CN113593032A - Three-dimensional building model edge folding simplified algorithm considering angle error - Google Patents
Three-dimensional building model edge folding simplified algorithm considering angle error Download PDFInfo
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Abstract
The invention discloses an angle error-considered three-dimensional building model edge folding simplified algorithm, which comprises the following steps: the method comprises the following steps: an initialization process: s1: preprocessing an initial model; s2: calculating an error matrix of each vertex; s3: calculating the new vertex position generated by contraction of each edge; s4: putting the edge into a pile, and establishing a minimum pile; s5: calculating an error measurement value of each edge contraction; step two: the process is simplified: s6: taking out the edge of the pile top, and folding the edge; s7: calculating the angle error after folding, and performing angle control; s8: updating the angle error of the edges around the simplified edge, and establishing the minimum pile again; s9: judging whether the simplification requirement is met: if the simplification requirement is not met, the process returns to step S6 to continue to fold downward, and if the simplification requirement is met, the simplification is completed. The invention has reasonable structural design and avoids the possibility of visual degradation caused by the reasons of reduced quality of model grids, loss of surface detail characteristics and the like.
Description
Technical Field
The invention relates to the technical field of three-dimensional building model edge folding, in particular to an angle error-considered three-dimensional building model edge folding simplification algorithm.
Background
With the aging of the three-dimensional laser scanning technology and the upgrading of the three-dimensional data acquisition equipment, the data density of the three-dimensional digital model acquired by people is increasing, but the effect of the method is still to be improved by transmitting massive high-density data through a network to draw a large-scale three-dimensional scene in real time.
The real-time rendering of large-scale three-dimensional scenes requires that high-quality images are rendered on one hand, and the operation requirements of real-time interaction of users are met on the other hand. In order to obtain a detailed model suitable for various scenes, different degrees of simplification operations are required for a high-resolution mesh model. Level Of Detail (LOD) techniques are effective methods for reducing the complexity Of three-dimensional data. How to quantitatively optimize the detail level of the LOD model according to different complexities of the model, adaptively reserve important characteristics and reduce unnecessary redundancy so as to accord with the hierarchy of the cognitive process of people, and the LOD model is important technical content of network three-dimensional display.
The LOD model is built by first facing the problem of mesh simplification. The mesh simplification method is to reduce the secondary details on the premise of keeping the important geometric and visual characteristics of the model so as to reduce the data volume of the model. At present, scholars propose various grid simplifying methods based on different algorithm ideas. Common simplification mechanisms include Vertex clustering (Vertex clustering-ring), Incremental simplification (Incremental simplification), Sampling (Sampling), and Adaptive Subdivision (Adaptive Subdivision), and the simplification algorithm basically adopts some combination or deformation of the four mechanisms. The edge folding algorithm belongs to one of incremental simplification, and the essence of the edge folding algorithm is vertex deletion. The algorithm has the excellent characteristics of good quality and robustness of the simplified model, capability of greatly simplifying, generation of models with different precisions, easiness in seamless switching among LODs of different levels and the like.
Hoppe first simplified the mesh model in 1993 using an edge folding method, which determines the order of edge folding and the position of new vertices by optimizing a global energy equation, and generates simplified models of different complexity by adding details one by one. The quality of a result model generated by the algorithm is good, but the calculation process is nonlinear, and the realization and the use are difficult. In 1998, Garland et al proposed a Quadratic Error Metric (QEM) edge folding algorithm based on the Hoppe algorithm, which takes the sum of squared distances from a new vertex to a First-Order neighborhood Triangle (FOT) as an Error in the Error metric, and the calculation process is simple, but the detailed features of the model surface cannot be well maintained. Different from the Garland algorithm, the mesh subdivision method proposed by segment dawn and the like adds the volume error and the triangle flatness into the error measure, and has poor effect of simplifying the boundary triangle; and Liu Xiao Li and the like determine the folding cost according to the sharp feature degree of the vertex on the basis of a QEM simplified algorithm, so that the time complexity is reduced, but a threshold value and a penalty coefficient need to be set according to experience. Director et al introduces the importance of the vertices into the weight of the folding cost to change the folding order of the edges to achieve better results but with longer computation time.
Aiming at the problem of visual degradation caused by the reasons of reduced model grid quality, lost surface detail characteristics and the like when a three-dimensional building model is simplified to a low resolution, the invention designs an angle error-considering three-dimensional building model edge folding simplification algorithm.
Disclosure of Invention
The invention aims to overcome the problems in the prior art and provide an edge folding simplified algorithm of a three-dimensional building model considering angle errors, wherein vertex constraint processing is added in advance when a contraction edge is selected so as to reduce the number of edges needing folding operation and improve the calculation performance; the angular error weighting is introduced on the basis of a quadratic error measure algorithm, and the angular error control is performed on the rotation direction of the generated new patch so as to improve the error measurement of the vertex of the model feature area and better reserve the model surface detail features and visual features, thereby avoiding the possibility of visual degradation caused by the reasons of reduced model mesh quality, lost surface detail features and the like.
In order to achieve the technical purpose and achieve the technical effect, the invention is realized by the following technical scheme:
an angle error-considered three-dimensional building model edge folding simplified algorithm comprises the following steps:
the method comprises the following steps: an initialization process:
s1: preprocessing an initial model;
s2: calculating an error matrix of each vertex;
s3: calculating the new vertex position generated by contraction of each edge;
s4: putting the edge into a pile, and establishing a minimum pile;
s5: calculating an error measurement value of each edge contraction;
step two: the process is simplified:
s6: taking out the edge of the pile top, and folding the edge;
s7: calculating the angle error after folding, and performing angle control;
s8: updating the angle error of the edges around the simplified edge, and establishing the minimum pile again;
s9: judging whether the simplification requirement is met: if the simplification requirement is not met, the process returns to step S6 to continue to fold downward, and if the simplification requirement is met, the simplification is completed.
Preferably, in S1, in the model preprocessing, a vertex constraint process is added in advance when the contraction edge is selected.
Compared with the prior art, the invention has the following beneficial effects:
the invention has reasonable structural design, and comprises the following steps: according to the method, vertex constraint processing is added in advance when a contraction edge is selected in the model preprocessing process through a QEM edge folding simplification algorithm, so that the number of edges needing folding operation is reduced, and the calculation performance is improved;
secondly, the method comprises the following steps: by introducing angle error weighting on the basis of a quadratic error measure algorithm, namely introducing vertex curvature and a triangle normal constraint factor into the error measure, angle error control is carried out on the rotation direction of the generated new patch, the generation of a long and narrow triangle is reduced, so that the error measure of the vertex of a model feature region is improved, and the model surface detail features and visual features are better reserved;
thirdly, the method comprises the following steps: on the premise of retaining the detail characteristics and visual characteristics of the model surface, the density of the three-dimensional model mesh is reduced, most of the geometric characteristics of the building model are retained by a small number of triangular patches, and a simplified model with higher quality is output.
Of course, it is not necessary for any product in which the invention is practiced to achieve all of the above-described advantages at the same time.
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In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a technical roadmap for the present invention;
FIG. 2 is a flow chart of the algorithm of the present invention;
FIG. 3 is a diagram illustrating the overall architecture of a system according to an embodiment of the present invention;
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
Referring to fig. 1-2, an angle error-based simplified edge folding algorithm for a three-dimensional building model includes the following steps:
the method comprises the following steps: an initialization process:
s1: preprocessing an initial model: in the model preprocessing process, vertex constraint processing is added in advance when a contraction edge is selected, so that the number of edges needing folding operation is reduced, and the calculation performance is improved;
s2: calculating an error matrix of each vertex;
s3: calculating the new vertex position generated by contraction of each edge;
s4: putting the edge into a pile, and establishing a minimum pile;
s5: calculating an error measurement value of each edge contraction;
step two: the process is simplified:
s6: taking out the edge of the pile top, and folding the edge;
s7: calculating the angle error after folding, and performing angle control;
s8: updating the angle error of the edges around the simplified edge, and establishing the minimum pile again;
s9: judging whether the simplification requirement is met: if the simplification requirement is not met, the process returns to step S6 to continue to fold downward, and if the simplification requirement is met, the simplification is completed.
Example 2 example of application
The method is applied to an urban three-dimensional scene basic data expression system which is based on WebGIS and B/S framework and faces to actual application scenes.
The system applies the component technology to realize the loose coupling of the architecture, each module has high self-independence, and the modules among all the layers of the system can be flexibly multiplexed, dispersedly combined and expanded. The system is built by using WebGL (Web Graphics library) technology and combining with national standard geographic grids, IIS 8.0 is used as a Web Server, ArcGIS Server 10.6 is used as a GIS Server, PostgreSQL + Postgis is used as a database, page display and spatial information data rendering of a client are carried out through VUE, WebServer and other framework technologies, and the overall architecture of the system is shown in figure 3.
Example 3 application example
By selecting a certain mountain scene in Yunnan province, the number of original triangular faces of the scene is about 4000 ten thousand, the data size is about 1GB, and the scene loading time is about 12 s. The number of the simplified triangular panels is reduced to about 800 ten thousand, the data size is about 213M, the loading completion time is about 3s, and the rendering effect of the three-dimensional building model edge-folding simplification algorithm in a large-scale urban scene is realized.
One specific application of this embodiment is: the three-dimensional building model edge folding simplification algorithm considering the angle error is provided based on the QEM edge folding simplification algorithm, and vertex constraint processing is added in advance when a contraction edge is selected in the model preprocessing process, so that the number of edges needing folding operation is reduced, and the calculation performance is improved;
introducing angle error weighting on the basis of a quadratic error measure algorithm, namely introducing vertex curvature and a triangle normal constraint factor in the error measure, and performing angle error control on the rotation direction of the generated new patch, so that the generation of a long and narrow triangle is reduced, the error measure of the vertex of a model characteristic region is improved, and the surface detail characteristics and the visual characteristics of the model are better reserved;
on the premise of retaining the detail characteristics and visual characteristics of the model surface, the density of the three-dimensional model mesh is reduced, most of the geometric characteristics of the building model are retained by a small number of triangular patches, and a simplified model with higher quality is output.
In the description herein, references to the description of "one embodiment," "an example," "a specific example" or the like are intended to mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
The preferred embodiments of the invention disclosed above are intended to be illustrative only. The preferred embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention. The invention is limited only by the claims and their full scope and equivalents.
Claims (2)
1. The utility model provides a three-dimensional building model limit of considering angle error folds simplified algorithm which characterized in that: the method comprises the following steps:
the method comprises the following steps: an initialization process:
s1: preprocessing an initial model;
s2: calculating an error matrix of each vertex;
s3: calculating the new vertex position generated by contraction of each edge;
s4: putting the edge into a pile, and establishing a minimum pile;
s5: calculating an error measurement value of each edge contraction;
step two: the process is simplified:
s6: taking out the edge of the pile top, and folding the edge;
s7: calculating the angle error after folding, and performing angle control;
s8: updating the angle error of the edges around the simplified edge, and establishing the minimum pile again;
s9: judging whether the simplification requirement is met: if the simplification requirement is not met, the process returns to step S6 to continue to fold downward, and if the simplification requirement is met, the simplification is completed.
2. The three-dimensional building model edge folding simplification algorithm considering the angle error is characterized in that: in the step S1, in the model preprocessing process, vertex constraint processing is added in advance when a contraction edge is selected.
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| CN116721218A (en) * | 2023-07-08 | 2023-09-08 | 南京信息工程大学 | Three-dimensional real estate model light-weight method, system and equipment |
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Application publication date: 20211102 |