Research On WebGL-based Visualization Technologies Of Large-Scale 3D Scene

As the development of GIS is on the way to 3D and Web, 3D WebGIS has already been a research hotspot. It provides great convenience to people's daily life, and has promising research and application value.However, as a new research area,3D WebGIS still has some shortcomings and defects,such as lack of a unified and efficient B/S-mode framework; 3D spatial data types are so diverse that it is difficult for Web transmission and interoperability; Modeling of large-scale 3D object scene is time-consuming; Ineffcient data organization and scheduling result in that difficult to meet the rendering requireents. To solve the problems above, this article builds a B/S-mode 3D digital earth platform, discuss and realize the key technologies of large-scale 3D scene visualization based on WebGL. The main research work can be concluded as follows:1. Research into WebGL network graphical visualization technology has been made, and on this basis a WebGL-based 3D WebGIS framework which can meet the requirement of large-scale 3D scen visualization is designed.2. To make up for the deficiency that common spatial datas are not available for web visualization, a web-oriented DEM tile structure is designed, and research on a new 3D model format named glTF(gl Transmission Format) which is specially designed for WebGL has been made. MeanWhile,method and procedure which can quickly create large-scale glTF 3D object model scene are proposed;3. To improve the the efficiency of visulazation, algorithms for partition and LOD process of scene datas on webserver are presented, the scene data are ordinally organized by pyramid index, and a quadtree spacial indexing mechanism specially designed for 3D object models is also established; A Horizon culling algorithm apply to Digital Earth and screen error evaluation function are designed to determine the specific range and level of target scene. On this basis, a fast scene data search algorithm is presented.4. A WebGL-based 3D digital earth platform named HigisGlobe is designed and built to achieve the visualization of large-scale 3D scene and to verify the key technologies of this article.