Research On Techniques For Multiresolution Representation And Visualization Of Large Scale 3D Digital Terrain

Three dimensional terrain models can always be important parts in virtual environments, and a wide range of demanding application fields exist. The dissertation focuses its research on the multiresolution representation, simplification and rendering of large-scale 3D terrain models. New methods and techniques are presented.At first, methods based on geometry analysis for multiresolution representation, simplification and rendering of terrain models are investigated. From the points of view of multiresolution schemes and simplification techniques, those known major algorithms are classified and summarized. A simplification algorithm for terrain models based on the normal vectors of mesh vertices is proposed. Its rule of simplification grounds on visual features, error metrics is from normal vectors of mesh vertices and simplifying technique is vertex removal. Based on the algorithm, a view-dependent simplification and rendering method for terrain models is developed. The method achieves view-dependent simplification by using virtual surrounding sphere of a mesh vertex for error measurements. Experiments have proved that the proposed methods are effective.In the portion of research on wavelet analysis based methods for multiresolution representation, simplification and rendering of terrain models, a three step approach to the choice of appropriate wavelet transform and the best wavelets according to application requirements is propsed: The first step chooses the type of wavelet transform, the second step determines candidate wavelets by picking out satisfying wavelet characteristics, and the last step selects the best wavelets from the candidates through wavelet parameterization. For lifted descrete wavelet transforms, an implementation method based on the Finite State Machine is provided and delayed normalization is suggested as an accelerating technique to improve transforming performance, setting up an uniform framework for implementing various lifted descrete wavelet transforms. After investigating an approach to terrain model simplification by using wavelet coefficients, an algorithm for large-scale terrain visualization is proposed. It first divides the big terrain model into blocks and performs wavelet transforms on them, then picks up visible blocks out from the model according the view, and finally simplify and render the terrain based on wavelet coefficients. The algorithm proves effective as it need neither static level of detail layers nor huge assistant data structures and is of low space complexity. Experiments confirm the effectiveness of methods for wavelets selection and algorithm for terrain simplification.The architecture of 3D terrain processing systems for network applications is also studied. A hybrid client-server structure for transmitting terrain images and models is suggested, and the scheme of corresponding transmission system is proposed. Thedesign and implementation of a hardware accelerated 3D electronic map system is described; capabilities, components and structure, implementation and runtime snapshots of the system are also covered.