Comparative analysis of shape descriptors for 3D objects

Multimedia Tools and Applications - One of the basic characteristics of an object is its shape. Several research areas in mathematics and computer science have taken an interest in object...     

Structural shape prototypes for the automatic classification of 3D objects.

This technique for defining and constructing 3D shape prototypes improves automatic 3D content classification and search by summarizing key features of the members of a class, then classifying the query object into the class that the prototype most similar to the given query represents.     

Multi-mesh and adaptivity in 3D shape optimization

The major drawback in three-dimensional shape optimization is the excessive computational time needed in spite of the use of parametric-type design variables. Therefore, in addition to parametrization we suggest the use of several meshing levels to speed up the obtention of the optimal solution and to check the precision of the analysis by an error estimation. The combination of parametrization, multi-mesh and error estimation allows us to deal efficiently with three-dimensional shape optimization problems.     

Justification of a certain algorithm for shape optimization in 3D elasticity

The trabecular bone adapts its form to mechanical loads and is able to form structures that are both lightweight but very stiff. In this sense, it is a problem (for the Nature or living entities) similar to the structural optimization, especially the topology optimization. The structural optimization system developed by the authors previously was based directly on the bio-mechanical models. The paper aims to clarify the approach of using the bio-mechanical models of the trabecular bone remodelling phenomenon as a base for the structural optimization. The justified algorithm for shape optimization mimics the natural phenomenon to satisfy the condition of constant value of the strain energy density on the structural surface, issuing from the considerations in the area of mechanics. The main body of the paper contains the analysis of the stiffness optimization problem in the framework of speed method approach to shape optimization. The given numerical example (cantilever beam in bending) includes the influence of the structural surface curvature on the optimization procedure. The presented in the paper approach can be used as a method of structural optimization unrelated already to trabecular bone remodelling phenomenon.     

Watermarking 3D objects for verification

We introduce and investigate the fundamental similarities and differences of watermarking 3D graphic models compared to 2D images, and propose some solutions to address a class of applications of digital watermarking-the verification of 3D polygonal models. To our knowledge, watermarking of 3D objects for verification purposes has not been addressed in any published literature. The proposed scheme, in its present form, is not intended for use in applications that require robust watermarks. One recent work in 3D data hiding addressed applications requiring robust means of hiding data. We first introduce digital watermarking, discuss its goals and application domains, and explain the different categories of watermarks. We believe the goals and applications will remain fairly similar for 2D images and 3D models     

A three-dimensional shape optimization system—shop3D

A modular approach for shape optimization of three-dimensional solid structures is described. A major consideration in the development of this capability is the desire to use a commercially available finite element program, such as NASTRAN, for analysis. Since NASTRAN cannot be called as a subroutine, a system architecture was developed of independently executable modules in which sequential execution is controlled by job control language. Also, shape sensitivities are not commonly available in commercial programs. A hybrid approach which is based on the material derivative concept is developed to obtain shape sensitivities by post processing finite element results stored on files. A quick generation of a good optimization model combined with an efficient optimization system will result in a drastic design time saving. In this paper, different modeling approaches for shape optimization are discussed. Emphasis will be placed upon a special modeling technique which overlays the design model onto an already existing finite element model. Several automotive related examples are used to evaluate the program's effectiveness.     

再现3D对象

多亏有了Google上的一种免费工具,3D建模变得不再是一个痛苦而笨拙的过程。Jerome Turner介绍SketchUp的主要功能。     

基于最优最小生成树的三维模型形状优化方法

针对海量、异构、复杂的三维模型高效形状分析需求,提出基于最优最小生成树的三维模型形状优化方法。首先基于三维模型最小生成树（3D-MST）构造模型的结构描述;其次通过拓扑结构与几何形状检测并结合双边滤波与熵权值分布进行局部优化,获得模型的优化MST表示;最终基于优化的Laplacian谱特征,结合薄板样条函数（TPS）,实现模型的形状分析与相似性检测。实验结果表明,所提方法不仅有效地保留了模型的形状特征,而且可高效地实现复杂模型的稀疏优化表示,能进一步提高几何处理与形状检索的高效性和增强鲁棒性。     

Interactive optimization of 3D shape and 2D correspondence usingmultiple geometric constraints via POCS

The traditional approach of handling motion tracking and structure from motion (SFM) independently in successive steps exhibits inherent limitations in terms of achievable precision and incorporation of prior geometric constraints about the scene. This paper proposes a projections onto convex sets (POCS) framework for iterative refinement of the measurement matrix in the well-known factorization method to incorporate multiple geometric constraints about the scene, thereby improving the accuracy of both 2D feature point tracking and 3D structure estimates. Regularities in the scene, such as points on line and plane and parallel lines and planes, that can be interactively identified and marked at each POCS iteration, enforce rank and parallelism constraints on appropriately defined local measurement matrices, one for each constraint. The POCS framework allows for the integration of the information in each of these local measurement matrices into a single measurement matrix that is "closest" to the initial observed measurement matrix in Frobenius norm, which is then factored in the usual manner. Experimental results demonstrate that the proposed interactive POCS framework consistently improves both 2D correspondences and 3D shape/motion estimates and similar results cannot be achieved by enforcing these constraints as either post or preprocessing     

立体目标的宽基线图像匹配

为了匹配立体目标的图像特征,提出一种仿射不变的局部特征提取算法。根据高斯滤波器的形状和大小要与图像结构相适应的原理,该算法利用图像中的最大稳定极值区域(MSER)的协方差矩阵衡量局部图像结构,并将局部图像结构变换到圆形高斯滤波器适用的形式下,以解决视角和尺度变化问题。为了保证图像变换的正确性,采用旋转压缩的方式将各向异性的图像结构变换为各向同性的图像结构。最后在各向同性的图像结构上提取尺度不变特征变换(SIFT)特征点,并将SIFT特征点的坐标变回原图像坐标。实验结果表明该算法提取的局部特征是完全仿射不变的,在立体目标的宽基线图像匹配中表现出良好的效果。     

Representation and shape matching of 3-d objects

A three-dimensional scene analysis system for the shape matching of real world 3-D objects is presented. Various issues related to representation and modeling of 3-D objects are addressed. A new method for the approximation of 3-D objects by a set of planar faces is discussed. The major advantage of this method is that it is applicable to a complete object and not restricted to single range view which was the limitation of the previous work in 3-D scene analysis. The method is a sequential region growing algorithm. It is not applied to range images, but rather to a set of 3-D points. The 3-D model of an object is obtained by combining the object points from a sequence of range data images corresponding to various views of the object, applying the necessary transformations and then approximating the surface by polygons. A stochastic labeling technique is used to do the shape matching of 3-D objects. The technique matches the faces of an unknown view against the faces of the model. It explicitly maximizes a criterion function based on the ambiguity and inconsistency of classification. It is hierarchical and uses results obtained at low levels to speed up and improve the accuracy of results at higher levels. The objective here is to match the individual views of the object taken from any vantage point. Details of the algorithm are presented and the results are shown on several unknown views of a complicated automobile casting.     

面向2D对象形状识别的空间模糊查询研究

基于空间形状的查询与认知主体的空间推理密切相关。从空间认知的角度,通常希望查询结果是一类形状结构相似的对象集合。以形状的不确定性表达和模糊查询为研究内容,提出一种面向2D对象形状识别的空间查询方法--向心包络算法。算法将对象划分为以最大内径中心为公共点的三角形集合,在此基础上建立相应的形状度量方法,通过提取所有顶点关于对象整体结构的形状影响因子求得对象之间的形状相似度,并建立与模糊形状谓词的匹配关系。实验表明,该方法可以实现2D对象的空间模糊查询,且查询结果与模糊形状谓词基本一致。     

多模式3维视频形状编码

目的 具有立体感和高端真实感的3D视频正越来越受到学术界和产业界的关注和重视,未来在3D影视、机器视觉、远程医疗、军事航天等领域将有着广泛的应用前景。对象基3D视频是未来3D视频技术的重要发展趋势,其中高效形状编码是对象基3D视频应用中的关键问题。但现有形状编码方法主要针对图像和视频对象,面向3D视频的形状编码算法还很少。为此,基于对象基3D视频的应用需求,提出一种基于轮廓和链码表示的高效多模式3D视频形状编码方法。方法 对于给定的3D视频形状序列逐帧进行对象轮廓提取并预处理后,进行对象轮廓活动性分析,将形状图像分成帧内模式编码图像和帧间预测模式编码图像。对于帧内编码图像,基于轮廓内链码方向约束和线性特征进行高效编码。对于帧间编码图像,采用基于链码表示的轮廓基运动补偿预测、视差补偿预测、联合运动与视差补偿预测等多种模式进行编码,以充分利用视点内对象轮廓的帧间时域相关性和视点间对象轮廓的空域相关性,从而达到高效编码的目的。结果 实验仿真结果显示所提算法性能优于经典和现有的最新同类方法,压缩效率平均能提高9.3%到64.8%不等。结论 提出的多模式3D视频形状编码方法可以有效去除对象轮廓的帧间和视点间冗余,能够进行高效编码压缩,性能优于现有同类方法,可广泛应用于对象基编码、对象基检索、对象基内容分析与理解等。