Research On An Adaptive Deformation Framework With Feature-preserving For Interactive Virtual Environment

As a 3D interactive technique, interactive deformation changes the 3D model surface to form diversified objects. Some of the existing deformation techniques create deformation systems beforehand to satisfy real-time process, yet without guaranteeing desirable results after a sequence of deformations;meanwhile, some construct the deformation system in real-time for optimal deformed results, but cannot support interactive operations. Composed by a pre-process and a real-time process, a general and efficient adaptive deformation framework is proposed in this thesis for providing an optimal deformation scheme for different applications.The pre-process creates a reasonable and dynamic scene structure, which is the basis for real-time deformation and rendering. A scene tree is built to describe all the 3D objects in the virtual scene;an active vertex tree is constructed for every complicated 3D model. The nodes of the global scene tree are catergorized into dummy nodes for scene management and shape nodes to represent model attributes. The separation of scene layout and model attributes enhances the flexibility of the tree structure and compresses the data volume.The dynamic progressive mesh hierarchy is based on Quadric Error Metric and Half Edge Collapse. To obtain an optimal half edge collapse sequence, extra processes on discontinuous appearance attributes and deformation related attributes are embedded into the hierarchy construction. The discontinuity problem of appearance attributes is solved based on diversity of relationships of vertex and seam. Appropriate penalties are added to the quadric error of certain collapsing operations to make mesh aberrances happen as late as possible. The problem of deformation-sensitive attributes is solved by analyzing the potential distortion on the geometric properties. Appropriate penalties are added to the modified quadric error to postpone the deformation distortion.The real-time process executes the real-time deformation, dividing into dynamic data preparation and dynamic deformation. Data preparation, consisting of dynamic evaluation and dynamic modification, designs reasonable model structure for deformation, where the evaluation specifies the levels of detail and mesh regularity and the modification changes the topological and geometric mesh structure. For deformation, four deformation primitives are proposed to normalize deformation constraints and linearize them for Laplacian operator.The deformation framework has been applied on general models to prove the performance. Furthermore, the framework is embedded into a virtual reality application-Virtual Museum Presentation and Navigation System to guarantee the realtime deformation with desirable visual quality.