Study On Large-scale Virtual Scene Real-time Simulation Technology

Real-time simulation of large-scale virtual scene is one of the key techniques of digital earth, as well as the foundation of the military environment simulation applications. And it is also one of the important propositions of geographic information system (GIS) that must be solved in its course of development toward 3D GIS and VR GIS.Real-time simulation for a simple scene, which includes only hundreds of polygons and dozens MBs of low-resolution textures, is achievable. But a large-scale and complex virtual scene has thousands or even millions of polygons and hundreds MBs of high-resolution textures, and the shading, anti-aliasing and texture mapping are also needed for the whole scene. Then the system appears serious overloaded, the frame rate is decreasing, and the real-time simulation effects of virtual scene are greatly reduced. Adopting the advanced hardware equipments will help to solve this problem, but there is often a conflict between the excessive data and the limited hardware resources. It is necessary to develop new algorithms for optimizing the data structure of the scene, improving the efficiency of memory usage and speeding up real-time display.The representation and real-time simulation of large-scale virtual scene is studied and experimented on a Silicon Graphics multiprocessor, Onyx 3200, with four MIPS R12000 processors and Infinite Reality3 graphic accelerator, under IRIX 6.5 operating system. Taken the Poyang Lake region as test site, we firstly build the LOD models (including terrain and culture feature data) based on viewpoint. Secondly, we adopt Active Surface Definition, a real-time framework, to manage the terrain data, and then apply Clip Texture to efficiently manage the high-resolution textures. Thirdly, the parallel processing technology is used to deploy the scene database dynamically andoptimize real-time simulation graphics, which result in higher fidelity and better simulation effects in the virtual scene we finally built up. And the problem mentioned above is solved effectively. Lastly we develop a corresponding real-time simulation application named Jennie, realize basic functionalities of natural virtual environment of test site, such as real-time display, interaction and walk through etc, and test and analyze the performance. The results show that the database hierarchy of the whole virtual scene is more effective and more proper, and that the real-time display efficiency and simulation effects also have been improved. The fixed frame rate which generally amounts to 50-60 frames/second can be achieved, at least 20 frames/second.