CN112035433B - Method for converting BIM model into GIS model supporting hierarchical loading of large quantities - Google Patents
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Abstract
The invention discloses a method for converting a BIM model into a GIS model supporting hierarchical loading of a large amount, which comprises the steps of constructing a database table of the BIM model; constructing a three-dimensional earth scene structure and analyzing component information; grouping three-dimensional earth scenes; constructing a sub-scene space hierarchical structure, and screening, simplifying and merging data; converting the BIM model into B3DM specifications, wherein each B3DM file is a tile; and constructing a tree space structure of the tile set according to the octree. The invention adopts the mode of secondary development of BIM design software to directly extract the information of the model component, thereby preventing the information from losing; the 3dtiles format of the OGC community standard is adopted as the GIS model format, the hierarchical loading of the mass models is supported through the HLOD technology, the automatic conversion from the BIM model to the HLOD hierarchical loading GIS model is realized, and the method has the advantages of higher conversion speed, higher accuracy and the like, and is convenient for practical popularization and application.
Description
Technical Field
The invention belongs to the technical field of geospatial information systems, and particularly relates to a method for converting a BIM model into a GIS model supporting hierarchical loading of a large amount.
Background
With the development of computer technology and network technology, integration of building information models (Building Information Modeling, BIM) and geographic information systems (Geographic Information System, GIS) at the Web end has become a technical focus of attention in all the communities. From the information contained in the two, the GIS focuses on a large-scale macroscopic environment, the BIM focuses on microscopic information in a building, and the two have a complementary relationship.
The main direction of BIM+GIS research in the current industry is to integrate IFC data into CityGML, and the method has the following problems: 1. IFC and GityGML are data storage and sharing oriented formats, and the IFC and GityGML are required to be translated into a data format which can be rendered by a graphic display card in real time during visualization, so that the problems of overlong loading time, system breakdown and the like of a large model exist. 2. The method for exporting the IFC format file from BIM design software such as Revit and the like has the problems of geometric information loss, semantic information loss and the like at present.
Disclosure of Invention
The present invention has been made in view of the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide a method for converting a BIM model to support a hierarchical loading of a GIS model in a large amount, which can prevent information loss, support a hierarchical loading of a large amount model, and so on.
The technical solution for realizing the purpose of the invention is as follows: a method of converting a BIM model to support a substantially quantitatively hierarchical loading of a GIS model, the method comprising the steps of:
step 1, constructing a database table of a BIM model;
step 2, constructing a three-dimensional earth scene structure, and analyzing component information from a database table;
step 3, grouping three-dimensional earth scenes into sub scenes;
step 4, constructing a sub-scene space hierarchical structure, namely HLOD, and screening, simplifying and merging data according to the geometric errors of each level;
step 5, converting the BIM model coordinates after data processing into a B3DM built-in coordinate specification, wherein each group of data corresponds to a B3DM file, and each B3DM file is used as a tile;
and 6, constructing a tree space structure of the tile set according to the octree to form a GIS model supporting the hierarchical loading of the general quantity.
Further, the building the database table of the BIM model in step 1 specifically includes:
step 1-1, secondary development is carried out through BIM design software, BIM model data are derived from the BIM model data, six empty tables are defined, and the BIM model data, the BIM model files, BIM components, BIM geometric bodies, material mapping and BIM attributes are respectively stored;
step 1-2, analyzing the material information of each geometric surface of the BIM model member, including: illumination parameter information, texture parameter information and material information, wherein the texture parameter information comprises a texture map file; establishing a dictionary for the material information to be cached and reused, and simultaneously storing the texture map file into a material map;
step 1-3, analyzing the triangle mesh information of each geometrical plane of the BIM model component, comprising: obtaining vertexes and adding the vertexes into a vertex array of the geometric triangular net; obtaining a vertex normal, and adding the vertex normal to a normal array of a geometric triangular net; obtaining texture coordinates and adding the texture coordinates into a texture coordinate array of a geometric triangular net; acquiring a triangular surface, and adding vertex indexes to a vertex index array of a geometric triangular net; then the normal vector is extended: each triangular face corresponds to a normal vector or the whole geometric face corresponds to a normal vector;
step 1-4, constructing a geometric object: traversing all geometric surfaces of a geometric body, counting geometric body data, and storing the data into a BIM geometric body surface according to the data specification of the international standard gltf;
step 1-5, analyzing attribute information of the BIM model component, storing attribute names into a BIM attribute table through a dictionary table, storing attribute values into the BIM component table, and associating the attribute names with the BIM attribute table through an attribute ID;
step 1-6, constructing a BIM component structure tree, wherein a root node of the BIM component structure tree is a BIM document model, and then the BIM component structure tree is sequentially provided with elevation, category and component, and the BIM component structure tree is stored in a BIM model scene tree table;
step 1-7, storing BIM components into a BIM component table, and storing BIM model document information into a BIM model file table; the BIM member is an integral combination of several geometries.
Further, the constructing a three-dimensional earth scene structure in step 2, analyzing component information from a database table, specifically includes:
step 2-1, batch loading treatment: acquiring the data size of the geometric body through the BIM component table, and loading the geometric body into a memory according to the preset single-batch data size for processing;
2-2, constructing a three-dimensional earth scene structure in a memory, wherein the three-dimensional earth scene structure comprises scene parameters and 1 or more BIM components, the BIM components comprise an attribute set and a geometric triangular net set, and the triangular net comprises vertexes, normal vectors, texture coordinates, vertex indexes and materials; wherein the scene parameters include a scene shift matrix, a grouping mode, and a grouping size threshold;
step 2-3, triangular network analysis: the gltf data is read from the BIM geometric body surface for analysis, and in the process, if a matrix exists in the BIM component, matrix change is needed to be carried out on vertex and normal vector data; the matrix is a non-identity matrix.
Further, the grouping of the three-dimensional earth scene in step 3 is divided into sub-scenes, which specifically includes:
step 3-1, 1 parent scene is constructed: traversing all triangular meshes in the three-dimensional earth scene and adding the triangular meshes into the parent scene; calculating the maximum geometric error and the minimum geometric error of each triangular net respectively, wherein the minimum geometric error takes the minimum value of the minimum size of the triangle and (triangle texture map pixel coordinate size x map geometric error ratio), and the maximum geometric error takes the radius of the bounding box; counting the data size, bounding box, maximum geometric error and minimum geometric error of the whole father scene;
step 3-2, parent scene block grouping processing: if the data volume in the parent scene is smaller than the preset maximum value of the slice file, not dividing; if only 1 triangle net exists, or the block granularity is 'object' and all triangle nets in the parent scene belong to 1 geometric object, or the block granularity is 'network' and only 1 material in the parent scene, no block is generated any more; otherwise, executing the next step;
step 3-3, dividing the sub-scene according to the materials: counting the related data quantity of each used material in the parent scene, dividing the parent scene into 2 sub-scenes according to the data quantity, and counting and updating the data quantity, bounding box, maximum geometric error and minimum geometric error of the 2 sub-scenes; the relevant data volume of the material includes the data volume of the material itself and the geometric data volume of all grids referencing the material.
Further, the step 3-3 may be replaced with:
dividing sub-scenes by space: according to the octree structure, the space is divided into eight by the bounding box of the father scene, meanwhile, the grids in the father scene are belonged to 8 sub-scene spaces according to the space relation, the data of the 8 sub-scene spaces are updated, and the data size, the bounding box, the maximum geometric error and the minimum geometric error of each sub-scene are counted.
Further, the constructing a sub-scene space hierarchy structure, i.e. HLOD, in step 4, and filtering, simplifying and merging the data according to the geometric errors of each level specifically includes:
step 4-1, constructing a sub-scene space hierarchy structure, namely HLOD: calculating the minimum geometric error of each group, namely the sub-scene, wherein the error is the minimum value in the minimum geometric errors of all triangular networks in the group; calculating the maximum geometric error of each group, namely the sub-scene, wherein the error is the maximum value of the maximum geometric errors of all triangular networks in the group; then, interpolation is carried out between the maximum geometric error and the minimum geometric error through the geometric error decrementing coefficient, and the geometric error of each LOD level is obtained;
step 4-2, screening the triangular network under a certain geometric error level: if the current geometric error is larger than the radius of the bounding box of the triangular surface, the triangular surface is screened out, namely the triangular surface is invisible; otherwise, adding vertex data and index data of the triangular surface to a new simplified triangular network array;
step 4-3, simplification of the triangle network under a certain geometrical error level: if the current geometric error is smaller than the minimum geometric error of the triangular surface or the number of triangles is smaller than a preset threshold value, the method is not simplified; otherwise, simplifying the triangular net by adopting a secondary edge folding and extracting algorithm;
step 4-4, packaging the triangular network under a certain geometric error level: merging the simplified texture maps according to the texture scaling ratio under the current geometric error; removing the same material and packaging the material; vertex, normal vector, texture coordinates, index data of geometry referencing the same material are merged.
Further, in step 5, the BIM model after data processing is converted into a built-in coordinate specification of B3DM, each group of data corresponds to a B3DM file, and each B3DM file is used as a tile, which specifically includes:
step 5-1, the model coordinates+the position of the origin of the model in a certain spatial reference coordinate system = the coordinate P in the spatial reference coordinate system;
step 5-2, transforming the coordinate P into longitude and latitude coordinates LBH, namely coordinates in the earth geodetic coordinate system by using geographic projection transformation;
step 5-3, converting LBH into Cartesian coordinate G by using Cartesian coordinate definition of the processor;
step 5-4, solving a Cartesian coordinate center point C in the current group;
step 5-5, calculating the vertex coordinate p stored in the actual gltf in the B3DM, wherein the vertex coordinate p is p=G-C according to a formula;
step 5-6, calculating an absolute matrix M in the current tile by using a Cartesian coordinate center point C in the current group, wherein p is represented by M=G according to a formula;
step 5-7, calculating a transformation matrix T to be stored in the current tile, wherein the transformation matrix T is as follows: p (T of current tile) (T of parent tile) × … (T of root tile) =g.
Further, in step 6, a tree space structure of a tile set is constructed according to an octree to form a GIS model supporting hierarchical loading of a large amount, which specifically includes:
step 6-1, expanding bounding boxes of all tile tiles to obtain bounding boxes containing all tile contents, and setting the bounding boxes as bounding boxes of tree root nodes;
step 6-2, adding all tiles to the tree root node, and if the radius of the tile bounding box is greater than 1/2 of the radius of the tree root node bounding box, making the tile bounding box fall into the tree root node; otherwise, the central point of the tile bounding box falls to one of eight primary child nodes of the tree root node in space;
step 6-3, further judging whether the child node falling to the step 6-2 falls into the node or a child node falling to the node according to the mode of the step 6-2; repeating the steps 6-2 to 6-3 until all tiles are traversed.
A system for converting a BIM model to support a substantially quantitatively hierarchical loading GIS model, the system comprising:
a first unit for constructing a database table of the BIM model;
the second unit is used for constructing a three-dimensional earth scene structure and analyzing component information from a database table;
a third unit for grouping three-dimensional earth scenes into sub-scenes;
a fourth unit, configured to construct a sub-scene space hierarchy, i.e. HLOD, and screen, simplify and merge data according to the geometric error of each level;
a fifth unit, configured to convert the BIM model coordinates after data processing into a B3DM internal coordinate specification, where each group of data corresponds to a B3DM file, and each B3DM file is used as a tile;
and a sixth unit for constructing a tree space structure of the tile set according to the octree to form a GIS model supporting the hierarchical loading of the general quantity.
A computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, the processor implementing the following steps when executing the computer program:
step 1, constructing a database table of a BIM model;
step 2, constructing a three-dimensional earth scene structure, and analyzing component information from a database table;
step 3, grouping three-dimensional earth scenes into sub scenes;
step 4, constructing a sub-scene space hierarchical structure, namely HLOD, and screening, simplifying and merging data according to the geometric errors of each level;
step 5, converting the BIM model coordinates after data processing into a B3DM built-in coordinate specification, wherein each group of data corresponds to a B3DM file, and each B3DM file is used as a tile;
and 6, constructing a tree space structure of the tile set according to the octree to form a GIS model supporting the hierarchical loading of the general quantity.
A computer readable storage medium having stored thereon a computer program which when executed by a processor performs the steps of:
step 1, constructing a database table of a BIM model;
step 2, constructing a three-dimensional earth scene structure, and analyzing component information from a database table;
step 3, grouping three-dimensional earth scenes into sub scenes;
step 4, constructing a sub-scene space hierarchical structure, namely HLOD, and screening, simplifying and merging data according to the geometric errors of each level;
step 5, converting the BIM model coordinates after data processing into a B3DM built-in coordinate specification, wherein each group of data corresponds to a B3DM file, and each B3DM file is used as a tile;
and 6, constructing a tree space structure of the tile set according to the octree to form a GIS model supporting the hierarchical loading of the general quantity.
Compared with the prior art, the invention has the remarkable advantages that: 1) The BIM design software is adopted to directly extract BIM model component information in a secondary development mode, so that the problems of geometric information loss, semantic information loss and the like of the BIM model in the conversion process are solved; 2) The 3dtiles format of the OGC community standard is adopted as a GIS standardized model format, and hierarchical loading of a large quantity of models is supported through an HLOD technology, so that the problems of overlong loading time, system breakdown and the like of a BIM large model are solved; 3) The conversion method has the advantages of higher conversion speed and higher conversion accuracy, and is convenient for practical popularization and application.
The invention is described in further detail below with reference to the accompanying drawings.
Drawings
FIG. 1 is a flow chart of a method of converting BIM models to support a substantially hierarchical loading GIS model in one embodiment of the invention.
FIG. 2 is a diagram illustrating a display of BIM model conversion results (without overlaying GIS layer data) in a browser according to one embodiment.
Fig. 3 is a schematic diagram of display (overlaying a GIS remote sensing image map) of a BIM model conversion result in a browser in an embodiment.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application will be further described in detail with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the present application.
It should be noted that, if there is a description of "first", "second", etc. in the embodiments of the present invention, the description of "first", "second", etc. is only for descriptive purposes, and is not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include at least one such feature. In addition, the technical solutions of the embodiments may be combined with each other, but it is necessary to base that the technical solutions can be realized by those skilled in the art, and when the technical solutions are contradictory or cannot be realized, the combination of the technical solutions should be considered to be absent and not within the scope of protection claimed in the present invention.
In one embodiment, in connection with fig. 1, there is provided a method of converting a BIM model to support a substantially quantitatively hierarchical loading GIS standardized model, the method comprising the steps of:
s1, constructing a database table of a BIM model;
s2, constructing a three-dimensional earth scene structure, and analyzing component information from a database table;
s3, grouping three-dimensional earth scenes into sub scenes;
s4, constructing a sub-scene space hierarchical structure, namely HLOD, and screening, simplifying and merging data according to the geometric errors of each level;
s5, converting the BIM model coordinates after data processing into a B3DM built-in coordinate specification, wherein each group of data corresponds to a B3DM file, and each B3DM file is used as a tile;
and S6, constructing a tree space structure of the tile set according to the octree to form a GIS model supporting the hierarchical loading of the general quantity.
Further, in one embodiment, the constructing a database table of the BIM model in step S1 specifically includes:
s1-1, secondary development is carried out through BIM design software, BIM model data are derived from the BIM model data, six empty tables are defined, and the BIM model data, the BIM model files, BIM components, BIM geometries, material maps and BIM attributes are respectively stored;
preferably here, the BIM design software employs Revit. And data export is carried out on the Revit three-dimensional model through a Revit SDK API, and the BIM model component is completely extracted to the SQLite intermediate database file. Since SDK provided by Revit's secondary development official is NET frame language, and a large number of C++ open source computing libraries are needed in the process of generating 3DTiles data, the problem of crossing between development languages exists, and a file database is used as an intermediate transition mode, so that a lighter SQLite database is selected.
Step S1-2, analyzing the material information of each geometric surface of the BIM model component, comprising the following steps: illumination parameter information, texture parameter information and material information, wherein the texture parameter information comprises a texture map file; establishing a dictionary for the material information to be cached and reused, and simultaneously storing the texture map file into a material map;
here, the illumination parameter information includes gloss, smoothness, reflectance, shiness, and the like; texture parameter information also includes texture scaling, texture offset, etc.; the texture information includes texture appearance display colors and the like.
Step S1-3, analyzing the triangular mesh information of each geometric surface of the BIM model component, wherein the step comprises the following steps: obtaining vertexes and adding the vertexes into a vertex array of the geometric triangular net; obtaining a vertex normal, and adding the vertex normal to a normal array of a geometric triangular net; obtaining texture coordinates and adding the texture coordinates into a texture coordinate array of a geometric triangular net; acquiring a triangular surface, and adding vertex indexes to a vertex index array of a geometric triangular net; then the normal vector is extended: each triangular face corresponds to a normal vector or the whole geometric face corresponds to a normal vector;
it should be noted here that each component comprises 1 or more geometries, each geometry comprising a plurality of geometrical faces.
Step S1-4, constructing a geometric object: traversing all geometric surfaces of a geometric body, counting geometric body data, and storing the data into a BIM geometric body surface according to the data specification of the international standard gltf;
here, the vertex position stored in gltf is an offset distance from the geometric bounding box center.
S1-5, analyzing attribute information of the BIM model component, storing attribute names into a BIM attribute table through a dictionary table, storing attribute values into the BIM component table, and associating the attribute names with the BIM attribute table through an attribute ID;
here, the attribute information includes basic attributes including family category, family type information, and other attributes including area, volume, top offset, bottom offset, and the like.
S1-6, constructing a BIM component structure tree, wherein a root node of the BIM component structure tree is a BIM document model, and then the BIM component structure tree is sequentially provided with elevation, category and component, and the BIM component structure tree is stored in a BIM model scene tree table;
s1-7, storing BIM components into a BIM component table, and storing BIM model document information into a BIM model file table (BIM models with external links can store a plurality of documents); the BIM member is an integral combination of several geometries.
Here, in general, BIM members have only 1 geometry.
Further, in one embodiment, the constructing a three-dimensional earth scene structure in step S2 includes parsing component information from a database table, and specifically includes:
step S2-1, batch loading processing: acquiring the data size of the geometric body through the BIM component table, and loading the geometric body into a memory according to the preset single-batch data size for processing;
here, preferably, the preset single batch data size is 500M.
S2-2, constructing a three-dimensional earth scene structure in a memory, wherein the three-dimensional earth scene structure comprises scene parameters and 1 or more BIM components, the BIM components comprise an attribute set and a geometric triangular net set, and the triangular net comprises vertexes, normal vectors, texture coordinates, vertex indexes and materials (including texture chartlets); wherein the scene parameters include scene shift matrix, grouping mode, grouping size threshold, etc.;
step S2-3, triangular network analysis: the gltf data is read from the BIM geometric body surface for analysis, and in the process, if a matrix exists in the BIM component, matrix change is needed to be carried out on vertex and normal vector data; the matrix is a non-identity matrix. Here, matrix change refers to storing vertex, normal vector data in matrix form.
Further, in one embodiment, the grouping of the three-dimensional earth scene in step S3 is divided into sub-scenes, which specifically includes:
step S3-1, 1 parent scene is constructed: traversing all triangular meshes in the three-dimensional earth scene and adding the triangular meshes into the parent scene; calculating the maximum geometric error and the minimum geometric error of each triangular net respectively, wherein the minimum geometric error takes the minimum value of the minimum size of the triangle and (triangle texture map pixel coordinate size x map geometric error ratio), and the maximum geometric error takes the radius of the bounding box; counting the data size, bounding box, maximum geometric error and minimum geometric error of the whole father scene;
step S3-2, parent scene block grouping processing: if the data volume in the parent scene is smaller than the preset maximum value of the slice file, not dividing; if only 1 triangle net exists, or the block granularity is 'object' and all triangle nets in the parent scene belong to 1 geometric object, or the block granularity is 'network' and only 1 material in the parent scene, no block is generated any more; otherwise, executing the next step;
preferably here, the grouping threshold is 2MB by default, and the amount of data contains texture.
Here, the grouping threshold defines the size of the largest single b3 dm; if too large, the request is slow and easy to fail, if too small, the request is too much; the intranet is generally 2 MB; if the external network can consider lowering this threshold.
Step S3-3, dividing the sub-scene according to the materials: counting the related data quantity of each used material in the parent scene, dividing the parent scene into 2 sub-scenes according to the data quantity, and counting and updating the data quantity, bounding box, maximum geometric error and minimum geometric error of the 2 sub-scenes; the relevant data volume of the material includes the data volume of the material itself and the geometric data volume of all grids referencing the material.
Here, the step S3-3 may be replaced with:
dividing sub-scenes by space: according to the octree structure, the space is divided into eight by the bounding box of the father scene, meanwhile, the grids in the father scene are belonged to 8 sub-scene spaces according to the space relation, the data of the 8 sub-scene spaces are updated, and the data size, the bounding box, the maximum geometric error and the minimum geometric error of each sub-scene are counted.
Further, in one embodiment, the constructing a sub-scene space hierarchy structure in step S4, that is, HLOD, and filtering, simplifying and merging the data according to the geometric error of each level specifically includes:
step S4-1, constructing a sub-scene space hierarchy structure, namely HLOD: calculating the minimum geometric error of each group, namely the sub-scene, wherein the error is the minimum value in the minimum geometric errors of all triangular networks in the group; calculating the maximum geometric error of each group, namely the sub-scene, wherein the error is the maximum value of the maximum geometric errors of all triangular networks in the group; then, interpolation is carried out between the maximum geometric error and the minimum geometric error through the geometric error decrementing coefficient, and the geometric error of each LOD level is obtained;
here, the geometric error reduction coefficient is preferably 0.1.
Step S4-2, screening the triangular network under a certain geometric error level: if the current geometric error is larger than the radius of the bounding box of the triangular surface, the triangular surface is screened out, namely the triangular surface is invisible; otherwise, adding vertex data and index data of the triangular surface to a new simplified triangular network array;
step S4-3, simplification of the triangle network under a certain geometric error level: if the current geometric error is smaller than the minimum geometric error of the triangular surface or the number of triangles is smaller than a preset threshold value, the method is not simplified; otherwise, simplifying the triangular net by adopting a secondary edge folding and extracting algorithm;
here, the preset threshold is preferably 100.
Step S4-4, packaging the triangular network under a certain geometric error level: merging the simplified texture maps according to the texture scaling ratio under the current geometric error (the texture is very small under the larger geometric error); removing the same materials (same color and same texture), and packaging the materials; vertex, normal vector, texture coordinates, index data of geometry referencing the same material are merged.
Here, the steps S4-2 to S4-4 may be performed not in the above order but simultaneously.
Further, in one embodiment, in step S5, the BIM model after data processing is converted into a built-in coordinate specification of B3DM, each group of data corresponds to a B3DM file, each B3DM file is used as a tile (filling data of vertexes, batches, normal vectors, colors, textures, indexes, materials and the like according to the international standard gltf specification, adopting a drago compression algorithm of google for triangle network vertex data, adopting crn compression for texture data, combining FeatureTable, batchTable, and outputting a single B3DM file as a tile), which specifically includes:
step S5-1, the model coordinates+the position of the origin of the model in a certain spatial reference coordinate system = the coordinate P in the spatial reference coordinate system;
s5-2, transforming the coordinate P into a longitude and latitude coordinate LBH, namely, a coordinate in an earth geodetic coordinate system by using geographic projection transformation;
s5-3, converting LBH into Cartesian coordinate G by using Cartesian coordinate definition of a process;
s5-4, solving a Cartesian coordinate center point C in the current group;
step S5-5, calculating the vertex coordinate p stored in the actual gltf in the B3DM, wherein the vertex coordinate p is p=G-C according to a formula;
step 5-6, calculating an absolute matrix M in the current tile by using a Cartesian coordinate center point C in the current group, wherein p is represented by M=G according to a formula;
step S5-7, calculating a transformation matrix T to be stored in the current tile, where m=m of the parent tile and m=m of the parent tile, so recursively calculating the T of the current tile according to the formula: p (T of current tile) (T of parent tile) × … (T of root tile) =g.
Further, in one embodiment, step S6 of constructing a tree-like space structure of a tile set according to an octree to form a GIS model supporting a hierarchical loading of a general volume, specifically includes:
s6-1, expanding bounding boxes of all tile tiles to obtain bounding boxes containing all tile contents, and setting the bounding boxes as bounding boxes of tree root nodes;
s6-2, adding all tiles to the tree root node, and if the radius of the tile bounding box is greater than 1/2 of the radius of the tree root node bounding box, determining that no child node can accommodate all contents when the tile bounding box falls into the tree root node; otherwise, the central point of the tile bounding box falls to one of eight primary child nodes of the tree root node in space;
step S6-3, further judging whether the child node falling to the step S6-2 falls into the node or falls into a certain child node of the node according to the mode of the step S6-2; repeating the steps 6-2 to 6-3 until all tiles are traversed.
In one embodiment, a system for converting a BIM model to support a substantially quantitatively hierarchical loading GIS model is provided, the system comprising:
a first unit for constructing a database table of the BIM model;
the second unit is used for constructing a three-dimensional earth scene structure and analyzing component information from a database table;
a third unit for grouping three-dimensional earth scenes into sub-scenes;
a fourth unit, configured to construct a sub-scene space hierarchy, i.e. HLOD, and screen, simplify and merge data according to the geometric error of each level;
a fifth unit, configured to convert the BIM model coordinates after data processing into a B3DM internal coordinate specification, where each group of data corresponds to a B3DM file, and each B3DM file is used as a tile;
and a sixth unit for constructing a tree space structure of the tile set according to the octree to form a GIS model supporting the hierarchical loading of the general quantity.
Specific limitations regarding the system for converting a BIM model to support a substantially hierarchical loaded GIS model may be found in the above description of the method for converting a BIM model to support a substantially hierarchical loaded GIS model, and will not be described in detail herein. The various modules in the above-described system for converting a BIM model into a support for substantially hierarchical loading of GIS models may be implemented in whole or in part in software, hardware, and combinations thereof. The above modules may be embedded in hardware or may be independent of a processor in the computer device, or may be stored in software in a memory in the computer device, so that the processor may call and execute operations corresponding to the above modules.
In one embodiment, a computer device is provided comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, the processor implementing the steps of when executing the computer program:
s1, constructing a database table of a BIM model;
s2, constructing a three-dimensional earth scene structure, and analyzing component information from a database table;
s3, grouping three-dimensional earth scenes into sub scenes;
s4, constructing a sub-scene space hierarchical structure, namely HLOD, and screening, simplifying and merging data according to the geometric errors of each level;
s5, converting the BIM model coordinates after data processing into a B3DM built-in coordinate specification, wherein each group of data corresponds to a B3DM file, and each B3DM file is used as a tile;
and S6, constructing a tree space structure of the tile set according to the octree to form a GIS model supporting the hierarchical loading of the general quantity.
For specific limitations on each step, reference may be made to the above limitations on the method of converting a BIM model to support a substantially quantitatively hierarchical loading GIS standardized model, which are not repeated here.
In one embodiment, a computer readable storage medium is provided having a computer program stored thereon, which when executed by a processor, performs the steps of:
s1, constructing a database table of a BIM model;
s2, constructing a three-dimensional earth scene structure, and analyzing component information from a database table;
s3, grouping three-dimensional earth scenes into sub scenes;
s4, constructing a sub-scene space hierarchical structure, namely HLOD, and screening, simplifying and merging data according to the geometric errors of each level;
s5, converting the BIM model coordinates after data processing into a B3DM built-in coordinate specification, wherein each group of data corresponds to a B3DM file, and each B3DM file is used as a tile;
and S6, constructing a tree space structure of the tile set according to the octree to form a GIS model supporting the hierarchical loading of the general quantity.
For specific limitations on each step, reference may be made to the above limitations on the method of converting a BIM model to support a substantially quantitatively hierarchical loading GIS standardized model, which are not repeated here.
The display of the BIM model conversion result in the browser (without overlaying GIS layer data) is shown in fig. 2. The display (overlaying the GIS remote sensing image map) of the BIM model conversion result in the browser is shown in fig. 3.
The invention adopts the mode of secondary development of BIM design software to directly extract the information of the model component, thereby preventing the information from losing; the 3dtiles format of the OGC community standard is adopted as the GIS model format, the hierarchical loading of the mass models is supported through the HLOD technology, the automatic conversion from the BIM model to the HLOD hierarchical loading GIS model is realized, and the method has the advantages of higher conversion speed, higher accuracy and the like, and is convenient for practical popularization and application.
The foregoing has outlined and described the basic principles, features, and advantages of the present invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, and that the above embodiments and descriptions are merely illustrative of the principles of the present invention, and various changes and modifications may be made without departing from the spirit and scope of the invention, which is defined in the appended claims. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (6)
1. A method for converting a BIM model to support a substantially hierarchical loading of a GIS model, the method comprising the steps of:
step 1, constructing a database table of a BIM model;
step 2, constructing a three-dimensional earth scene structure, and analyzing component information from a database table;
step 3, grouping three-dimensional earth scenes into sub scenes;
step 4, constructing a sub-scene space hierarchical structure, namely HLOD, and screening, simplifying and merging data according to the geometric errors of each level;
step 5, converting the BIM model coordinates after data processing into a B3DM built-in coordinate specification, wherein each group of data corresponds to a B3DM file, and each B3DM file is used as a tile;
step 6, constructing a tree-shaped space structure of a tile set according to the octree to form a GIS model supporting the hierarchical loading of the general quantity;
the building of the database table of the BIM model in the step 1 specifically includes:
step 1-1, secondary development is carried out through BIM design software, BIM model data are derived from the BIM model data, six empty tables are defined, and the BIM model data, the BIM model files, BIM components, BIM geometric bodies, material mapping and BIM attributes are respectively stored;
step 1-2, analyzing the material information of each geometric surface of the BIM model member, including: illumination parameter information, texture parameter information and material information, wherein the texture parameter information comprises a texture map file; establishing a dictionary for the material information to be cached and reused, and simultaneously storing the texture map file into a material map;
step 1-3, analyzing the triangle mesh information of each geometrical plane of the BIM model component, comprising: obtaining vertexes and adding the vertexes into a vertex array of the geometric triangular net; obtaining a vertex normal, and adding the vertex normal to a normal array of a geometric triangular net; obtaining texture coordinates and adding the texture coordinates into a texture coordinate array of a geometric triangular net; acquiring a triangular surface, and adding vertex indexes to a vertex index array of a geometric triangular net; then the normal vector is extended: each triangular face corresponds to a normal vector or the whole geometric face corresponds to a normal vector;
step 1-4, constructing a geometric object: traversing all geometric surfaces of a geometric body, counting geometric body data, and storing the data into a BIM geometric body surface according to the data specification of the international standard gltf;
step 1-5, analyzing attribute information of the BIM model component, storing attribute names into a BIM attribute table through a dictionary table, storing attribute values into the BIM component table, and associating the attribute names with the BIM attribute table through an attribute ID;
step 1-6, constructing a BIM component structure tree, wherein a root node of the BIM component structure tree is a BIM document model, and then the BIM component structure tree is sequentially provided with elevation, category and component, and the BIM component structure tree is stored in a BIM model scene tree table;
step 1-7, storing BIM components into a BIM component table, and storing BIM model document information into a BIM model file table; the BIM component is an integral combination of a plurality of geometric bodies;
step 2, constructing a three-dimensional earth scene structure, and analyzing component information from a database table, wherein the method specifically comprises the following steps:
step 2-1, batch loading treatment: acquiring the data size of the geometric body through the BIM component table, and loading the geometric body into a memory according to the preset single-batch data size for processing;
2-2, constructing a three-dimensional earth scene structure in a memory, wherein the three-dimensional earth scene structure comprises scene parameters and 1 or more BIM components, the BIM components comprise an attribute set and a geometric triangular net set, and the triangular net comprises vertexes, normal vectors, texture coordinates, vertex indexes and materials; wherein the scene parameters include a scene shift matrix, a grouping mode, and a grouping size threshold;
step 2-3, triangular network analysis: the gltf data is read from the BIM geometric body surface for analysis, and in the process, if a matrix exists in the BIM component, matrix change is needed to be carried out on vertex and normal vector data; the matrix is a non-identity matrix.
2. The method for converting BIM models to support for substantially quantitatively hierarchical loading of GIS models according to claim 1, wherein the grouping of three-dimensional earth scenes in step 3 includes:
step 3-1, 1 parent scene is constructed: traversing all triangular meshes in the three-dimensional earth scene and adding the triangular meshes into the parent scene; calculating the maximum geometric error and the minimum geometric error of each triangular net respectively, wherein the minimum geometric error takes the minimum value of the minimum size of the triangle and (triangle texture map pixel coordinate size x map geometric error ratio), and the maximum geometric error takes the radius of the bounding box; counting the data size, bounding box, maximum geometric error and minimum geometric error of the whole father scene;
step 3-2, parent scene block grouping processing: if the data volume in the parent scene is smaller than the preset maximum value of the slice file, not dividing; if only 1 triangle net exists, or the block granularity is 'object' and all triangle nets in the parent scene belong to 1 geometric object, or the block granularity is 'network' and only 1 material in the parent scene, no block is generated any more; otherwise, executing the next step;
step 3-3, dividing the sub-scene according to the materials: counting the related data quantity of each used material in the parent scene, dividing the parent scene into 2 sub-scenes according to the data quantity, and counting and updating the data quantity, bounding box, maximum geometric error and minimum geometric error of the 2 sub-scenes; the relevant data volume of the material includes the data volume of the material itself and the geometric data volume of all grids referencing the material.
3. The method of converting a BIM model to support a substantially quantitatively hierarchical loading of GIS models according to claim 2, wherein step 3-3 is replaced by:
dividing sub-scenes by space: according to the octree structure, the space is divided into eight by the bounding box of the father scene, meanwhile, the grids in the father scene are belonged to 8 sub-scene spaces according to the space relation, the data of the 8 sub-scene spaces are updated, and the data size, the bounding box, the maximum geometric error and the minimum geometric error of each sub-scene are counted.
4. The method for converting BIM model to support for substantially hierarchical loading GIS model according to claim 1, wherein the constructing the sub-scene space hierarchy structure in step 4, namely HLOD, and screening, simplifying and merging the data according to the geometric errors of each level specifically comprises:
step 4-1, constructing a sub-scene space hierarchy structure, namely HLOD: calculating the minimum geometric error of each group, namely the sub-scene, wherein the error is the minimum value in the minimum geometric errors of all triangular networks in the group; calculating the maximum geometric error of each group, namely the sub-scene, wherein the error is the maximum value of the maximum geometric errors of all triangular networks in the group; then, interpolation is carried out between the maximum geometric error and the minimum geometric error through the geometric error decrementing coefficient, and the geometric error of each LOD level is obtained;
step 4-2, screening the triangular network under a certain geometric error level: if the current geometric error is larger than the radius of the bounding box of the triangular surface, the triangular surface is screened out, namely the triangular surface is invisible; otherwise, adding vertex data and index data of the triangular surface to a new simplified triangular network array;
step 4-3, simplification of the triangle network under a certain geometrical error level: if the current geometric error is smaller than the minimum geometric error of the triangular surface or the number of triangles is smaller than a preset threshold value, the method is not simplified; otherwise, simplifying the triangular net by adopting a secondary edge folding and extracting algorithm;
step 4-4, packaging the triangular network under a certain geometric error level: merging the simplified texture maps according to the texture scaling ratio under the current geometric error; removing the same material and packaging the material; vertex, normal vector, texture coordinates, index data of geometry referencing the same material are merged.
5. The method for converting BIM model to support the hierarchical loading of GIS model according to claim 1, wherein in step 5, the coordinate conversion of BIM model after data processing is performed into a built-in coordinate specification of B3DM, each group of data corresponds to a B3DM file, each B3DM file is used as a tile, specifically comprising:
step 5-1, the model coordinates+the position of the origin of the model in a certain spatial reference coordinate system = the coordinate P in the spatial reference coordinate system;
step 5-2, transforming the coordinate P into longitude and latitude coordinates LBH, namely coordinates in the earth geodetic coordinate system by using geographic projection transformation;
step 5-3, converting LBH into Cartesian coordinate G by using Cartesian coordinate definition of the processor;
step 5-4, solving a Cartesian coordinate center point C in the current group;
step 5-5, calculating the vertex coordinate p stored in the actual gltf in the B3DM, wherein the vertex coordinate p is p=G-C according to a formula;
step 5-6, calculating an absolute matrix M in the current tile by using a Cartesian coordinate center point C in the current group, wherein p is represented by M=G according to a formula;
step 5-7, calculating a transformation matrix T to be stored in the current tile, wherein the transformation matrix T is as follows: p (T of current tile) (T of parent tile) × … (T of root tile) =g.
6. The method for converting BIM model to support for hierarchical loading GIS model according to claim 1, wherein in step 6, a tree space structure of tile sets is constructed according to octree to form a support for hierarchical loading GIS model, specifically comprising:
step 6-1, expanding bounding boxes of all tile tiles to obtain bounding boxes containing all tile contents, and setting the bounding boxes as bounding boxes of tree root nodes;
step 6-2, adding all tiles to the tree root node, and if the radius of the tile bounding box is greater than 1/2 of the radius of the tree root node bounding box, making the tile bounding box fall into the tree root node; otherwise, the central point of the tile bounding box falls to one of eight primary child nodes of the tree root node in space;
step 6-3, further judging whether the child node falling to the step 6-2 falls into the node or a child node falling to the node according to the mode of the step 6-2; repeating the steps 6-2 to 6-3 until all tiles are traversed.
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