Studying On Three-Dimension Visualization And Real-Time Rendering Of Terrain

The visualization and real-time rendering of three-dimension (3D) terrain surface are hot research topics in geographic information system (GIS), digital photogrammetry (DP), virtual reality (VR) and other associated fields. This thesis focuses on the theoretical and methodological studies in the several subtopics: (1) digital terrain model (DTM) creation, (2) 3D terrain rendering, (3) fractal terrain simulation, (4) terrain simplification, (5) multiresolution terrain representation, and (6) internet-based terrain visualization. These studies are based on some interdisplines such as 3D computer graphics, computer geometry, scientific computation visualization, virtual reality, and computer network. The goal of this thesis is to build a technological framework for visualization and real-time rendering of 3D terrain surface. The main results of this study are summarized as follows.(1) The method of generating DTM is examined in detail. An optimal algorithm is designed to create a Delaunay TIN with constraint of feature lines.(2) Based on OpenGL library and its work principle, the process of 3D surface rendering is analyzed at length, including modeling, spatial transform, illumination processing, visible area determination, background culling, shading, and texture mapping. Some methods are presented to improve rendering effects and to speed up graphic display. The voxel-based terrain rendering technique is also discussed.(3) On the basis of fractal theory, the terrain simulation is systematically studied and carried out using fractal Brown motion (FBM) method. The physical meaning of two parameters in FBM, H and 5, is pointed out. For the fractal terrain simulation, the "diamond-square" algorithm based on random midpoint displacement (RMD) is given in detail.(4) Data structures and technical properties of some types of multiresolution terrain representation methods are compared and elaborated. A new classification method for multiresolution terrain representation is proposed. The optimization suggestion is given for the real-time optimally adaptingmeshes (ROAM) algorithm. It provides a foundation for the subsequent multiresolution terrain representation research.(5) The basic properties of real-time multiresolution terrain representation are analyzed. To represent dynamic multiresolution terrain in real time, two sorts of models suitable for current stage are proposed, the adaptive quadtree model and the implied quadtree model. The associated data structures are studied and the algorithms are implemented. The experimental results indicate that the algorithms are efficient and can meet the current practical requirements on dynamic analysis and roaming of multiresolution terrain.(6) The 3D terrain visualization based on the virtual reality modeling (VRML) is discussed. In accordance with VRML syntax, the VRML's prototype nodes are designed. These overcome the difficulties in bringing huge terrain data into VRML world, high precision-computing, and real-time interactive roaming.