Three Dimension Terrain Generation Based On Fractal And Simplification Using Multi-resolution LOD

Realistic rendering of 3D terrain scenes has two aims, which are reality of rendering and real-time of rendering. It should maintain higher interactive frame rates without noticeably degrading image quality. However, Virtual reality communities and other visualizations have always faced the problem that their "desirable" visualization dataset sizes are much larger than what the hardware can display at interactive rates. Thus Realistic rendering of 3D terrain scenes is a challenging subject.The 3D terrain visualization based on fractal theory and multi-resolution LOD algorithm is applied in the virtual reality of large-scale 3-D terrain scene simulator in this article.Firstly, the research actuality about 3-D fractal terrain generation and multi-resolution LOD algorithm is summarized.Secondly, the method of 3-D fractal terrain generation is studied.A modified calculating method of the random offset is proposed which speeds up the terrain generation.As the position and height can't be predicted and controlled in the MPD algorithm, two advanced MPD algorithms are proposed according to the practical need for limited peak parameters.A MPD terrain generation algorithm based on mixed elliptical paraboloid is discussed. By using weighed offset mixing algorithm, elliptical paraboloid with adjustable parameters and fractal terrain generated by MPD method is mixed and fractal terrain with controllable shape is gained. Experiment results shows that this algorithm is fast and has good controllability in the shape of terrain.Then, the method of DEM compress using M-band wavelet is introduced. DEM data is simplified by both 2-band wavelet transformation and M-band wavelet transformation, the results show that the later has higher precision when the compress rate is the same.Two new node evaluation criterions are proposed, which improved the view-dependent algorithm based on local entropy. The superiority of simplification speed is proved by experiments.Finally, kinds of parameters are designed in manual walkthrough so that different view methods can be selected; the terrain reality is enhanced by using texture mapping, and the dynamic real time display of 3-D terrain is achieved.