三维复杂模型快速简化及交互方法的研究

【作者】 费广正；

【导师】 吴恩华；

【作者基本信息】 中国科学院软件研究所 ， 计算机应用技术， 2001， 博士

【摘要】 模型简化（Model Simplification）技术是目前计算机图形学的研究热点之一。它不仅 成功应用于各种虚拟现实系统中，而且对于科学计算可视化、真实感绘制、计算机视觉、 网络传输等也有着十分重要的作用。 本文对三维复杂模型的快速简化及交互技术进行了研究。为适应动态场景的需求，本 文首先对递进网格生成方法进行了改进，使之可实时地或在尽可能少的预处理时间内生成 模型的递进网格表示，接着以此为基础提出了一种基于递进网格的模型编辑新方法，最后， 针对目前模型复杂度进一步增大，以致无法一次装入内存中进行处理这一状况，本文给出 了一种基于细节迁移优化外存简化模型的方法。本文的主要贡献如下： 1．在递进网格生成中，以运算量很少的局部误差度量替代了先前耗时的全局误差度 量，同时对代价排序过程进行了优化设计，从而大大提高了算法效率，使得将递进网格生 成算法用于动态场景成为可能。 2．提出了一种基于递进网格的模型编辑新方法。在该方法中，首先提供了模型的多 个层次进行编辑，编辑时结合调和映射产生形变最小的原则，实现三维区域与二维区域的 映射，从而使编辑操作更加直观。算法还实现了将编辑结果向粗略和精细两个方向的平滑 传播，动态维护了模型各个层次间的一致性。 3．提出了一种基于细节迁移对外存简化模型进行优化的新方法。算法在对原模型聚 类生成的简化模型的同时进行统计分析，得出模型的细节分布状况，并依此对简化结果模型进行细节迁移，从而避免了传统模型简化方法对模型局部拓扑的依赖，算法在保持线性 处理速度以及仅与简化模型规模相当的空间需求下，大大改善了简化模型的质量。 4．给出了一个虚拟漫游系统—虚拟大三巴教堂的设计过程和结果。该系统中结合建 筑物身的结构特点，对教堂的交互漫游控制进行了约束，使用户产生更加真实的体验； 中科院软件所博士学位论文 摘 要！ 另外还使用了“Portal”技术加速对场景可见性的判定，提高了场景的绘制速度。I 本文共分七章，第一章对各种三维图形加速方法进行了讨论，指出了各自的特点。第D 二章总结了己有的模型简化方法，指出了算法中需要考虑的若干问题，并对国内外己有的I 模型简化算法进行了系统的分类。第三章提出了适应动态场景的递进网格实时生成算法。【 第四章给出了基于递进网格的模型编辑新方法。第五章给出了一种基于细节迁移优化外存D 简化模型的方法。第六章介绍了虚拟漫游系统一虚拟大三巴教堂的设计过程和结果。第七D 章对本文的工作做了总结，并指出了进一步工作的方向。更多还原

【Abstract】 The technique of model simplification is one of the hot topics of computer graphics. It hasshown its broad applications in various directions,such as virtual reality, visualization, realisticrendering, computer vision, and progressive hondssion, etc.In this paper, efficient simplification and interaction techniques of large model are discussed.First, a real-time (or little-preprocess-required ) progressive mesh generahng algorithm ispresented for some applications where the models are required to be modifiable. Then, a novelmodel editing method based on the fast progressive mesh generaing algorithm is proposed. hast,in order to deal with models that are too large to fit in main memory, we present a newsimplifying method based on detail shifting. The main contribuion of this paper includes:1. Presentation of a real-time generating algorithin of progressive mesh for dynamicenvironment. Local error measurement with very little computing cost is taken in stead of globalerror measurement to speed up the algorithm. At the same time, the process of collaPse costsorting is optimised as well.2. Presentation of a novel model editing approach based on progressive-mesh. By theapproach, multiple levels of detail of a model are given at one time. Designer then selects a levelas an active level and a closed region from this level as an editing area. A hannonic map isdefined to embed the editing area of the active level onio a 2D rectangle where interpolation ofeach component of the editing information is computed in the rectangle and is then mapped backto the editing area to give the editing result. The editing result at the achve level could also beautomatically propagated onto all the coarser and finer levels.3. Illustration of an efficient and high quality out-of core simplification algorithm. By theapproach, a uniform samPling to the large model is first performed with statistic informationrecorded simu1taneous1y. The detail distribution of the original model is then acquired based onsuch infOrmation. bot, detail shifting from one part to the other of the initially unifonnlysampled n1odel is performed to show the non-uniform detail distribution. The algorithm greatlyimproves the quality of the result model while the processing tdrie is still linear to the model sizeand the memory cost is also small.4. Implementation of a walking-through system, ViAnal St. Paul Church. The projectconsists of three parts: modeling, rendering and walking-through simulation. As fOr the rendering,portal method is used to accelerate visibility culling, and fOr the walking-through simulation, inorder to improve the sense of reality, the architechture of the building is considered to constrainuser’s movement.The thesis is divided into seven chapters. In the first chaPter, several acceleration algorithmsof 3D graphics including levelxifdet8il representation are discussed, where the perfonnancerequiremnt and the proSPech of level-of-detaiI algorithm are described as well. In the secondchaPter, some ekisting algorithms for model simPlification are sununarized and categorized. Areal-time generating algOrithm of progressive mesh fOr dynamic environmnt is investigated inChaPter 3. ChaPter 4 illustrates a novel aPproach for model editing based on pregressive mesh.Chapter 5 explains an efficient nd high quality out-ofcore simPlification method based on detailshifting. In ChaPter 6, the imPlementation of a walkingdriugh system, Vtwal St. Paul Churchis described in brief as an instance. Finally, conclusions are drawn in Chapter 7.更多还原