Fast Viewshed Analysis Techniques For Complex 3D Scenes

Visibility refers to the degree of inter visibility of the observer's viewpoint to other spatial target points.The collection of all visible target points constitutes the viewshed under the current viewpoint.Viewshed analysis is an indispensable content in spatial analysis and is an important part of geospatial cognitive research.It is widely used in path planning,missile penetration,landscape analysis,communication base station positioning and other fields.With the continuous development of surveying and mapping technology and the continuous enrichment of GIS data,3D scenes are becoming more and more complex.The comprehensive demand for technology,analysis effects and scene applications make the rapid viewshed analysis of complex 3D scenes become a current research hotspot.The rapid viewshed analysis of complex 3D scenes is of great significance to geospatial environment perception and decision support capabilities.The traditional viewshed analysis technology has problems such as "unavailable,difficult to use,and dare not use" in the application of complex 3D scenes,which seriously restricts the practical application of viewshed analysis.The thesis takes complex 3D scenes as objects and "available,easy to use,dare to use" as the goal to study the rapid viewshed analysis technology of complex 3D scenes,which has important practical application value."Fast" in the thesis refers to further improving the analysis efficiency under the premise of ensuring the accuracy of the algorithm and the credibility of the results,to achieve the effect of human-computer interaction and real-time analysis.The main work of the thesis is as follows:1.In view of the chunk distortion in the traditional viewshed analysis algorithm XDraw based on regular grid DEM,this paper proposes a fast viewshed analysis method for regular grid DEM based on contribution point screening.The paper first analyzes the reason for the chunk distortion caused by the XDraw algorithm,and then records all the contribution points that affect the visibility judgment through an auxiliary grid structure.In the visibility judgment,the contribution points that are too far from the line of sight are excluded,which effectively improves the calculation accuracy of the XDraw algorithm.Experiments show that while this algorithm guarantees a comparable calculation speed,the error rate is reduced by 65% compared with the original algorithm.2.Aiming at the problems of self-shadow artifacts,crawling artifacts and light leakage artifacts in the viewshed analysis application of the post-processing shadow map algorithm,this paper proposes a fast viewshed analysis method for complex 3D scenes based on cascading shadow maps.By constructing multiple layers of nested light source cones,the sampling density of the horizontal 3D scenes is encrypted;a camera depth cone setting based on linear depth is used to improve the distance resolution of the scene.Experiments show that the algorithm effectively suppresses self-shadow artifacts,significantly improves the accuracy of viewshed analysis,and achieves the calculation speed of real-time interaction.3.The thesis designs and implements a rapid viewshed analysis prototype system for complex 3D scenes based on the Cesium platform,and realizes the demonstration application of the viewshed analysis algorithm in 3D Web GIS.First the paper introduces the Cesium open source platform architecture based on the B/S framework;then designs functional modules such as scene loading,cache management,rendering scheduling,and constructs complex 3D scenes;and finally realizes the interactive application of fast viewshed analysis for regular grid DEM based on contribution point screening and interactive application of rapid viewshed analysis of complex 3D scenes based on cascading shadow maps.