Research And Implementation Of Embedded Systems Three-dimensional Terrain Visualization

The application of three-dimensional terrain visualization is of vital significance in the fields such as military environment simulation, anti-terrorism surveillance, forest-fire prevention and wilderness exploration. At present, this technology has been widely used in PC, laptop, server which is powerful in graphics processing, and thus produced a lot of optimization algorithm. Based on OpenGL engine one can get a superb user experience. With the great universality of mobile terminal and the update of various high-resolution satellite and aerophotogrammetry technology, it has become an urgent demand to achieve the visualization of three-dimensional terrain in embedded mobile terminal. However, embedded devices platform is slow in reading data and not powerful enough in graphics processing. Faced with the great amount of three-dimensional terrain data, the optimization algorithm of ordinary calculator has a poor instantaneity to be applied in embedded mobile terminal, which can not satisfied user needs. Therefore, embedded three-dimensional terrain visualization has become one of the difficult points in the research in this field. This paper is intended to do a research on this problem from terrain model construction, model simplification and terrain rendering algorithm, and it has accomplished the following :(1) It analyzed the research status and problem of the three-dimensional terrain visualization, the relevant theories and methods on terrain visualization, which laid foundation for the generation of three-dimensional scene.(2) Do a research on a model simplification algorithm based on the vertex normal vectors. With the optimization of visual features as its principle, it has a smaller visual impact. But this algorithm is complex and by using it the terrain feature points is prone. To solve this problem, this algorithm has been improved in the thesis. After the improvement, it can decrease the calculation to some degree. And it is applied to the large scale terrain with more nodes, the superiority of the improved algorithm is more obvious to be seen. This paper also does a contrastive analysis on the validity of the improved algorithm.(3) Aiming at the disadvantages of embedded system, such as small memory and limited calculating ability, this paper optimized the LOD drawing algorithm which is based on quad tree terrain. First, it modified the 1+8+16 data scheduling strategy to decrease the data each time scheduled and processed in memory during drawing. Moreover, it used a viewpoint clipping algorithm based on Node Projection which decreased large calculation when estimating the visuality of each node. Last, according to evaluation function of node based on the minimum sight distance, appropriate level of detail model is chosen. All above strategies are aiming at decreasing the amount of triangle in the terrain drawing, reducing the data and increasing the efficiency of terrain drawing.(4) Modular design of system was realized. Try to simulate terrain by using OpenGL ES three-dimensional hardware to accelerated three-dimensional engine library and to simulate terrain by adopting EVC(Embedded Visual C++4.0). By accelerating the collaborative optimization of hardware and software, three-dimensional texture mapping and roaming has been achieved, and the instantaneity of three-dimensional terrain has been increased.