Carving for topology simplification of polygonal meshes

The topological complexity of polygonal meshes has a large impact on the performance of various geometric processing algorithms, such as rendering and collision detection algorithms. Several approaches for simplifying topology have been discussed in the literature. These methods operate locally on models, which makes their effect on the topology hard to predict and analyze. Most existing methods tend to exhibit several disturbing artifacts, such as shrinking of the input and splitting of its components. We propose a novel top-down approach for topology simplification that avoids most problems that are common in existing methods. We start with a simple, genus-zero mesh that bounds the input and gradually introduce topologic features by a series of carving operations. This process yields a multiresolution stream of meshes with increasing topologic level of detail. We further present a carving algorithm that is based on constrained Delaunay tetrahedralization. The algorithm first constructs the tetrahedral mesh of the complement of the input with respect to its convex hull. It then proceeds to eliminate tetrahedra in a prioritized manner. We present quality results for two families of meshes that are difficult to simplify by all existing methods known to us: topologically complex meshes and highly clustered meshes.     

面向Java 3D的CAD模型简化与转换

三维图形仿真的一个重要工作就是建立三维模型,若使用已有的模型可以节省一定的时间.文中主要讨论了如何将复杂的CAD模型应用于Java3D建立的图形仿真系统中.首先,对已有的Pro/E模型进行简化,以VRML格式导出,有两种方式应用于Java3D中.一种是直接编辑Pro/E模型导出的VRML格式文件,组织模型之间的链接关系;另一种是将Pro/E模型导出的VRML格式文件导入到3DMax中组织链接关系,然后导出为单一文件.最后联合使用这两种方式将一个复杂的空间机器人模型导入到Java3D,提高了图形数据的重用性和开发的快速性,经实践验证效果理想.     

Perception-based model simplification for motion blur rendering

Motion blur effects are important to motion perception in visual arts, interactive games and animation applications. Usually, such motion blur rendering is quite time consuming, thus blocking the online/interactive use of the effects. Motivated by the human perception in relation to moving objects, this paper presents simplified geometric models that enable to speedup motion blur rendering, which has not been tracked in motion blur rendering specifically. We develop a novel algorithm to simplify models with motion-aware, to preserve the features whose characteristics are perceivable in motion. We deduce the formula to outline the level of detail simplification by the object moving velocity. Using our simplified models, methods for motion blur rendering can achieve the rendering quality as using the original models, and obtain the processing acceleration mostly. The experimental results have shown the effectiveness of our approach, more acceleration with the larger models or faster motion (e.g. for the dragon model with over a million facets, the motion-blur rendering via hierarchical stochastic rasterization is sped up by over 27 times).     

From rendering to tracking point-based 3D models

This paper adds to the abundant visual tracking literature with two main contributions. First, we illustrate the interest of using Graphic Processing Units (GPU) to support efficient implementations of computer vision algorithms, and secondly, we introduce the use of point-based 3D models as a shape prior for real-time 3D tracking with a monocular camera.     

User-assisted simplification method for triangle meshes preserving boundaries

This paper proposes a user-assisted mesh simplification method applied to CAD models converted to triangle meshes. This work offers the possibility of simplifying each subobject independently and at different levels of detail. This way, the user can simplify the whole model and then modify some parts, by simplifying more or by refining the desired subobjects. This can be performed while the total number of triangles in the simplified model is maintained. In this method any error metric based on an edge collapse operation can be used. Boundaries between subobjects are preserved and important attributes in the final aspect of simplified models, like normals and texture coordinates, are also considered.     

An efficient and low-error mesh simplification method based on torsion detection

To preserve the major characteristics of the simplified model, this study proposes the use of torsion detection to improve the quadric error metric of vertex-pair contraction, and retain the physical features of the models. Besides keeping the physical features of the models, the proposed method also decreases the preprocessing time cost associated with analysis. To verify the conclusion, this research not only presents the effects of simplification and compares them with the vertex-pair contraction, but also employs Metro detection and image comparison to verify the error measurements. The experimental results demonstrate that the proposed method improves the error rate and keeps the precision of the object features efficiently.     

An effective quad-dominant meshing method for unorganized point clouds

To perform quad meshing on raw point clouds, existing algorithms usually require a time-consuming parameterization or Voronoi space partition process. In this paper, we propose an effective method to generate quad-dominant meshes directly from unorganized point clouds. In the proposed method, we first apply Marinov’s curvature tensor optimization to the input point cloud to reduce the umbilical regions in order to obtain a smooth curvature tensor. We then propose an efficient marching scheme to extract the curvature lines with controllable density from the point cloud. Finally, we apply a specialized K-Dimension (KD) tree structure, which converts the nearest neighbor searching problem into a sorting problem, to efficiently estimate the intersections of curvature lines and recover the topology of the quad-dominant meshes. We have tested the proposed method on different point clouds. Our results show that the proposed method produces good quality meshes with high computational efficiency and low memory requirement.     

An adaptive steganographic algorithm for 3D polygonal models using vertex decimation

Most 3D steganographic algorithms emphasize high data capacity, low distortion, and correct data extraction. However, their disadvantage is in the existence of the same embedding capacity for each data-embedded vertex in the 3D models. Embedding the same capacity in the vertex located on the surface with different properties may cause obvious distortion, making it difficult to achieve the initial goal of information-hiding techniques. This study proposes a new and adaptive 3D steganographic algorithm that considers the surface complexity. To increase the accuracy of the complexity estimation for each embedding vertex, the proposed algorithm adopts a vertex decimation process to determine its referencing neighbors. Thereafter, different amounts of the secret messages are embedded according to the surface properties of each vertex. This approach preserves important shape features and produces a more imperceptible result. Experimental results show that the proposed adaptive algorithm can achieve more accurate estimation results with a higher data capacity and acceptable distortion. The proposed technique is feasible in 3D steganography.     

An adaptive method for smooth surface approximation to scattered 3D points

The construction of a surface from arbitrarily scattered data is an important problem in many applications. When there are a large number of data points, the surface representations generated by interpolation methods may be inefficient in both storage and computational requirements. This paper describes an adaptive method for smooth surface approximation from scattered 3D points. The approximating surface is represented by a piecewise cubic triangular Bézier surface possessing C¹ continuity. The method begins with a rough surface interpolating only boundary points and, in the successive steps, refines it by adding the maximum error point at a time among the remaining internal points until the desired approximation accuracy is reached. Our method is simple in concept and efficient in computational time, yet realizes efficient data reduction. Some experimental results are given to show that surface representations constructed by our method are compact and faithful to the original data points.     

An unequal error protection method for progressively transmitted 3D models

In this paper, we present a packet-loss resilient system for the transmission of progressively compressed three-dimensional (3D) models. It is based on a joint source and channel coding approach that trades off geometry precision for increased error resiliency to optimize the decoded model quality on the client side. We derive a theoretical framework for the overall system by which the channel packet loss behavior and the channel bandwidth can be directly related to the decoded model quality at the receiver. First, the 3D model is progressively compressed into a base mesh and a number of refinement layers. Then, we assign optimal forward error correction code rates to protect these layers according to their importance to the decoded model quality. Experimental results show that with the proposed unequal error protection approach, the decoded model quality degrades more gracefully (compared to either no error protection or equal error protection methods) as the packet-loss rate increases.     

An adaptive normal estimation method for scanned point clouds with sharp features

Normal estimation is an essential task for scanned point clouds in various CAD/CAM applications. Many existing methods are unable to reliably estimate normals for points around sharp features since the neighborhood employed for the normal estimation would enclose points belonging to different surface patches across the sharp feature. To address this challenging issue, a robust normal estimation method is developed in order to effectively establish a proper neighborhood for each point in the scanned point cloud. In particular, for a point near sharp features, an anisotropic neighborhood is formed to only enclose neighboring points located on the same surface patch as the point. Neighboring points on the other surface patches are discarded. The developed method has been demonstrated to be robust towards noise and outliers in the scanned point cloud and capable of dealing with sparse point clouds. Some parameters are involved in the developed method. An automatic procedure is devised to adaptively evaluate the values of these parameters according to the varying local geometry. Numerous case studies using both synthetic and measured point cloud data have been carried out to compare the reliability and robustness of the proposed method against various existing methods.     

Line and point cluster models for spatial health data

Spatial cluster modelling of small area disease incidence and mortality has previously focused on clusters where excess risk is distributed around fixed points, and the aim is the reconstruction of these points (cluster centers). Often there is a need to assess clusters of a different form, such as around roads or river systems. These clusters are often linear or can be approximated by combinations of several linear segments. In this paper the recovery of point and line clusters is considered jointly. An example application is given where both linear or point clustering could be present.     

Advances in 3D data acquisition and processing for industrial applications

A critical task of vision-based manufacturing applications is to generate a virtual representation of a physical object from a dataset of point clouds. Its success relies on reliable algorithms and tools. Many effective technologies have been developed to solve various problems involved in data acquisition and processing. Some articles are available on evaluating and reviewing these technologies and underlying methodologies. However, for most practitioners who lack a strong background on mathematics and computer science, it is hard to understand theoretical fundamentals of the methodologies. In this paper, we intend to survey and evaluate recent advances in data acquisition and progressing, and provide an overview from a manufacturing perspective. Some potential manufacturing applications have been introduced, the technical gaps between the practical requirements and existing technologies discussed, and research opportunities identified.     

带纹理的三维模型简化算法

三维物体的几何造型中,物体通常用三角形网格来描述.随着计算机建模、仿真,虚拟现实与可视化技术的发展,经常会遇到带有纹理的三角形网格模型的简化问题.为此,提出一种带纹理的三角形网格模型简化算法.该算法中综合考虑了模型几何信息以及纹理信息的全局误差,并通过记录每步边折叠操作来消除累计误差,最终生成在形状和纹理上与原始模型最相似的简化模型.     

基于Creator的三维模型的简化研究

三维模型是虚拟现实系统中重要的组成部分,在三维模型的处理中存在两个主要问题：一是载入场景文件要花费很多时间;二是即使是在高性能的PC机上,浏览场景也是一件繁重而费时的事。当鼠标移动之后,场景变换要滞后几秒钟甚至几分钟。为此需要对模型进行优化,该文从简化模型和提高渲染速度两个方面介绍了基于Creator的优化三维模型及减少载入时间的几种方法。     

An adaptive framework for 3D graphics over networks

Access to and transmission of 3D models over networks becomes increasingly popular. However, the performance and quality of access to remote 3D models strongly depends on system load conditions and the capabilities of the various system components, such as clients, servers, and interconnect. The network graphics framework (NGF) integrates various transmission methods for downloading 3D models in a client–server environment. The NGF automatically selects the optimal transmission method for a given pair of client and server, taking into account characteristics of the model to be transmitted, critical environment conditions, user preferences and the capabilities of the client and the server. The NGF aims to provide constant quality of service across different clients and under varying environment conditions.     

An adaptive steganographic algorithm for 3D polygonal meshes

This paper presents a new adaptive digital steganographic technique for three-dimensional (3D) polygonal meshes. It is based on an adaptive substitutive blind procedure in the spatial domain. We use angle features to remove all restrictions of fixed embedding size in each vertex to provide larger embedding capacity and to minimize the distortion by minimum distortion distance estimation. This method exploits the correlation between neighboring polygons with respect to the human visual system to estimate the degree of smoothness or roughness properties. If the vertex is located on a rough surface, then it may tolerate larger position changes by embedding more messages than those on smooth surfaces. Our method provides an easy way to produce a more imperceptible result. In addition, a simple contagious diffusion technique is devoted to improving performance for polygonal meshes traversal. Experimental results show that the proposed technique is adaptive, simple, efficient, general, and secure. This technique has high capacity and low distortion, and it is robust against affine transformations. Our technique provides an adaptive method and has proven feasible in steganography.     

An approximate and efficient method for optimal rotation alignment of 3D models

In many shape analysis applications, the ability to find the best rotation that aligns two models is an essential first step in the analysis process. In the past, methods for model alignment have either used normalization techniques, such as PCA alignment, or have performed an exhaustive search over the space of rotation to find the best optimal alignment. While normalization techniques have the advantage of efficiency, providing a quick method for registering two shapes, they are often imprecise and can give rise to poor alignments. Conversely, exhaustive search is guaranteed to provide the correct answer, but, even using efficient signal processing techniques, this type of approach can be prohibitively slow. In this paper, we present a new method for aligning two 3D shapes. We show that the method is markedly faster than existing approaches based on efficient signal processing and we provide registration results demonstrating that the alignments obtained using our method have a high degree of precision and are markedly better than those obtained using normalization.