基于整数中轴骨架的3维模型检索算法

针对3维模型检索算法性能较低的问题,提出了一种基于整数中轴骨架的3维模型检索算法。在对3维模型进行姿态调整和各向同向性预处理后,提取模型的整数中轴骨架,并记录每个骨架点相应的几何信息,对提取的骨架按不同的空间区域划分,形成模型骨架二叉树。为了能够描述骨架二叉树的不同节点对模型整体相似性匹配的影响程度,为每个节点定义一个特征权值,其大小由该节点对应的骨架区域大小所决定。最后,采用由粗到细逐步淘汰的策略计算不同模型的相似度。对一个标准3维模型测试数据库的检索实验结果表明,由于将模型的拓扑结构和统计特征相结合,该算法可以得到较好的检索性能。     

基于中轴变换的骨架特征提取算法

针对中轴变换算法提取骨架特征时,其结果对边界噪声敏感且易产生毛刺的问题,提出一种基于中轴变换的改进算法。采用Voronoi图计算原始中轴,使用改进的二次误差度量方法去除毛刺。在二维及三维数据集上的实验结果表明,该算法能够提取简洁、准确的骨架,且对边界噪声具有鲁棒性。     

实体模型的多分辨率中轴生成

针对模型降维的需要,提出一种实体模型的多分辨率中轴生成方法.首先根据模型的层次寻找模型中需要细化的部分,并据此对边界进行体素化;其次使用距离蔓延的方法计算多分辨率体素的距离;最后根据体素的距离计算出多分辨率的中轴体素.实验结果表明,该方法可以以低时间空间代价生成高质量的多分辨率中轴.     

三维模型骨架的矫正

对复杂的三维模型进行骨架提取时，目前用各种骨架提取方法得到的骨架均可能产生偏离中心位置和冗余分支的失误情况．为此，提出一种骨架矫正方法，以改正骨架中的这些质量问题．在基于距离场提取骨架后，该方法对骨架的各个关节点进行如下的考察：以关节点为中心，向四周均匀发出辐射线与模型边界相交得到辐射线段，统计这些线段长度的分布以探知该关节点是否位于中心位置．对于偏离中心位置的关节点,使它向中心位置偏移，并修改相应的骨架分支，从而实现骨架的自动矫正．实验表明，新方法能很好地矫正三维骨架，且矫正速度很快，一般不超过骨架抽取时间的2％．     

Matching 3-D Models to 2-D Images

We consider the problem of analytically characterizing the set of all 2-D images that a group of 3-D features may produce, and demonstrate that this is a useful thing to do. Our results apply for simple point features and point features with associated orientation vectors when we model projection as a 3-D to 2-D affine transformation. We show how to represent the set of images that a group of 3-D points produces with two lines (1-D subspaces), one in each of two orthogonal, high-dimensional spaces, where a single image group corresponds to one point in each space. The images of groups of oriented point features can be represented by a 2-D hyperbolic surface in a single high-dimensional space. The problem of matching an image to models is essentially reduced to the problem of matching a point to simple geometric structures. Moreover, we show that these are the simplest and lowest dimensional representations possible for these cases.We demonstrate the value of this way of approaching matching by applying our results to a variety of vision problems. In particular, we use this result to build a space-efficient indexing system that performs 3-D to 2-D matching by table lookup. This system is analytically built and accessed, accounts for the effects of sensing error, and is tested on real images. We also derive new results concerning the existence of invariants and non-accidental properties in this domain. Finally, we show that oriented points present unexpected difficulties: indexing requires fundamentally more space with oriented than with simple points, we must use more images in a motion sequence to determine the affine structure of oriented points, and the linear combinations result does not hold for oriented points.     

三维图形简化新算法

本文的图形简化新算法,具有保细节.保真和快速等优点D快速是采用传播法快速形成近平面块的结 果D保真和保细节都是可以控制的.算法规整,效果良好,适应面宽,很有实用价值.     

Topology Preserving Simplification of Medial Axes in 3D Models

We propose an efficient method for topology‐preserving simplification of medial axes of 3D models. Existing methods either cannot preserve the topology during medial axes simplification or have the problem of being geometrically inaccurate or computationally expensive. To tackle these issues, we restrict our topology‐checking to the areas around the topological holes to avoid unnecessary checks in other areas. Our algorithm can keep high precision even when the medial axis is simplified to be in very few vertices. Furthermore, we parallelize the medial axes simplification procedure to enhance the performance significantly. Experimental results show that our method can preserve the topology with highly efficient performance, much superior to the existing methods in terms of topology preservation, accuracy and performance.     

Transitions of the 3D Medial Axis under a One-Parameter Family of Deformations

The instabilities of the medial axis of a shape under deformations have long been recognized as a major obstacle to its use in recognition and other applications. These instabilities, or transitions, occur when the structure of the medial axis graph changes abruptly under deformations of shape. The recent classification of these transitions in 2D for the medial axis and for the shock graph was a key factor in the development of an object recognition system where the classified instabilities were utilized to represent deformation paths. The classification of generic transitions of the 3D medial axis could likewise potentially lead to a similar representation in 3D. In this paper, these transitions are classified by examining the order of contact of spheres with the surface, leading to an enumeration of possible transitions which are then examined on a case-by-case basis. Some cases are ruled out as never occurring in any family of deformations, while others are shown to be nongeneric in a one-parameter family of deformations. Finally, the remaining cases are shown to be viable by developing a specific example for each. Our work is inspired by that of Bogaevsky, who obtained the transitions as part of an investigation of viscosity solutions of Hamilton-Jacobi equations. Our contribution is to give a more down-to-earth approach, bringing this work to the attention of the computer vision community, and to provide explicit constructions for the various transitions using simple surfaces. We believe that the classification of these transitions is vital to the successful regularization of the medial axis in its use in real applications.     

Parallel Thinning Algorithms on 3D (18, 6) Binary Images

Thinning algorithms on binary images are used to generate skeletons that preserve the same connectivity structures as the objects in the original images. Two kinds of skeletons may be appropriate for 3D thinning algorithms: digital curves and digital surfaces. We propose two thinning algorithms on 3D (18, 6) binary images. One algorithm generates skeletons as digital curves and the other algorithm generates skeletons as digital surfaces. Both algorithms are 6-subiteration algorithms—in each iteration, they are applied alternatively to delete border voxels from each of the six directions, upper, lower, north, south, east, and west.     

基于表面及切向属性的点模型骨架提取方法

针对目前在离散点云模型以及低分辨率模型上提取骨架算法存在的局限性,提出一种基于表面及切向属性(attributesofsurfaceandtangency,AST)的新方法.首先给出两个属性定义及其计算方式.然后基于上述属性通过表面光滑收缩和骨架吸引的双重作用达到模型的几何收缩,连接迭代收缩完成后得到的中心点,从而得到模型的骨架.实验表明:该方法得到的骨架能较好地表达原始模型的几何特征和拓扑结构,在缺少连接信息和低分辨率的情况下也能获得较好的骨架提取效果.     

Automatic Reconstruction of Unstructured 3D Data: Combining a Medial Axis and Implicit Surfaces

This paper presents a new method that combines a medial axis and implicit surfaces in order to reconstruct a 3D solid from an unstructured set of points scattered on the object's surface. The representation produced is based on iso-surfaces generated by skeletons, and is a particularly compact way of defining a smooth free-form solid. The method is based on the minimisation of an energy representing a “distance” between the set of data points and the iso-surface, resembling previous reserach¹⁹. Initialisation, however, is more robust and efficient since there is computation of the medial axis of the set of points. Instead of subdividing existing skeletons in order to refine the object's surface, a new reconstruction algorithm progressively selects skeleton-points from the pre- computed medial axis using an heuristic principle based on a “local energy” criterion. This drastically speeds up the reconstruction process. Moreover, using the medial axis allows reconstruction of objects with complex topology and geometry, like objects that have holes and branches or that are composed of several connected components. This process is fully automatic. The method has been successfully applied to both synthetic and real data.     

A Description and Evaluation of Various 3-D Models

Overcoming the limitations of polygonal techniques, parametric representations of curved lines and surfaces have evolved into powerful tools for today's computer graphics modeling applications.     

Probabilistic Models of Appearance for 3-D Object Recognition

We describe how to model the appearance of a 3-D object using multiple views, learn such a model from training images, and use the model for object recognition. The model uses probability distributions to describe the range of possible variation in the object's appearance. These distributions are organized on two levels. Large variations are handled by partitioning training images into clusters corresponding to distinctly different views of the object. Within each cluster, smaller variations are represented by distributions characterizing uncertainty in the presence, position, and measurements of various discrete features of appearance. Many types of features are used, ranging in abstraction from edge segments to perceptual groupings and regions. A matching procedure uses the feature uncertainty information to guide the search for a match between model and image. Hypothesized feature pairings are used to estimate a viewpoint transformation taking account of feature uncertainty. These methods have been implemented in an object recognition system, OLIVER. Experiments show that OLIVER is capable of learning to recognize complex objects in cluttered images, while acquiring models that represent those objects using relatively few views.     

Surface tension powered self-assembly of 3-D micro-optomechanicalstructures

A new surface micromachining process for surface tension powered self-assembly of silicon-based microstructures is described. Mechanical parts are formed from bonded silicon-on-insulator material and rotated out-of-plane by melting photoresist pads at tow temperature. Simple mechanisms that allow accurate control of the final angle are introduced and used to construct fixed 45° mirrors and scanning mirror assemblies     

Approximation-Based Similarity Search for 3-D Surface Segments

The issue of finding similar 3-D surface segments arises in many recent applications of spatial database systems, such as molecular biology, medical imaging, CAD, and geographic information systems. Surface segments being similar in shape to a given query segment are to be retrieved from the database. The two main questions are how to define shape similarity and how to efficiently execute similarity search queries. We propose a new similarity model based on shape approximation by multi-parametric surface functions that are adaptable to specific application domains. We then define shape similarity of two 3-D surface segments in terms of their mutual approximation errors. Applying the multi-step query processing paradigm, we propose algorithms to efficiently support complex similarity search queries in large spatial databases. A new query type, called the ellipsoid query, is utilized in the filter step. Ellipsoid queries, being specified by quadratic forms, represent a general concept for similarity search. Our major contribution is the introduction of efficient algorithms to perform ellipsoid queries on multidimensional index structures. Experimental results on a large 3-D protein database containing 94,000 surface segments demonstrate the successful application and the high performance of our method.     

无对应点三维表面重建的全局优化算法

一、三维平面重建问题陈述图1是成象系统,包括一对焦距f=1的照相机。两坐标系间的关系是 (X_R,Y_R,Z_R)=(X_L-b,Y_L,Z_L)。三维点(X_L,Y_L,Z_L)在左、右图象平面的投影分别是 (x_L,y_L)=(X_L/Z_L,Y_L/Z_L) (x_R,y_R)=(X_R/Z_R,Y_R/Z_R) =((Z_L-b)/Z_L,Y_L/Z_L) (1)则水平和垂直方向的差异场分别是δ_x=x_L-x_R=b/Z_L; δ_y=y_L-y_R=0 (2) 图1 平行轴立体成象系统假设三维点位于平面Z=Z_0+PX+QY上,则对应点匹配约束条件是