| The city/region scale simulation is becoming a hot topic in recent years. With the development of computer graphics and virtual reality technology, more and more efforts are made for the achievement of a real-time, immersed virtual simulation environment. It is hoped that the virtual scene with better reality and wider range can be observed in a more natural way. Actually, the complexity of the city/region scale scenes is infinite while the handling capacity of any hardware in unit time is limited. In the city/region scale simulation system, lots of data and virtual models need to be processed and the visible culling and collision detection are less efficient. Therefore, different organizing and managing approaches of the virtual scene models directly affect the performance of the system.This thesis participated in the design and achievement of a city/region simulation platform VRGIS (Virtual Reality Geographical Information System). VRGIS platform is a 3D graph engine based on OpenGL, which supports stable and real time navigation of 3D scenes constructed by huge volume date. COM technology is applied for the seamless integration of VR and GIS. VRGIS platform also provides various natural phenomenon simulations, with the advantage such as reality and interaction. VRGIS has passed the Quality Evaluation of National Software Testing Center.Based on the research of the virtual scene organizations and algorithms in existence, this thesis introduces a HBB (Hierarchical Bounding Box) approach to organize and manage model scenes, and uses the HBB structure to optimize the scene structure. In addition, based on the HBB structure, visibility culling, LOD and collision detection in VRGIS simulation platform is achieved. This thesis is the core of virtual scenes organization and management in VRGIS. There are two primary innovations, which are the frustum culling in an artificial intelligence approach and LOD achievement in city/region scenes based on HBB structure. |
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