【作者】 边前卫；

【导师】 何援军；

【作者基本信息】 上海交通大学 ， 计算机应用技术， 2011， 博士

【摘要】 随着工业设计、数字医疗、影视娱乐等计算机图形应用领域的发展,三维模型的数量已呈爆炸式增长趋势,研究一套高效的三维模型检索系统已是势在必行。文字检索直接根据关键字搜索,三维模型检索则可在检索窗口输入模型,再根据模型特征进行匹配搜索,因此,对三维模型检索的研究主要集中在查询接口(主要是检索模型的输入)和特征提取算法(主要是特征提取与匹配)。如何构建快速、符合人的交互感知且建模特征明显的模型查询接口是一个三维模型检索系统首先要解决的问题。查询接口的模型类型又与特征提取算法相关。用于查询接口的模型不同于传统的计算机图形学几何造型意义上的模型,但一般也分为表面模型和实体模型。实体模型因能够比较方便地提供体积信息而比表面模型在检索中的适用范围更广,而其中的体素实体模型则因其提供的体积信息的规则性而得到更多的重视。这也是为什么研究高性能的体素实体模型特征提取算法在三维模型检索领域成为研究热点的原因。在国家自然科学基金(60573146、61073086)的资助下,本文对体素实体模型的检索理论与应用进行了研究。研究的基本思路是基于交互手绘建模和基于图像建模,将两者生成的模型用于三维模型查询接口的模型输入,从中提取模型特征进行检索匹配,完成查询工作。本文的主要工作与贡献可总结为以下四方面:(1)提出了一个基于体素实体模型的三维模型检索框架。该检索框架围绕体素实体模型这个中心,以此模型的规则化三维体积信息的获取、输入并检索展开,由查询接口、体素实体模型库、特征提取算法和相似度比较及输出构成。据对国内外文献的检索,本文构建的三维模型检索框架首次将具有一定规模的体素实体模型系统地应用于三维模型的检索。(2)在交互手绘模型构建与查询接口方面,本文提出了一种基于虚拟绘图面的法向体素生成算法和一种基于种子邻接关系的体素实体编辑算法。基于虚拟绘图面的法向体素实体生成算法由法向等高生成算法和法向梯度生成算法两部分组成,基于种子邻接关系的体素实体编辑算法则由半封闭曲线编辑算法和封闭式曲线编辑算法构成。这套能够实时反馈的模型生成和编辑方法为模型查询提供了灵活的交互式的模型输入并查询的接口,可充分发挥人的直观认知。该模型查询接口还将手绘的二维信息映射为三维模型信息,直接构造具有空间拓扑结构和规则体素信息的体素实体模型,克服了只依靠二维信息提取模型特征时空间信息不足的缺陷。(3)提出了一种基于序列图像建模、可提供多种模型特征的模型查询接口。该模型查询接口建立在基于序列图像的三维重建方法之上,以堆叠物体截面形状方式生成物体模型:首先通过经典SIFT算法得到各视图和底面参考图像间的初级特征点匹配,接着用本文提出的一种改进的RANSAC算法过滤出更具全局意义的匹配点集,并由该点集计算底面和截面上的单应变换矩阵;再由本文提出的基于Lab色彩空间的轮廓提取算法得到的物体轮廓,经由单应变换得到在底面和各截平面上的交叠形状;最后,本文提出了一种基于二值网格的体素实体建模算法将交叠形状组装为体素实体模型。相对于一般的基于图像建模方法,本文采取的三维重建方法可以为模型检索提供更为多样的截面形状、体积、拓扑等模型特征。(4)提出了一种基于体素实体模型的特征提取算法。该算法从体素实体模型中提取出体素的空间分布函数,是一种在体积层面做信息统计的特征提取算法。通过该算法得到的旋转不变性特征描述符VD2能够提供同类模型的共性特征,也能提供差异化的类间特征。与经典D2、GD2等基于表面模型的特征描述符相比,VD2具有更高的检索性能。此外,为了也能从表面模型中提取VD2特征描述符,本文还提出了一种基于射线权值的表面模型体素化算法。该算法可以在单次扫描体素化的过程中完成包围空腔、表面孔洞等表面网格退化现象的修复。以上四个方面的研究是在基于体素实体模型的三维模型检索框架下进行的,涉及模型查询接口构建和模型特征提取两个不同层面的三维模型检索关键技术,并在基于规模化体素实体模型的三维模型检索原型系统中得到了验证。更多还原

【Abstract】 With the development of computer graphics application domains, such as industrial design, digital medical care and entertainment, the amout of 3D models experiences an explosive growth. As the text search emerged from information expansion of internet, a 3D model retrieval system with high-efficiency is highly expected. For the time being, research interests of 3D model retrieval focus on query interfaces and feature extraction algorithms.Compared with traditional text query interface, model query interface can provide intuitive 3D model information, especially in the condition lacking text description. How to construct a fast, perception adaptive model query interface, which can offer model feature with high distinction, is the key of query interface research.Model type provided by query interface is corresponding to feature extraction algorithm. 3D model type includes surface model and solid model. Compared with surface model, solid model can provide volume information with low cost. Voxel model, which is a sort of solid model, is attracting more research interests in 3D model retrieval due to its regular solid information.Under the funding of National Natural Science Foundation (60573146, 61073086), this dissertation is devoted to theoretic and application research on 3D model retrieval system based on voxel model. Through research of sketch modeling and image based modeling, both of these two aspects, which can establish voxel model, are introduced to model query interface in 3D model retrieval. The work and contribution of this research are as follows:1. Present a 3D model retrieval framework based on voxel model. The core processing element of this framework is voxel model information. In theoretic level, this framework includes acquisition and retrieval of 3D regular information provided by voxel model. In application level, this framework includes model query interface, voxel model database, feature extraction and comparision. From the search of papers, retrieval system consturcted under this framework is the first one to introduce certain scale voxel modeling to 3D model query interface.2. For sketch modeling query interface, a virtual canvas based normal voxel generation method and a seed adjacency based voxel modification method are prsented.The virtual canvas based normal voxel generation method consists of normal equal altitude algorithm and normal gradient algorithm. The seed adjacency based voxel modification method consists of half-closed curve algorithm and closed curve algorithm. This set of voxel generation method and voxel modification method with real-time feedback support the voxel model query interface. This voxel model query interface, which is from the intuitionistic visual cognition of human, maps 2D drawing information into 3D model information, neatly constructs topology structure and regular voxel information of voxel model, solves the lack of space information in pure 2D query interface. From experiments, this interactive query interface, based on its ease of use, can provide quick access to voxel model, which is adaptive for volume feature extraction.3. Present a 3D model query interface based on image modeling, which is based on images in sequence and does provide a wide range of model features.This query interface is constucted under the image modeling method based on images in sequence. Meanwhile, this image modeling method constucts 3D model in the way of stack of cross-section shapes. In detail, this modeling method firstly introduces classic SIFT algorithm to produce primary feature mathing between views and ground view. Then, through an advanced RANSAC algorithm presented by this dissertation, more resonable and global mathing pairs will be generated. From these matching pairs, the homography on ground and cross section will be caculated. The silhouettes of model in every view will be cut out by a silhouette extraction algorithm based on Lab color space. After that, these silhouettes will be transfomed by homographies and crossover each other to generate cross-section shapes of real model. Finally, a voxel modeling method based on binary grid is presented to build voxel model from these cross-section shapes. Compared with usual image based modeling method, this 3D reconstruction method can provide various model features as cross-section shapes, volume and topology. As the constructed result of this modeling method, voxel model, which is full of volume feature, can be used by model query interface. Experiments show that this model query interface is practical.4. A feature extraction algorithm based on voxel model is presented.This feature extraction algorithm,which is a statistical method on volume level, adds up the voxel distribution function from voxel model. From this algorithm, a rotation-invariant descriptor called VD2, which can simultaneously provide common features among models in the same class and differential features among models in different classes, is generated. Compared with classic D2 and GD2, which are feature descriptors based on surface model, VD2 has higher retrieval efficiency. In addition, for the VD2 extraction from surface model, a voxelization method based on radial weight is presented. This voxelization method can repair surface degeneration as cavums and holes in just one-step. Compared with traditional method, this voxelization method can provide voxel models with more robust volume information.All these four research aspects are correlative and independent. They are inplemented under the voxel based 3D model retrieval framework and do research on query interface and feature extraction. They work as an organic whole. Relative experiments show the practical value of the 3D model retrieval system.更多还原