Research On Rendering Of High-precision Terrain Based On Fractal

The visualization and real-time rendering of three-dimension (3D) terrain surface are hot research topics in virtual reality (VR), geographic information system (GIS), computer graphics, scientific computation visualization and other associated fields. With the improvement of computer graphic hardware capability, the algorithm of 3D terrain rendering is going into the period of real-time visualization. Although, many top grade graphic workstations have the capability to rendering thousands upon thousands triangles real-timely, the hugeness terrain data is also the problem against the real-time rendering ability of the general computers. In order to solve contradiction between the speed of rendering and reality of rendering, this paper gives a research in fields of 3D terrain rendering, fractal terrain model, level of detail model and so on. Summarily, the main studies and achievements of thesis are listed as following:Firstly, the development of terrain rendering and the theory of 3D terrain visualization are studied in this thesis. Also, some typical algorithms of terrain rendering such as Vertex-based method, Real-Time Optimally Adapting Meshes (ROAM) and View Dependent Progressive Mesh (VDPM) are compared in this thesis. The author gives the advantages and disadvantages of these algorithms. A new method with different flow is proposed. This new method loads the character parameters of each area from memory with the movement of the viewpoint instead of loading each level of detail model. So, the computing time is cut down and the efficiency of rendering is improved.Secondly, because of complex and randomicity of the nature feature, the reality and randomicity of the terrain can not be rendered with the general interpolation methods. The extending technique of terrain visualization based on fractal theory is presented in this thesis. The specialties of fractal theory are self-similar and illimitably fractionize. So, the fractal theory is used in 3D terrain rendering.Thirdly, analyzing characters of many fractal methods in detail, a new interpolation based on DEM method is proposed. Presently, fractal theory is usually used to construct 3D terrain model with some few control points. These construction methods include Iteration Function System (IFS) interpolation and fractal Brownian motion (fBm) interpolation. The algorithm based on random midpoint displacement is used into continuous level of detail theory because of its realizing simply. This is also an innovation in this thesis.Finally, in order to solve the problem of drape, an improved random midpoint displacement method is proposed. This method increases a new parameter in the random variable. This parameter associates the special characters of each area of terrain.The digital elevation model of Qingjiang is used as example. The result analyzing is proposed in this thesis.