三维几何数据压缩研究进展

三维几何数据压缩是指对描述三维场景的模型数据进行压缩,以便于模型数据的存储和网络传输,在分布式虚拟现实,协同应用,多用户视频游戏,模型数据在计算机内部的存储和传输有着非常重要的意义。文中介绍了三维几何数据压缩方法,分面向单分辨率模型的压缩和面向多分辩率模型的在进行阐述,并讨论了当前最新的研究进展,分析了目前尚存在的问题和研究前景。     

面向MPEG-4的三维几何压缩

随着数字通信技术的发展 ,三维多边形网格模型已广泛应用于虚拟环境、电子购物、协作CAD、多用户视频游戏、科学可视化等图形系统。这些系统要求对场景中复杂三维模型进行高效压缩从而减少模型的存储空间和网络传输时间。文中回顾了三维几何压缩的研究进展 ,介绍了三维多边形网格模型在MPEG - 4中的编码以及已成为MPEG - 4部分标准的拓扑手术和累进森林剖分压缩方法 ,并分析了目前方法存在的不足以及研究前景。     

三角形条带网格模型几何压缩方法研究

三角形条带为三角形网格提供了一种紧凑的表示方法，使快速的绘制和传输三角形网格成为可能，因此对由三角形条带构成的网格压缩进行研究具有重要的意义．本文使用Triangle Fixer方法对三角形条带构成的三维模型拓扑信息进行了压缩，并采用3阶自适应算术编码进一步提高压缩率；同时结合量化、平行四边形顶点坐标预测以及算术编码来实现三角形网格几何信息的压缩，在几何模型质量基本没有损失的情况下，获得了很好的压缩性能．     

一种三维物体建模和编码压缩方法

真实物体的三维建模和编码压缩是虚拟现实研究的热点问题.针对三维扫描设备采集的物体表面深度图像数据,文中提出了一种两幅深度图像的自动配准方法,以及基于回路的自动全局配准算法,可以快速、自动地配准全部深度图像,构造出逼真的三维模型.三维模型数据量大,为满足网络条件下的应用需求,文中提出了一种三维网格模型压缩编/解码方法,可编码压缩几何、拓扑和属性数据,压缩比高,并且支持递进传输.研究成果已成功应用在数字博物馆中.     

一种基于压缩感知的二维几何信号压缩方法

本文给出的压缩方法属于谱压缩方法. 谱压缩方法是一种常用的二维轮廓线模型压缩方法. 文章从压缩感知的角度解释了谱压缩方法, 并提出了基于压缩感知的二维轮廓线模型压缩方法. 首先利用二维轮廓线模型 Laplace 算子的特征向量构造了一组基. 二维轮廓线模型的几何结构在这组基下可以被稀疏表达. 利用随机矩阵对二维轮廓线模型的几何结构抽样, 完成压缩. 恢复过程中, 通过最优化1-范数, 实现几何信号的恢复. 实验结果表明, 该方法压缩速度快, 比例高, 恢复效果好, 适合对大型数据以及远距离数据进行压缩.     

一种保留特征的网格简化和压缩递进传输方法

针对数字博物馆中三维藏品网络传输及传输过程中藏品特征保留的需要,提出了一种保留拓扑及纹理特征的网格简化方法,在三角形折叠简化算法的基础之上,通过引入边界三角形和色异三角形等概念,对误差矩阵的计算和误差控制方法进行了改进,保留了原始模型的几何边界和纹理属性等特征信息;并结合递进网格和压缩编码,构造了基于八叉树编码的递进网格文件,从而实现了基于网络的三维模型递进传输系统.     

领域为人机界面、多媒体技术、嵌入式开发

通过对渐近网格(PM)技术与多属性压缩渐近网格(MACPM)技术的探讨,提出了采用扩展二次误差测度表示简化网格与初始网格的几何特征与其它属性信息的匹配程度,同时利用线性插值方法简化压缩算法,以减少解压对开销,且保证三维数据有更好的显示效果.实验证明,该方法不仅对三维几何模型信息得到较好的保留,其颜色信息也得到了有效的保留,并且MACPM技术相对PM技术在网络传输上总体效率有所提高.     

基于VRML文件的二进制压缩编码技术研究

VRML已经成为互联网上传输三维模型的主要文件格式。对于复杂场景模型具有数据信息量大的特点,尽管传统的VRML文件已采用了某种形式的压缩处理,但其文件仍旧相对庞大。因此,文章提出针对VRML文件的二进制压缩编码技术,对这些数据进行压缩处理,使之大小适合在网络中传输,同时压缩后的数据信息不影响虚拟可视化的显示质量。     

支持随机浏览的渐进几何压缩

由于三维物体的自遮挡,浏览三维网格是一个典型的随机访问问题.如果在将网格压缩后,只传输与解码当前视点下可见区域的数据,就可以节约网络带宽和解码资源.目前的网格压缩方法基本上没有考虑随机访问.提出一种基于小波变换且支持随机访问的渐进几何压缩方法,基本思想是将网格表面分成很多块,对每块的细节信息独立进行编码,然后只传输当前视点下可见块的细节信息.代表细节信息的小波系数被组织成零树,设计了一种修正的SPIHT算法来对每棵小波零树独立进行压缩.实验结果表明,该方法取得了与PGC方法相当的压缩效率,但如果只传输可见区域的细节信息,该方法需要传输的数据量只是PGC方法的60%左右.     

基于三维几何视觉重要性的纹理图像选择压缩算法

不同于传统二维图像,映射到三维模型上的纹理图像隐式包含了三维几何视觉信息. 然而,目前已有的纹理图像压缩方法并未考虑此特性. 本文提出了一种与三维模型几何视觉特性相关的纹理图像选择压缩算法. 首先给出一种结合纹理图像的显著性及其纹理走样的视觉重要性图构建方法, 将纹理图像划分为具有不同优先级别区域.之后,利用提出的选择压缩方法对它们进行不同比例压缩. 实验结果表明当选择本压缩算法时,纹理化三维模型能够获取较好的视觉效果.     

Compressed progressive meshes

Most systems that support visual interaction with 3D models use shape representations based on triangle meshes. The size of these representations imposes limits on applications for which complex 3D models must be accessed remotely. Techniques for simplifying and compressing 3D models reduce the transmission time. Multiresolution formats provide quick access to a crude model and then refine it progressively. Unfortunately, compared to the best nonprogressive compression methods, previously proposed progressive refinement techniques impose a significant overhead when the full resolution model must be downloaded. The CPM (compressed progressive meshes) approach proposed here eliminates this overhead. It uses a new technique, which refines the topology of the mesh in batches, which each increase the number of vertices by up to 50 percent. Less than an amortized total of 4 bits per triangle encode where and how the topological refinements should be applied. We estimate the position of new vertices from the positions of their topological neighbors in the less refined mesh using a new estimator that leads to representations of vertex coordinates that are 50 percent more compact than previously reported progressive geometry compression techniques     

TIN generation and point-cloud compression for vehicle-based mobile mapping systems

The vehicle-based mobile mapping system (MMS) is effective for capturing dense 3D data of roads, roadside objects and buildings. Since discrete points are not convenient for many application systems, a triangulated irregular network (TIN) is often generated from point-clouds. However, TIN data require two or three times larger storage than point-clouds. If TIN models can be promptly generated while loading point-clouds, it would not be necessary to store huge TIN models on a hard disk. In this paper, we propose two efficient TIN generation methods according to types of laser scanners. One is the line-by-line TIN generation method, and the other is the GPS-time based method. These methods can quickly generate TIN models based on scan lines of laser scanners. In addition, we introduce a new compression method to reduce the loading time of point-clouds. Our compression method is also based on the scan lines of laser scanners. Since points captured by a MMS tend to be positioned on nearly straight lines, their data size can be significantly reduced by coding the second order differences.     

On advances in differential-geometric approaches for 2D and 3D shape analyses and activity recognition

In this paper we summarize recent advances in shape analysis and shape-based activity recognition problems with a focus on techniques that use tools from differential geometry and statistics. We start with general goals and challenges faced in shape analysis, followed by a summary of the basic ideas, strengths and limitations, and applications of different mathematical representations used in shape analyses of 2D and 3D objects. These representations include point sets, curves, surfaces, level sets, deformable templates, medial representations, and other feature-based methods. We discuss some common choices of Riemannian metrics and computational tools used for evaluating geodesic paths and geodesic distances for several of these shape representations. Then, we study the use of Riemannian frameworks in statistical modeling of variability within shape classes.Next, we turn to models and algorithms for activity analysis from various perspectives. We discuss how mathematical representations for human shape and its temporal evolutions in videos lead to analyses over certain special manifolds. We discuss the various choices of shape features, and parametric and non-parametric models for shape evolution, and how these choices lead to appropriate manifold-valued constraints. We discuss applications of these methods in gait-based biometrics, action recognition, and video summarization and indexing.For reader convenience, we also provide a short overview of the relevant tools from geometry and statistics on manifolds in the Appendix.     

Single-rate near lossless compression of animated geometry

Representing mesh geometry in local rather than the world coordinate systems is very useful in many 3D animation processing applications. One can investigate the representation of vertex locations relative to a local coordinate frame (LCF) in the compression of dynamic 3D meshes. Unlike the world coordinates, which scatter in a wide range and show non-linear behavior of the vertices, the local coordinates exhibit a large clustering behavior of the vertex over time. This property is very useful for exploiting a large coherence over the vertex trajectory and between neighboring vertices. In this paper, we discuss the use of the LCF in static and animated mesh encoding and we introduce a new connectivity-guided predictive scheme for single-rate compression for animated meshes. The proposed geometry encoding strategy is based on a region growing encoding order, and only the differences between original and predicted locations are encoded in a local coordinate system, which splits into two tangential and one normal components. The approach is simple, efficient, and well-suited for real time applications.     

图像的无损压缩研究

着重从编码原理、发展现状和国际标准三个方面论述了图像的无损压缩研究及其现状,描述了基于不同解相关模型的无损压缩算法的主要思想。同时,由于无损方法的低压缩比有时很难满足某些实际应用的要求,文中进一步阐述了近无损压缩的概念,阐明了近无损压缩方法：基于感兴趣区域、视觉无损以及信息无损的具体含义,并就无损压缩以及近无损压缩研究领域内所存在的一些问题和更深一步研究的方向进行了一些有益的探讨。     

Wavelet-based progressive compression scheme for triangle meshes: wavemesh

We propose a new lossy to lossless progressive compression scheme for triangular meshes, based on a wavelet multiresolution theory for irregular 3D meshes. Although remeshing techniques obtain better compression ratios for geometric compression, this approach can be very effective when one wants to keep the connectivity and geometry of the processed mesh completely unchanged. The simplification is based on the solving of an inverse problem. Optimization of both the connectivity and geometry of the processed mesh improves the approximation quality and the compression ratio of the scheme at each resolution level. We show why this algorithm provides an efficient means of compression for both connectivity and geometry of 3D meshes and it is illustrated by experimental results on various sets of reference meshes, where our algorithm performs better than previously published approaches for both lossless and progressive compression.     

Interactive deformable geometry maps

Haptics on 3D deformable models is a challenge because of the inevitable and expensive 3D deformation computation. In this paper, we propose a new technique that extends the conventional rigid geometry images approach proposed by Gu et al. [9]. Our approach not only flattens the geometry, but also helps to accomplish deformation in an effective and efficient manner. Our approach is suitable for haptics computing, as it performs the deformation on the geometry map itself thereby avoiding the expensive 3D deformation computation. We demonstrate construction of the deformable geometry map representation and its application utilizing practical methods for interactive surgery simulation and interactive textile simulation.