Three-dimensional Terrain Real-time Rendering Technology Research

The rendering of 3D terrain scene is playing a key role in many research fields such as virtual reality, geographic information system and simulation system, etc. The principal contents in this thesis are as follow:There are many object models in 3D terrain scene. These models can be constructed by 3DS MAX which can assist VRML in constructing the models. The technologies of the object models' constructions and interactions based on 3DS MAX and VRML are introduced.The double cycles of uniform rows and columns algorithm is researched. Using the indexed vertex array can improve the efficiency of the rendering. The methods of gaining the height fields from the remote sensing images supplied by the China and Brazil Earth Resource Satellite are described. The rendering of the region around the Huangguoshu Falls is preliminarily realized by using the technologies discussed above.The real-time terrain rendering of continuous levels of detail based on the local entropy is put forward where the local entropy factor is treated as a new split metric factor. Because of the local entropies' irregular values, the error proliferations are used in a recursive process from bottom to top which can eliminate the cracks between the nodes with different levels of detail. The experimental results show that local entropy factor is a better split metric factor to test terrain blocks' coarsenesses.The real-time optimally adapting meshes algorithm is analyzed. It recursively executes the terrain rendering using different levels of detail. The recursions increase the CPU's implement spending. The GeoMipmapping algorithm is introduced. The GeoMipmapping algorithm partitions the terrain into blocks and each block may have different level of detail. To eliminate the cracks, this algorithm changes the structures of the blocks with higher levels of detail. We put forward a new algorithm called the GeoMipmapping algorithm with the skirts. In this algorithm, we adopt the technologies such as the terrain partition of any size, the computation of the projected errors, filling the cracks with the skirts, culling the invisible blocks and the triangle strips of vertex array. Based on this algorithm, we research the large textures' partition technology. A framework is established to manage the texture partitions and the corresponding terrain blocks. We elementarily realize real-time rendering of the region around the Huangguoshu Falls.