Modeling And Rendering Of Surface Targets And Terrain Based On LOD

Mergence of surface targets and terrain is important to the sense of reality of three-dimensional virtual environment. In the terrain interactive simulation applications, viewpoint is close to the ground, so the requirements of merging accuracy of surface targets and terrain is higher. However, in the actual development process, the surface targets and terrain model is often modeled by different modeling software, accompanied by different data structure and organization, leading to imprecise mergence between surface targets and terrain. Therefore, whether it is from the visualization point of view or from the accurate positioning, query analysis, the merging implementation of surface targets model and terrain model , in particular, mergence in the data-level between the targets model dependent on the terrain mesh and terrain model is the most pressing problem.There are two obvious problems in present mergence program: First, the majority of current mergence programs are based on the terrain constructed by Triangulated Irregular Network, mergence of targets and terrain model based on regular square grid is rarely mentioned. Second, different modeling ways, data structure and data organization leading to mergence difficulties. In this paper, by reviewing the commonly used modeling methods of terrain and common three-dimensional targets and key technologies in virtual landscape simulation, provides a model preparation for the mergence. According to the topographic relationship of surface targets and terrain, put forward mergence program about targets model independent of terrain and terrain model, as well as mergence program about targets model dependent on terrain and terrain model. The mergence algorithms for both types of targets have been studied, mainly include the following aspects:(1) Proposed a method of constructing multi-resolution model by extending resolution of the changing cells, combining view-dependent LOD simplification techniques and descripting the contour with smaller triangles.(2) Resolved the cracks problem led by different resolutions of the adjacent cells adopting increasing transition region. According to the way of avoiding cracks between terrain blocks, introducing window scanning technique, solve problem of vertex active status interaction between the adjacent cells. Finally, at different thresholds, make data statistics and comparative analysis about the increase number of triangles and LOD generation time of terrain model merged with road. In accordance with the methods of accuracy evaluation proposed in this paper, make statistics about road border triangle vertexs'plane position deviation from road border. Statistics indicated that in the choice of a suitable threshold condition, mergence effect of this method is realistic and has smaller impact on real-time rendering of terrain.