【作者】 卢威；

【导师】 潘金贵；

【作者基本信息】 南京大学 ， 计算机应用技术， 2010， 博士

【摘要】 交互式变形技术是一种高级的三维交互技术,通过改变三维模型曲面得到多样化的物体模型。现有的变形技术或者预先创建变形系统以满足实时交互过程,但是不能保证在一系列变形之后依旧得到理想的变形结果；或者实时构建变形系统以确保最优的变形结果,但是不能保证实时交互操作。为了从整体上对交互式变形技术进行改进,本文从预处理和实时处理两个层面创建一个通用且高效的自适应变形框架,为不同的应用场合提供合理的变形处理方案。预处理阶段的主要任务是创建一个合理的动态的场景结构,作为实时变形和渲染的数据基础。本文用树型结构描述虚拟环境中三维对象之间的关系,并针对复杂三维对象构建由活动顶点树表示。全局虚拟场景树的顶点分为两类：一是抽象的哑元节点；另一类是表达模型属性的造型节点。这种将场景中对象关系与对象属性分离的实现方式,加强了场景树结构的灵活性且压缩了数据量。在构建复杂对象的层次式累进网格时,本文基于二次误差测度和半边折叠算子实现,加入了顶点外观属性和变形相关属性的特殊处理,优化半边折叠序列。对于非连续外观属性,本文分析顶点和接缝之间的各种关系,在原始二次误差的基础上给涉及外观接缝的半边折叠操作加上适当惩罚量,使得外观畸变在简化过程中尽可能地推迟；对于变形敏感属性,本文分析模型的几何属性在变形过程中可能出现的畸变,为每个半边折叠操作加上适当的惩罚量,使得变形可能造成的畸变尽可能地推迟。实时处理的主要任务是执行实时变形,分为动态数据准备和动态变形两个部分。动态数据准备通过动态评估和动态调整,为变形操作构建合理的数据信息。动态变形执行由用户控制的变形过程,针对动态变化模型,本文提出了四种变形约束基元对变形约束进行统一化处理,并设计了约束基元的线性化处理过程,将其嵌入到线性拉普拉斯算子中。由于半边折叠和边交换操作会改变网格模型的拓扑结构,本文定义线性拉普拉斯矩阵的动态调整规则,得到了一个完整的可随动态模型变化进行自适应调整的交互式变形系统。本文不仅对通用模型进行实验论证,还实现了一个虚拟现实应用——虚拟博物馆展示及漫游系统,取得了良好的效果。更多还原

【Abstract】 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.更多还原