On The Progressive Mesh Simplification Algorithms In Virtual Environment Based On Lod Technology

With virtual reality technology development in the application of military simulation, virtual battlefield environment simulation on the system has gradually in the military exercises and training in peacetime use. In the virtual battlefield environment simulation system, on the one hand it needs to be very realistic exquisite image quality, on another hand it meets the real-time interactive operation, not letting users have a discontinuity feeling. It is requires not only guarantee a good image quality but also ensure the exchange of real-time methods to achieve. The thesis mainly studies both progressive mesh formation and mesh simplification related to view-dependent based on LOD (Level of Detail, LOD) technology in-depth.The basic concepts, primary characters and key techniques of virtual reality are described firstly. In the same time some methods to accelerate scene rendering are introduced briefly. The significance of studying virtual battlefield environment simulation is pointed out. Then a systematic survey on LOD technology is introduced, which includes the concepts, the research content and main algorithms of a number of LOD. The thesis comes from two aspects as follows:This thesis proposes and implements a new progressive mesh simplified method. In this method, edge collapse is also mesh simplification-based operation. The cost of edge collapse is measured by the product of the edge length and surface curvature and quadric error metric which is easy to be estimated and can reflects geometric character of the meshmodel.The collapse adage is chosen based on the principle of the least cost of the edge collapse, and the objective vertices genera led by edge collapsing are confined to the subset of the original mesh vertices, so geometric information of new vertex needs not to best stored The experimental results indicate that this algorithm is easy to implement, runs fast and occupies small storage. Moreover it can guarantee a high resemblance of the geometric characters between the simplified model and the original model.For large mesh model, in accordance with different view-dependent to describe different details, we aimed to improve Hoppe's BSP tree structure. The new algorithm decreases the number of nodes. So the cost of search and store is decreasing. In pre-process, only one time calculation can finish the model simplification. From test result, the improved algorithm uses less time in making BSP tree structure. It needs not to re-construct the BSP tree. When the level of scene is changing, the drawing-time is the real-time. The new algorithm has much more real-time characteristic. So the mesh simplification of view-dependent is adaptive to simplify large three-dimensional mesh model.