. dynamic simulation;

With the clarification of project operations and the scheduling of the schedule, resources must be actually pointed out in the project plan. By adding resources to the project, the accuracy of the schedule can be improved, and the progress of the project can be tracked according to the working hours of the resources, and the raw materials in the project can be tracked. Usage, cost and consumption, confirm that all tasks are assigned with responsible and reliable resources, resources include labor and non-labor resources to perform all project activities, such as engineering currency and equipment, usually calculated by time and often assigned For other operations, material resources, such as supplies and other consumables, are calculated by unit price, not by hour;

The BIM-based schedule management system can add resources and create a resource hierarchy to reflect the organizational resource structure, and support the allocation of these resources to jobs, and can set resource classification codes without hierarchical restrictions for resource grouping and summary , and generate resource reports and overviews, and then analyze resource allocation and adjust project plans to avoid resource over-allocation and resource usage peaks and troughs. In addition, the system can compile resource plans to integrate resources, costs and schedules, so as to plan projects For effective control, after allocating resources through the system and specifying the expected budget amount used in the job, you can use the "Job Analysis Table", "Resource Analysis Table", "Job Histogram" and "Resource Histogram" during the project process. Graph” to track its usage;

After the schedule plan is initially completed, it is necessary to analyze the plan to confirm the rationality of the plan itself. The analysis of the high-level plan mainly includes: whether the content of the project plan is comprehensive, whether the operation is a detailed division of the minimum level of WBS, and whether it is convenient for planning Control: main resources, cost allocation, job duration, construction process logical relationship, construction process constraints, construction process time difference, main process handover points, whether work products and documents are assigned to corresponding WBS and job, etc., based on BIM progress The management system provides functions such as network optimization, schedule goal comparison analysis, earned value analysis, 4D simulation analysis, etc. Various analysis results play a significant role in reasonably determining project control objectives;

Please refer to Figure 14, the analysis of the schedule and duration should first review the consistency of the major milestones to ensure whether the overall target is consistent with the date stipulated in the contract, and then identify the key lines and analyze whether the duration of work on the key lines is acceptable. , under the comprehensive consideration of constraints, whether the start milestone date and completion milestone date meet the project requirements, through the graded plan formulated by multiple parties, analyze and check whether there is a large deviation between the summarized plan and the original plan, and the project participants should Communicate with each other and reach an agreement;

Please refer to Figure 15 and Figure 16. The BIM-based progress management system provides WBS work list view, cross-lane view, network view, and 4D view to analyze the rationality of the job duration and logical relationship. Through the cross-lane view or network view, you can It is convenient to find out the key lines and key tasks, and display them in different colors. If you need to adjust the key lines and key tasks, you can directly modify and edit them in the view. In addition, through the 4D view, you can directly simulate the work, which can be more accurate. Visually display the progress of the work, and find out whether the logical relationship between the work is reasonable or not;

If it is a time-constrained project, the completion time should absolutely take precedence over other factors, but it still needs to balance the budget constraints and meet the project scope. If the project completion time is to be advanced, first check the schedule itself to confirm all pre-set The accuracy and necessity of schedule control factors, review and update date constraints, duration, activity dependencies and activity calendars in the activity list or Gantt chart, in order to affect the end time, only need to adjust the key activities, which can shorten the key Path job sequence, make another job sequence become the current critical path, and ensure that the path ends before the target completion time;

The use of resources is the most important limitation in the project. After the resources are allocated to the work, it is necessary to check the workload and the allocation of work resources to ensure that all resources can be better utilized and allocated to appropriate tasks, and avoid under-allocation or over-allocation. , When resources are under-allocated, when resources are not directly performing project work, resulting in failure to complete on time, quality degradation, and increased costs, when resources are over-allocated, resources need to be continuously overworked, man-hours exceed available hours, and more will be paid for man-hours more fees;

Before the work starts, you can view the schedule and analyze the resource allocation, find under-allocation or over-allocation, and make necessary adjustments to maximize resource contribution and reduce the risk of resource allocation. The purpose of the review is to maximize the workload , can reduce the waste of resource costs, and can also make the most of key resources. The BIM-based schedule management system provides resource allocation analysis functions. By viewing the detailed information of selected resources in the resource worksheet, check the resources to determine whether the availability can be modified. To reflect the real demand of the project for resources, you can adjust the scope of the project, increase or decrease the WBS work items, balance the resource load, use the limit to delay the start of a resource, or adjust the duration, split or delay the work until the resource has time Execution, you can also adjust the budget, invest more money to increase resources, under the premise of the same skills and availability, you can add under-allocated resources to the work to reduce or replace over-allocated resources, resource allocation analysis;

By arranging cameras in all directions of the construction site, real-time progress information of the construction site can be collected, images used to generate real-time models can be integrated, and these pictures can be used for progress management. The following problems need to be dealt with. Reconstruction forms a real-time model, then compares the reconstructed model with the planned model, and finally calculates the progress statistics. The 3D reconstruction requires the following process:

1) Image registration is that the camera takes a large number of photos from various directions on the construction site, selects pictures taken from different angles at a time point, forms a group, and performs feature point matching on the pictures of this group. The so-called feature points are those that can reflect the scene The points of the initial structure, the detection of feature points can use SIFT feature detectors, feature detectors are often called corner detectors, but they do not only select corner points, but choose to have large gradients in all directions at a predetermined scale For any image position, use the SIFT feature detector because it has good invariance, can scale, view field and lighting transformation, and has a wide range of applications in the field of computer vision, SIFT is translated into scale invariant feature transformation, It can convert image data into scale-invariant coordinates relative to local features. The steps of SIFT image feature point formation are as follows:

1. Scale space extremum detection, searching all scales and image positions, and identifying potential points of interest for scale and rotation by using Gaussian differential functions;

2. Key point positioning. For each candidate position, a fine-fitting model is required to determine the position and scale. The key points should be selected according to the stability of the key points;

3. Determine the direction. According to the local gradient direction of the image, assign one or more directions to the position of each key point. All subsequent operations on image data are relative to the direction, scale and position of each feature. transformations, thereby providing invariance to these transformations;

4. Key point description, in the neighborhood around each key point, the local gradient of the image is measured at a selected scale, and these gradients are transformed into a representation that allows relatively large changes in local shape and lighting changes;

Through the acquisition of feature points by SIFT, a large number of features will be formed, and these features will densely cover the image in the entire scale and position range. Usually, the number of feature points obtained depends on the content of the image and the selection of various parameters, but There is a typical size, that is, an image of 500*500 pixels will generate about 2000 stable feature points, and to detect small objects in a cluttered background, at least 3 features need to be correctly matched from each object to perform Reliable identification.

2) After the feature points are detected, start image matching and recognition, the method is as follows: First, extract SIFT feature points from a set of reference images and store them in the database, by comparing each feature point in the new image with the previous The database is compared, and then the candidate matching features are found according to the Euclidean distance of the feature vectors, and then the new graphics are matched;

After the feature points are detected on the collected image data set, these feature points need to be matched. The matching method is the SIFT descriptor, which captures the intensity gradient on the pixel window centered on the detected key point, and then, these Pixels are classified into 4*4 sampling windows, where each sampling window and intensity gradient histogram are stored in 8 basic directions, then the descriptor becomes a feature vector of 4*4*8-128 dimensions, SIFT descriptor Match feature points by calculating the distance function of two matched intensity gradient histograms. Feature point matching uses the nearest neighbor matching method. If the number of features is large enough, the KD tree matching scheme can be used instead. In order to minimize Calculation amount, ANN priority search algorithm can also be used;

Mis-matching will occur when matching features. In order to eliminate errors, the ratio test method is adopted. The specific method is as follows: For the feature descriptor in image i, two nearest neighbors can be found in image j, and their distances are d1 and d2, if d1/d2<0.6, is the match we are looking for, if multiple features in image i match the same feature in image j, since one of them is a wrong match, then these wrong matches will be deleted item;

Due to the sensitivity of the reconstruction algorithm to false matches, the debugging method needs to be further improved, that is, once a matching feature is detected in an image pair, RAXSAC is used to robustly estimate the fundamental matrix of the image pair, and the fundamental matrix forces the corresponding features to be in the viewpoint Must be consistent under the transformation, namely: P, 'FP, -0 (P, and P, are point coordinates, and F is the fundamental matrix), in our model, in each iteration of RANSAC, calculated using the eight-point algorithm fundamental matrix, and then normalize the problem to improve robustness to noise;

The RNASAC outlier threshold is set to 0.6% of the maximum image size, that is, 0.006 times the maximum width or height of the image (for a two-dimensional image size of 2144*1424, approximately 12 and 9 pixels), by eighth of the basic matrix Running the LevenberMarquardt algorithm with three parameters can refine the fundamental matrix returned by RANSAC, and the purpose of removing false matches can be achieved by using the threshold suggested above;

If there are fewer matching items in the image pair, even after the basic matrix is iteratively fitted by RANSAC, there is still a high false matching rate. Therefore, a threshold of 20 matching items is set. If the matching item of the image pair is less than the threshold, Then the matching item has no reference value and is deleted. After finding consistent matches between all image pairs, organize these matches into tracks, and the tracks connect the matched key points across multiple images for the next stage. 3D reconstruction, at least two keypoints are tracked during the next stage of 3D reconstruction.

3) SFM is translated as motion structure, which aims to reconstruct the unknown 3D scene structure, and estimate the position and direction of the unknown camera based on a set of feature correspondences between images, bundle adjustment is to obtain powerful 3D reconstruction from a large number of sparse images A key tool that is robust in terms of image resolution, time, focus variability and illumination changes;

First, estimate the extrinsic parameters and intrinsic parameters of an image pair. Because the bundle adjustment is easy to fall into bad local minima, many researchers suggest that the initial image and camera parameters should be well chosen, and the SPM initial image pair should not only have a large number of matches item, but also have a large baseline so that the initial as-built scene can be reliably reconstructed. Image pairs that are difficult to describe with a homography satisfy this condition. A 2D image homography is a projective transformation that converts points Map from one plane to another, find homography between all image pairs using RANSAC with an outlier threshold of 0.4% of the maximum value of image width and height, and store feature matches that are outliers to the estimated homography percentage;

The initial image pair is selected such that it has the lowest percentage of pixels to the recovered homography image, such image pairs match at least 100, and the extrinsic parameters of this pair of cameras are estimated by using Niste's five-point algorithm, which is then visible to the image pair Triangulate the trajectory of , after a two-frame bundle adjustment of this initial pair, add another camera to the optimization, choose the camera that examines the largest number of estimated trajectories, and then use the direct linear transformation (DLT) technique to initialize the new camera Extrinsic parameters, for this RANSAC step, use an outlier threshold of 0.4% for the maximum value of the image width or height, and for the focal length of the new camera, as well as the estimation of the intrinsic camera matrix, can be done using the focal length of the Exchangeable Image File Format tag of the EXIF-JPEG image initialization;

Starting from this set of initial parameters, while keeping the model constant, run the bundle adjustment algorithm, allowing only the new camera and the keypoints it observes to change, and finally, adding the points observed by the new camera to the optimization algorithm, When at least one existing restored camera observes the key point, the key point is triangulated. After the triangulation, the position of the camera can be well estimated. By considering all available To triangulate the ray pair of the keypoint and find the ray pair with the largest separation angle to estimate the condition. If this maximum separation angle is greater than a threshold, then triangulate the point. Once a new keypoint is added, Just run another global bundle adjustment to reconstruct the new scene, and finally, the error of the solution is minimized by the sparse bundle adjustment library. This process is performed for all cameras until no camera can observe more reliable reconstructed 3D points. , in this way, the reconstruction of the construction site model is realized;

4) The progress model generated by the progress management system has three representation methods, one is in the traditional BIM platform, the as-built model is displayed on the plan model with color difference or the as-built model is displayed as a plan model, and the other is the The virtual model is superimposed on the construction site, and the progress is also distinguished by color. The manager can see the construction progress very intuitively. The third method is to show the progress of the project with the real appearance of the completed building. The specific implementation process is introduced below;

Align the reconstructed model with the planning model to determine the absolute geographic coordinates of each camera. The absolute coordinates are estimated by translation, rotation, and uniform scale transformation of the image. The estimated method uses a closed-form solution of the absolute orientation of the unit quaternion, In turn, the reconstructed model can be registered into the planned model, and the planned model can be registered as a built scene, by registering the real-time reconstructed sparse 3D point set into the control point set of the planned 3D model to minimize the reconstruction point set After alignment with the sum of squared residuals between the models, the model reconstructed by the camera will be superimposed on the site under construction, so that, from the perspective of the model reflecting the progress:

The first way is that the manager can see the virtual 3D image of the planned model superimposed on the corresponding position of the construction project on the construction site on the day of inspection. Green, if a schedule is under construction on the day of inspection but not completed, then this part will display light green, if any work has not started on the schedule on the day of inspection, then this part will be will be displayed in red;

The second way is to display the real appearance of the building. The BIM schedule management system can display the plan model in the appearance of the real world. The formation of such an effect requires data: a set of key points, each of which contains a The 3D position is composed of a color averaged from all the live images where the key point is located, and the second is a set of cameras with known extrinsic parameters (translation and rotation) and intrinsic parameters (focal length and distortion in the height and width directions), The third is the mapping between each key point and all cameras that observe key points. The list of cameras that obtain key points, the position of the point in the local coordinates of the image, and the SIFT key point index can be stored by mapping. These data are stored in the system. Simultaneously, the camera is rendered into a view frustum. By accessing the camera in the reconstructed scene, the camera view frustum is texture-mapped into a resolution image. After registering the planning model with the reconstructed scene, the planning model takes the reconstructed Overlay the sparse scene, and display the overlaid reconstructed sparse image as the image of the plan model, so that what is presented to the manager is the real appearance of the completed building;

The third method is the three-dimensional display method of traditional BIM progress management, that is, on the BIM platform, the progress is reflected by displaying the color difference on the planning model.

No matter how detailed the plan is, it is impossible to foresee all the possibilities, and there will still be deviations in the implementation of the project plan. Tracking project progress and controlling project changes are the main tasks in the implementation stage. After the BIM-based schedule is completed, enter the project The implementation phase, the implementation phase mainly includes tracking, analysis and control, tracking the progress of the job, actually knowing when the assigned resources will complete the task, checking the deviation between the original plan and the actual progress of the project, and predicting potential problems: take necessary Corrective actions to ensure the steady development of the project under the constraints of completion deadline and budget;

In the schedule planning stage, under the BIM-based schedule management system, various technologies such as WBS, bar diagram, network plan, and BIM are comprehensively applied to complete the schedule, allocate resources and budget expenses. In the implementation stage, BIM-based schedule management can be used The progress curve, Gantt chart, 4D simulation and other functions provided by the system can track and control the progress of the project;

The project plan after analysis and adjustment achieves a balance between scope, schedule and cost, and can be used as a target plan. Project activities define progress information such as the earliest start time and the latest start time, so the system can provide multiple target plans , to facilitate progress analysis, the project target plan cannot remain unchanged, and needs to change as the project progresses. After tracking the project progress for a certain period of time, the deviation between the target progress and the actual progress will gradually increase. At this time, the original target plan will lose value. The target plan needs to be recalculated and adjusted. After entering the corresponding progress information in the system, the project plan will be automatically calculated and adjusted to form a new target plan;

The BIM-based progress management system provides the creation and update of target plans, and can also assign target plans to each job. When updating target plans, you can choose to update all jobs, or use filters to update jobs that meet the filter conditions. Specify the data type to be updated. After updating the target plan, the system will automatically calculate the project progress and balance the resource allocation to ensure that the resource demand does not exceed the resource availability. During the balancing process, the system will calculate the resource demand of all calculated tasks As the maximum amount available during the balancing process, during the job duration, if there are too few resources available, the job will be delayed. After selecting the resources to be balanced and adding the balancing priority, you can specify that the balancing will be prioritized in case of conflicts In addition, after the resource information is changed, the cost needs to be recalculated according to the engineering quantity provided by the BIM model, so as to obtain the correct value of the operation cost;

After the project plan is created, it is necessary to continue to track the progress of the project. The BIM-based progress management system provides various tracking views such as project tables, Gantt charts, network diagrams, progress curves, 4D models, resource curves, and histograms. Displays project data in form, Project Gauge displays project data in horizontal "bar graph" format, Project Gauge/Histogram displays project information in column and "bar graph" format, displays time-spread project data in either a spreadsheet or histogram format , the 4D view dynamically displays the building construction process in the form of a 3D model, the resource analysis view displays resource/project usage information in column and "bar graph" formats, and displays time allocation resource allocation data in the format of a profile table or histogram;

All tracking views can be used to review items, starting with a comprehensive review, and then performing a more detailed review based on work breakdown structure, phases, specific WBS data elements, and filtering and grouping functions to customize what is included in the tracking the format and hierarchy of information in the view;

During the project implementation phase, it is necessary to regularly input progress information into the system, such as the actual start time of the job, the completion percentage of the visual progress, the actual completion time, the calculation of the actual duration, the actual amount of resources consumed, and other progress information. Sometimes it is necessary to adjust the work breakdown structure, delete or add jobs, Adjust the logical relationship between tasks. During the progress of the project, it is very important to update the progress. The actual duration may be different from the original estimated duration. The sequence of tasks may change as soon as the work starts. In addition, new tasks may need to be added and unnecessary tasks deleted. Regularly updating the progress and comparing it with the target plan progress can ensure the efficient use of resources, monitor the project cost against the budget, and obtain the actual duration and cost in time to implement the contingency plan when necessary;

In the implementation stage, while maintaining the target plan and updating the progress information, it is necessary to continuously track the progress of the project, compare the plan with the actual progress, analyze the progress information, find deviations and problems, and take corresponding control measures to solve the problems that have occurred and prevent them. Potential problems, the BIM-based schedule management system provides a variety of analysis methods from different levels to achieve a comprehensive analysis of project progress. During the implementation stage, it is necessary to review the progress, resource allocation, and costs to make the project development consistent with the plan.

①Schedule analysis Progress analysis mainly includes impact analysis of milestone control points, critical path analysis, and comparative analysis of planned and actual progress. By viewing the milestone plan and critical path, combined with the actual completion time of the job, you can check and predict whether the project progress is in accordance with The planned time is completed, and the critical path analysis can be carried out by using the horizontal view or network view in the system;

Please refer to Figure 17. The comparison between the planned progress and the time progress is generally completed by comprehensively using the bar diagram comparison, progress curve comparison, and model comparison. The system can display three views at the same time to realize the comparison between the planned progress and the actual progress;

Please refer to Figure 18, you can set the color of the view to achieve the comparison between the planned progress and the actual progress. In addition, through the comparison between the project plan progress model, the actual progress model, and the site conditions, you can clearly see the growth process of the building. Identify progress and other issues during construction;

②Analysis of resource situation During the progress of the project, the analysis of the resource situation is mainly based on reviewing the difference in working hours to check whether the resources are over-allocated or under-allocated. The BIM-based progress management system can provide resource analysis tables, Resource histogram or resource curve for resource allocation analysis, the resource view can be combined with the Gantt chart tracking view to display the allocation status and usage status of resources in the selected time period, and timely discover resource allocation problems and resource allocation;

③Analysis of cost situation For most projects, especially budget-constrained projects, the analysis of budget cost situation in the implementation stage is essential. If the actual progress information indicates that the project may exceed the budget, the project plan needs to be adjusted. The progress management system based on BIM , you can use expense analysis tables, histograms, and expense control reports to monitor expenses.

After inputting the actual information of the job in the system, the system automatically uses the planned value, actual cost, and calculates the earned value to evaluate the current cost and schedule performance, track these values for a long time, and view the past expenditure and progress trends of the project, as well as future cost forecasts. earned value analysis;

After entering the actual progress information in the system, through the comparative analysis between the actual progress and the project plan, many deviations can be found, and potential problems in the project can be pointed out. In order to avoid problems caused by deviations, constant adjustments are required during the project process Goals, and take appropriate measures to solve the problems that arise. Projects often have a phenomenon that the completion time, total cost or resource allocation deviates from the original planned track. Corresponding measures need to be taken to make the project development and plan tend to be consistent. If there are major changes in the project Or seriously deviate from the project progress, it is necessary to re-arrange the project schedule and determine the target plan, adjust resource allocation and budget expenses, so as to achieve progress balance;

The correction of the project schedule can be realized by changing the duration of the implementation work, such as rushing to work, but usually it is necessary to increase the resource input such as man-hour consumption, and it is necessary to use the construction period-resource or construction period-cost optimization to select the shortened construction period, less resource input, and less cost increase. Another way is to change the logical relationship between the project implementation work or the realization of the overlapping relationship, without changing the duration of the work, only changing the start time and end time of the work, if these two ways are difficult to achieve the purpose of shortening the construction period, When the delay in the construction period is too serious, it is necessary to readjust the project progress and update the target plan;

During the progress of the project, the main corrective measures for resource allocation are: adjust resource availability, adjust allocation, such as adding resources, replacing resources, delaying work or allocation, etc., splitting work to balance workload, adjusting project scope, and the main measures for cost correction are : Re-examine the budget cost settings, such as the cost per use of resources, the fixed cost of the job, etc., shorten the job duration or adjust job dependencies to reduce costs, appropriately add, delete or replace resources to reduce costs, and reduce project scope to reduce costs;

For the adjustment of the schedule deviation and the update of the target plan, factors such as resources and costs need to be considered, and appropriate organizational, management, technical, economic and other measures should be taken, so as to achieve multi-party balance and achieve the ultimate goal of schedule management.

Example 5

Please refer to Figure 19, the application of the BIM-based project progress management system described in this embodiment, the platform function design is as follows:

(1) Realize the project management of substation construction simulation simulation, support the creation, deletion, import and export of projects;

(2) Support the data import of substation design results in GIM format and architectural results in IFC format;

(3) Support the import of conventional 3D model formats, including: STL, Dgn, Dwg and other formats;

(4) Support operations such as data query, modification and deletion, and realize the management and adjustment of terrain data. Basic geographic information data includes image data, digital elevation model data, and basic vector data;

(5) Image data includes satellite images, aerial images, scanned topographic maps, etc.;

(6) Digital elevation model data includes contour lines, discrete points, and grid data, wherein the grid data is obtained by converting contour lines or discrete points;

(7) Basic vector data include administrative divisions, place names, residential areas, transportation, water systems, vegetation distribution, agricultural and forestry land, etc.;

Support the import of individual and overall models of GIM models, IFC models, conventional 3D models (stl, dgn, dwg, rvt, 3ds, dae), and based on the D3Station platform, realize fast model analysis and visual display, and support model attributes Check;

Support the import of Dem high-level data, Dom image data, oblique photography and other terrain data, based on the D3Station platform, realize the analysis and visualization of geographic information data, and support the display of basic geographic information data including image data, digital elevation model data, and basic vector data , image data includes satellite images, aerial images, scanned topographic maps, etc. Digital elevation model data includes contour lines, discrete points, and raster data, where the raster data is converted from contour lines or discrete points, and the basic vector The data includes administrative divisions, place names, residential areas, traffic, water systems, vegetation distribution, agricultural and forestry land, etc. Thematic data of power grids include windy areas, ice-covered areas, polluted areas, earthquake zoning, dancing areas, mine damage areas, bird damage areas, etc. Transmission line channel data includes important industrial planning areas, environmental protection and water conservation, mining factory areas and cross-over data within the line channel range, and survey data includes professional data such as surveying, hydrology, meteorology, geology, and geophysical prospecting;

Model structure, analyze the GIM, IFC model structure, support the model structure function panel, view the hierarchical structure of the model, and highlight the model according to the model structure, not only the imported model will be included in the model tree structure, but also the model arranged by the site will be included in the tree structure,

Model management includes:

Character model: built-in rich types of character models, character types include: designer, supervisor, chief engineer, etc., attributes include: character height, character animation action, character material;

Vehicle model: built-in rich types of vehicle models, vehicle types include: ordinary cars, maintenance vehicles, etc., attributes include: vehicle length, vehicle width, vehicle height, vehicle material;

Vegetation model: built-in rich types of vegetation models, vegetation types include: ordinary trees, arbor trees, shrub trees, etc., attributes include: tree height, tree material;

Earthwork component model: built-in section information such as foundation pit and earthwork, the attributes include: the section size of the corresponding component, the material of the corresponding component, and the component is placed by linear drawing;

Architectural component model: Built-in cross-sectional information properties such as ground, wall, road, and isolation fence include: the cross-sectional size of the corresponding component, the material of the corresponding component, and the component is placed by linear drawing. Built-in models such as doors and windows, the properties include: The size information and material information of the corresponding model;

Safety protection model: There are rich types of safety protection models built in. The types of safety protection models include: safety warning lights, safety warning signs, etc., and the attributes include: the material of the safety protection model;

Green civilization model: built-in rich types of green civilization models, the types of green civilization models include: LED screen, nine cards and one picture, etc., attributes include: the material of the green civilization model;

Electrical equipment model: built-in rich types of electrical equipment models, types of electrical equipment models include: lighthouses, switch boxes, electrical boxes, lamps, cameras, etc., attributes include: material of electrical equipment models;

Mechanical equipment model: built-in rich types of construction machinery and equipment models, including: cranes, tower cranes, electric welders, bulldozers, road rollers, etc., attributes include: height, length, width, and material of mechanical equipment;

FBX editor: Realize the editing of model actions, through the addition of key frames, animate the imported model in the form of displacement and rotation, and can perform animation editing on all imported models to realize the animation of the model, and in the construction Embodied during the simulation process, it can edit animations of corresponding actions for different types of models. The FBX editor is an important part of the construction simulation simulation at present;

Site layout: Provide substation site layout area, various models can be placed in the 3D viewport, support calling and placing in the model management module, including: character model, vehicle model, vegetation model, land component model, building component model, safety protection model , green civilization model, electrical equipment model, and mechanical equipment model, select the corresponding model, fill in the relevant parameters of the model, and quickly realize the placement of the site layout model in the substation. After the model is placed, the model structure will also quickly realize the refresh linkage.

The construction management personnel import the project plan list, and fill in the actual progress time along with the project construction, realize the unified management of the project plan and the actual situation, truly reflect the actual differences, facilitate the control of the construction progress of different people, build the tree structure of the substation construction project, and support the substation project. Create, delete, import, export, fill in planned schedule information, fill in actual schedule information of the overall construction project, new support project creation and sub-subset creation, delete support project deletion and sub-subset deletion, import support conventional EXCEL, ACCESS , The import and export of MPP format files supports the export of EXCEL, ACCESS, and MPP format files. The plan progress information can be filled manually or automatically through the imported file, and the actual progress information can be filled manually or automatically through the imported file;

Obtain the tree structure data in the model structure, and by analyzing the corresponding relationship between the construction plan and the 3D model, establish an association relationship between the construction milestone plan, the first-level network plan, and the two-dimensional network plan task, and assign the time attribute to the model, and the 4D display of the component. Bind the model with each item in the project list, which cannot be repeated, supports multiple bindings, realizes the binding relationship between the tree structure model and the project plan list, and provides data support for the 4D simulation of construction progress;

Through the construction project tree structure list, the time axis information of each project can be displayed in linkage, and the weekly, monthly, and quarterly project progress can be quickly checked, the time axis of the planned progress and the actual progress can be intuitively viewed, and the planned progress time and the actual progress time can be compared The parts with differences are marked in red in the time axis;

Generate the overall growth animation of the substation through the list of planned progress and actual progress information, the binding relationship of the model, and the project timeline, and can control the playback, pause, acceleration, and deceleration of the animation. According to the start time and end time of the overall construction plan of the project, Through the growth of the model, it can dynamically display the overall construction progress of the project at different stages, and at the same time support the visual display of the progress of a single construction plan, realize the dynamic progress display of different dimensions and granularity, and support the animation display of the simulation of the planned progress and the actual progress at the same time;

You can customize the installation sequence of the components of the equipment, obtain the current equipment model, disassemble the equipment model through the FBX editor, add key frames with FBX, and combine the displacement and rotation of each component to complete the installation process of the equipment from beginning to end Simulate and simulate in sequence, and generate equipment installation simulation simulation animation;

Realize the path setting of the model, you can set the model displacement position, time, speed, substation construction simulation simulation by calling different construction vehicle models (transportation vehicles, hoisting vehicles, etc.), setting vehicle trajectory, channel distance, output safety distance and other parameters, Simulate the entry of construction vehicles in different scenarios and processes, verify the safe distance of vehicle transportation, and optimize the timing of construction vehicles;

Through the FBX editor, combine construction machinery, construction equipment and hoisting equipment, split the overall model by adding key frames, and restore the simulation process of equipment hoisting through the combination of displacement and rotation of each component;

Hard collision verification, in the process of equipment installation simulation, mechanical path simulation, equipment hoisting simulation, and installation process simulation, in the substation model form in this simulation state, to detect whether there will be a collision between entities, if there is a collision, the verification will fail Qualified, highlight the part where the model collides;

Soft collision verification is realized in the process of equipment installation simulation, mechanical path simulation, equipment hoisting simulation, and installation process simulation. In the simulation state, in the substation model form, through the setting of the electrical clearance parameter distance, the detection is the distance between two objects. Whether the distance meets the electrical clearance requirements, if the distance check fails, a prompt will be given, and the safety value and actual value between equipment or buildings will be marked;

By directly importing the project construction schedule Project file, the project schedule is automatically generated, including the plan name, plan content, person in charge, plan start time, plan completion time, etc. On this basis, the content of each construction schedule plan can be refined. Meet the actual work needs of construction managers and avoid increasing the workload due to repeated preparation of schedules in the system;

The progress management module can edit the personnel input plan of each sub-project, and through the access to the personnel entry and exit data in the personnel gate of the smart construction site, compare the actual number of personnel entering the site with the number of planned personnel entering the site, and prompt the situation of insufficient manpower arrangement , to analyze the possible impact on the construction progress of sub-projects, assist the management personnel to adjust the investment of construction personnel, and ensure the completion of the project on schedule;

According to the GIM hierarchical structure and the project schedule plan tasks, it realizes the 3D model simulation of the project progress, and displays the progress of the project construction in real time. At the same time, the delayed, normal, and unconstructed items are marked on the 3D model by color to show the progress of the on-site personnel. Management provides auxiliary decision-making support, and comprehensively uses drones and oblique photography technologies to establish a real scene model that restores the construction site, which can be used as a process record file for project progress management, as a basis for construction management summary and progress analysis, and provides a basis for progress management. On-site data support means;

Disassemble and reorganize the 3D design model through BIM construction simulation technology, conduct construction simulation for construction projects with complex construction technology and strict construction sequence requirements, and generate construction simulation animations, which are provided to the construction team and technical personnel for technical disclosure, avoiding the need The on-site text plan is unclear, which leads to the problem of unclear process flow.

It should be noted that in this article, if there are relational terms such as first and second, etc., they are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that these entities or operations Any such actual relationship or order exists between. Furthermore, the term "comprises", "comprises" or any other variation thereof is intended to cover a non-exclusive inclusion such that a process, method, article, or apparatus comprising a set of elements includes not only those elements, but also includes elements not expressly listed. other elements of or also include elements inherent in such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article or apparatus comprising said element.

The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it can still be described in the foregoing embodiments Modifications are made to the recorded technical solutions, or equivalent replacements are made to some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (10)

1. The project progress management system based on BIM, is characterized in that: described system comprises data model, progress management model and comparison model; The data model is generated by combining the three-dimensional data model expression method and the method of occlusion query from multiple viewpoints to identify hidden parts in the assembly. The progress management model is based on the analysis of the data model structure to establish a real-time model and generate a corresponding calculation model. The comparison model will be The real-time model and the planned model are superimposed and compared to provide a solution for the correction and adjustment of the construction progress. 2. The project progress management system based on BIM according to claim 1, wherein the data model includes a three-dimensional information model of the power grid, and the three-dimensional information model of the power grid is converted into a surface model by scanning entities, and the specific steps are: Let the points before scanning be A(XA, YA, ZA), B(XB, YB, ZB)...K(Xk, Yk, Zk), scan vector V(XV, YV, ZV), for these points along An, Bn...Kn are obtained after the scanning vector V scans the surface, and the line-surface network formed by these points is the boundary model of 3DGIS: An=A+V, Bn=B+V...Kn=K+V For curve scanning, select the curve Curve=(M1(X1, Y1, Z1), M2(X2, Y2, Z2)...Mn(Xn, Yn, Zn)) and change the tangent vector of the curve to Hn=Xn-Xn- 1, Yn-Yn-1, Zn-Zn-1, if there is a point A' scanned by A (XA, YA, ZA, 0), it is calculated by the following formula, where N is the surface normal:

By analogy, the conversion from the solid model to the boundary model is realized. 3. The project progress management system based on BIM according to claim 2, characterized in that: the three-dimensional data model includes a solid model and a grid model, wherein the solid model is used to describe the geometric and topological information of the parts, and the grid The model uses polygonal patches to form the geometry of the object. 4. The BIM-based project progress management system according to claim 3, characterized in that: the method of performing occlusion query to identify hidden parts in the assembly from the plurality of viewpoints comprises the following steps: (1) Generate a query object ID for the object to be queried; (2) start occlusion query; (3) Render objects that require occlusion query; (4) End the occlusion query; (5) Extract the number of samples that are queried by occlusion; (6) Delete the query object ID and recycle resources. 5. The BIM-based project schedule management system according to claim 4, characterized in that: in the identification algorithm of hidden parts, the calculated visibility value of parts at a certain viewpoint is:

Where: λ ₁ +λ ₂ +λ ₃ =1; Among them, λ ₁ , λ ₂ and λ ₃ are weights, and the initial setting of part visibility rate, part area contribution rate and part volume contribution rate occupies the same weight, that is, λ ₁ , λ ₂ and λ ₃ are all 1/3; After part i completes the occlusion query at all set viewpoints, the maximum visibility value of part i is obtained, namely

Define the critical parameter F _T (0<F _T <1). When the F value of a component in the assembly is greater than the critical parameter, the component is visible from the outside of the assembly, otherwise the component is hidden. 6. The BIM-based project progress management system according to claim 5, wherein: the recognition algorithm of hidden parts jointly evaluates the priority value C(v) of the vertex by the position of the vertex in the cache and the degree of the vertex, and The priority value C(R) of the triangle ring is the sum of the vertex priority values of all unexported triangles in the ring

The vertex priority value C(v) can be calculated by the following formula: C(v)＝ _Cp (v)+ _Ca (v) in,

In the above formula, p represents the position of vertex v in the cache, s represents the size of the cache space, a represents the number of unoutput triangles adjacent to vertex v, k ₁ , k ₂ , and k ₃ are coefficients. 7. The BIM-based project schedule management system according to claim 6, characterized in that: the model graphic element data structure of the three-dimensional information model of the power grid includes basic data and extended data, wherein the basic data includes geometric data, physical data and function Data, extended data includes technical data, economic data and management data. 8. The project progress management system based on BIM according to claim 7, characterized in that: said real-time model includes the statistical distribution of the operation duration, and the statistical distribution includes normal distribution, beta distribution, uniform distribution and triangular distribution, positive In the state distribution, the mean, median, and mode of the process duration overlap, the probability of the process duration being greater than or less than the mean value is equal, and the probability of the process being delayed or advanced is equal. In the Beta distribution, the distribution range is in [0, 1 ], the distribution formula of the Beta distribution is as follows: (1) mean value:

(2) Variance:

The value range of α and β is 0:0.1:10000, and the value range of the mean value is 0.3:0.05:0.5. The simulation results are stored in the matrix respectively. The first column is the α value, the second column is the β value, and the third column is the β value. are listed as variance values. 9. The BIM-based project schedule management system according to claim 8, characterized in that: in the Beta distribution, the safe time is taken as the duration between the duration of the process at 95% completion probability and the duration at 50% completion probability Poor, the formula is as follows: T _k ＝[F(x)I _x＝0.95 -F(x)I _x＝0.5 ]×t _k In the formula, F(x) is the distribution function of Beta distribution, T _k is the safety time of process k, and t _k is the duration of process k. 10. An application of the BIM-based project schedule management system according to any one of claims 1-9, characterized in that: the schedule management system is applied to substation construction simulation project management, and based on the D3Station platform, the analysis of the model is realized And visual display, and support viewing the properties of the model.

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