3D Visualization Research Of Large-area River Valley

The 3D terrain and river water are the main contents of the virtual valley environments, whose visualization has extensive application in the integrated management of valley digitalization and hydro information. The paper discussed and made research of the related technology such as multi-resolution presentation, simplication and realtime rendering of 3D valley terrain, large-scale rive water simulation and broadcast of massive terrain dataset over network, new methods and technology were introduced and presented.As for the visualization research of virtual valley system, the fundamental valley terrain data is an important component. The triangles numbers usually exceed the renering ability of the current graphics processor due to the DEM data amount of the large-area valley region. A method for real-time rendering of large-area terrain data was presented in this paper, which utilizes techniques such as terrain data block partition based on space filling curves, continuous level of detail (LOD), block-based view frustum culling and improved real-time optimal adaptive meshes (ROAM) algorithm. The whole terrain model of valley region was partitioned into equal size blocks and the blocks were arranged with space filling curves in multi resolution form. Fast clipping was achieved through block-based view frustum projection culling, high performance rendering was obtained through the improved four-queue ROAM algorithm which utilized the coherences between frames, and the data scale independent continuous LOD rendering was realized through data block partition and dynamic random access memory (RAM) managements. Experiments showed that our method is very efficient.The real-time modeling and rendering of large-scale dynamic river motion phenomenon is one of the most challenge problems in the research field of simulation, the river water is also the most important component in the virtual valley enviroment, and the simulation should realistically represent its dynamic behavior. The river water appered to be changed much at different region, there are no one modeling method can fits all the needs,This paper embraces a number of techniques covering all the steps of water motion simulation and focuses on the dynamic river surface generation and animation, we describes a combination of modeling methods for river water simulation: Perlin noise and FFT-based (Fast Fourier Transform) large-scale water surface modeling and dynamic flood peak generation on water surface using a physically based approach. Perlin noise based random wave fit for widen river surface and FFT-based wave can generate directional effect of flowing river, a linear compose was used to coupling the two and make a gradually change effect between different regions of the river. As for the dynamic flood peak phenomenon of flood routing process, we use a simple physical-based animated wave model similar to the gerstner wave model, flood peak models for different condition were generated beforehand, the animated model was loaded at runtime to move along the riverbed track, the moving speed can be changed dynamically, and it was mixed with the river surface model adaptively. The real-time rendering techniques for the large-scale 3D scene rendering such as LOD and seamless tiling of LOD water surface patches were discussed in detail, we have adapted them to the rendering of flowing river, a template culling method for fast clipping were also developed. The methods allow the user to interactively fly over a virtual valley, and there are presented results of implementation of the 3D visualization for river flood routing simulation.It is also important for the analysis result of hydrology and hydrodynamic information to be visiualized and queried over network, which made it necessary to construct a remote rendering platform for the large-area valley terrain data. A novel approach of wavelet-based progressive terrain data compression and streaming transmission method was thus proposed in this paper, which introduced a massive 3D terrain remote visualization solution over network. The large-area terrain models were partitioned into blocks, a lifting scheme wavelet was used for the datasets decorrelation, the mesh refinement and coarseing process was recast to the wavelet lifting and update framework, the and improved SPIHT algorithm was used for zero-tree wavelet encoding, the datasets was organized as progressive bitstream after compression, and the resolution of each visible terrain block was choosed adaptively according to the viewpoint and network bandwidth during interactive rendering.The framework of 3D terrain visualization and river water simulation systems for network applications is also studied. A hybrid client-server and browser-server architecture for transmiting terrain models and corresponding rendering solution were proposed, the design and implementation of a lare-area virtual valley simulation and visualization system was introduced in detail, the function, system framework, implementation and runtime snapshots of the system are also covered.