Research And Implementation On Real-time Rendering Technology Of Large Scale Terrain

Real-time rendering technology for large scale terrain is becoming a hot field which attracts more and more researchers' attention at present. It has been widely used in simulation of battlefield, VR, landscape programming of city, flood controlling, outdoor games, movie production, etc. The main method for terrain rendering is the terrain multiresolution model (TMRM). Based on TMRM, critical technologies for real-time rendering of large scale terrain which includes TMRM generating technology, real-time rendering technology through streaming, terrain texture management and mapping technology are studied systematically in this thesis and some new results were obtained.There are many algorithms for generating TMRM models. The famous algorithms include Roam, VDPM, Adaptive triangulation based quadtree and the improved algorithms of them, etc. However, the improvement of the present algorithms mainly focus on the selection of data structure which can speed up generation of the TMRM, few works were put into ameliorating the simplification criterion, hi fact, the simplification criterions used by the algorithms at present are constructed with only two elements which are the distance the vertex from the viewpoint and the roughness of terrain expressed by Z coordinate. This simplifying criterion which discards 2 of 3 dimensions of the vertex can not preserve the important features of terrain correctly, and lead to badly distortion of terrain. To resolve this problem, a new simplification criterion according with human vision sensibility is founded. The principium of the simplification criterion is that the light eradiated from surface will attenuate during it's transmission, so the light energy eradiate from the surfaces far from the viewer will become too faintness to attract the viewer's attention, thus the surfaces far from the viewer can be emerged into larger surface, then by combining with the residual light energy and terrain roughness, the new simplification criterion is formed. This simplification criterion can preserve the important features of terrain; reduce terrain distortion and vertex popping during real-time rendering.For processing the large scale (can't load in memory one time) terrain data, there are two type technologies working through streaming, one is that data blocks are paged in on demand at full resolution first, then simplify them, the other is that data blocks are paged in at low level of detail first, then higher levels of detail is paged in incrementally. Because the first technology pages more data than the second one, so researches are focused on the second technology at present. However, the second technology has the following disadvantages: first, data paging and TMRM generating are integrated into one modulate, next, data structures they used are very complicated and large, in addition, the work of data preprocessing is very heavy and frequently data paging need the server with high performance, at last this paging method is very difficult for implementation. As for the first technology, an important advantage of it is that the data paging and TMRM generating are not interdependent, so it will be more easily applied in practice than the second one. As an implementation of the first technology, Lindstrom introduced a method which uses quadtree and triangle binary tree to organizeterrain data and adopt multithread mechanism to realize the data process. However, the data structure used by this method is very large for its dependence on the physical partition of terrain, computation needed for generating the TMRM is also depends on the physical partition of terrain and at the same time, the TMRM can not be generating incrementally by this method. To resolve these problems, we put forward a new method which can realize the real-time rendering of large scale terrain with high performance by working through streaming. By partitioning data block into reasonable size for paging in logically and constructing the TMRM data structure with four quadtrees, this method eliminates the d...