Research On Key Technologies Of Rapid Simplification Of 3D Building Model

The increasing complexity and data density of 3D digital model bring great pressure on computer storage,display,transmission and rendering.The construction of complex scenes of three-dimensional cities often requires the use of massive multi-source and heterogeneous spatial data,and the three-dimensional building model is an indispensable element.In order to obtain building models suitable for a variety of scenes,it is necessary to establish different Level Of Detail models(level of detail,LOD)for the original high-resolution mesh model.How to quantitatively optimize the level of detail of LOD model according to the different complexity of the model,keep the important features adaptively and reduce unnecessary redundancy,so as to conform to the level of human cognitive process,is an important technical content of Web3 D display.The establishment of LOD model is faced with the problem of mesh simplification.The mesh simplification method is to reduce the computational complexity of the complex model by conditionally reducing the secondary details on the premise of preserving the important geometric and visual features of the model.The common mesh simplification algorithms are classified by simplification mechanism,which can be divided into incremental simplification represented by Schroeder et al.(1992),vertex clustering represented by rossignac et al.(1993),and polygon surface reconstruction represented by Turk et al.(1992)Sampling and loop(1987)propose adaptive subdivision,which is represented by triangle based smooth surface subdivision.Other algorithms include the image-based simplification algorithm proposed by Lindstrom et al.(2000),and the wavelet decomposition simplification algorithm proposed by DeRose(1997),which is suitable for smooth surface simplification.Among them,edge collapse algorithm belongs to one of incremental simplification,which is fast in calculation and robust in model simplification,but the problem of loss of model details may occur in large-scale simplification.In this paper,based on the study of the current mainstream multi-resolution rendering and 3D model edge folding simplification algorithms and other related technologies,aiming at the problems of visual degradation caused by the reduction of mesh quality and the loss of surface details when 3D complex model is simplified to low resolution.In this paper,a simplified algorithm of edge folding of 3D complex model considering angle error is proposed,and a fast visualization system of urban 3D building model is designed.The main contents of this paper are as follows:(1)In view of the visual degradation caused by the degradation of mesh quality and the loss of surface details when the 3D building model is simplified to low resolution,a mesh edge folding simplification algorithm considering angle error is designed.In order to reduce the number of edges that need to be folded and improve the calculation performance,the algorithm adds the vertex constraint processing in advance when selecting the shrinking edge.On the basis of the quadratic error measurement algorithm,the angle error weighting is introduced to control the rotation direction of the new patch,so as to improve the error measurement of the vertices in the feature area of the model and better retain the surface details of the model ?(2)According to the different characteristics and attribute information of 3D building model data,this paper analyzes the data hierarchy of 3D building model,designs the data structure for 3D building model,organizes and manages the 3D building LOD model generated by the algorithm in this paper,and realizes the gridding storage of 3D building model data by the method of dividing the central coordinates of building model with equal longitude and latitude difference grid In order to improve the index efficiency and network response speed,the pyramid structure is used to store the range data.(3)In view of the above research content,based on the webgl 3D rendering engine,a unified representation system of 3D city scene with practical value is developed.The experiment shows that the algorithm effectively reduces the number of elements drawn by the system on the premise of retaining the important geometric features of the building model in the scene,and is suitable for rendering large-scale 3D city scene.