Research And Implementation Of Large-scale Spherical Terrain Rendering Technology

"Digital earth" is a virtual earth system which is based on the geographical coordinates to earth, has the massive multi-resolution amounts of data,it can be shown from a different perspective to multi-dimensional. Building a Digital Earth has become the urgent needs of simulation battlefield environment in a military operational command system, the three-dimensional virtual reality maps, geographic information, and many other urban areas. Therefore, this paper will examine how to build and implementation of a large-scale mass data based on multi-resolution, three-dimensional visualization seamless spherical terrain system.To achieve this system, this paper will collect vast amounts of terrain elevation data and terrain texture data, and organize them effectively. By studying the modeling method from a flat terrain system to spherical terrain system,and using existing knowledge and graphics rendering GPU rendering technology to achieve a real-time simulation of digital earth roaming system. The key features about graphics of this paper will be drawn based on real-time, realistic and interactive,we will focus on large-scale multi-resolution spherical terrain LOD rendering techniques, GPU-based rendering acceleration technology to simulate realistic digital earth globe and three-dimensional digital visualization.This paper studies the real-time rendering method for multi-resolution spherical system, generates spherical discrete grid model by modeling the terrain based on the latitude and longitude. Since the Earth is a little flat ellipsoid on the two levels, this paper builds out a resolution LOD global discrete grid model by dividing the digital earth with latitude and longitude, combing quadtree algorithm based tile and the pyramid structure model,which can split quad flat terrain mesh,through combining research from the plane coordinate system to the ellipsoid coordinate spherical coordinate system conversion algorithm. Research and realization of discrete LOD crack treatment spherical grid model, elevation error control and texture as well as the projected area of control and jumping phenomenon which are the key technologies of real-time updates the LOD grid key technologies.In order to increase the efficiency of digital rendering of the Earth, effectively reducing the number of triangles per frame to render, this paper researchs the cones clipping algorithm based on spherical terrain and the visibility culling algorithms which includs back-face culling and occlusion culling. In order to enhance the realism of Digital Earth, the paper also studied how to render spherical terrain by using GPU-accelerated technology, studied and implemented multiple uses anti-aliasing, compressed textures, texture blending and geometry shader-based dynamic high light illumination technology by using the latest specification OPENGL. Combination of these techniques to design a controlled study of three-dimensional digital viewpoint visualization roam the Earth system and the visualization system performance test analysis, the final field with the current graphics hardware and software technologies for digital earth in the field of virtual reality for further outlook.