一种适用于网络环境的三维网格压缩算法

为了使位流可以适应网络带宽的异构、时变以及各个网络终端的不同图形处理能力，提出了一种基于小波变换的三维网格分块渐进传输的压缩算法。利用细分曲面的模型表示方法，按照控制网格将几何体分块，采用嵌入式位平面编码方法对小波变换后每个小波子带的系数进行独立编码，生成多条独立的渐进压缩码流。该算法支持动态的质量可扩展性和分辨率可扩展性，能够从压缩结果中直接获得视点相关的模型表示。实验结果表明，该算法有利于提高多分辨率表示和传输效率，降低网络带宽需求。     

一种适用于网络环境的三维网格压缩算法

为了使位流可以适应网络带宽的异构、时变以及各个网络终端的不同图形处理能力,提出了一种基于小波变换的三维网格分块渐进传输的压缩算法。利用细分曲面的模型表示方法,按照控制网格将几何体分块,采用嵌入式位平面编码方法对小波变换后每个小波子带的系数进行独立编码,生成多条独立的渐进压缩码流。该算法支持动态的质量可扩展性和分辨率可扩展性,能够从压缩结果中直接获得视点相关的模型表示。实验结果表明,该算法有利于提高多分辨率表示和传输效率,降低网络带宽需求。     

基于渐进插值的Catmull-Clark双正交细分小波及其应用

针对lifting双正交Catmull-Clark细分小波在数据压缩、噪声滤波和低分辨率模型稳定性等方面的不足,提出基于渐进插值的Catmull-Clark双正交细分小波算法.对于任意拓扑的四边形网格,Catmull-Clark细分的极限曲面渐进插值于原有网格控制点,并且相邻2次细分之间网格改变程度很小,导致大量小波系数值趋于0,非常适于用零树编码提高3D网格的压缩性能;同时,该小波变换具有局部正交性和对位计算等特点,可显著减少内存占用量和计算复杂度.实验结果表明,与同类算法相比较,该算法在压缩效率、噪声滤波和低分辨率模型曲面的稳定性等方面均有明显提高,其中压缩编码Bits/vertex值减小14%,重构模型PSNR值增大5%,编解码耗时分别减少6%和9%.     

Loop细分小波框架对图形传输与去噪的应用

基于细分小波的多分辨率分析是近年来三维图形处理的重要方法,该方法在图形的压缩,去噪,渐近显示和传输,多分辨率绘制和编辑等领域已有很多研究与应用。最近Maria Charina等人提出了一种新的基于细分小波紧框架的多分辨率分析理论,使得细分小波框架在三维图形处理领域的应用成为值得研究的新课题。在深入学习和研究这种全新的多分辨率分析理论的基础上,详细推导了Loop细分小波紧框架的分解和重构公式,应用这些公式实现了多分辨率曲面的构造并将其应用到三维网格图形的渐进传输和去噪中。通过与M.Bertram的双正交Loop细分小波算法的对比,表明基于Loop细分小波紧框架的多分辨率分析算法具有较好的渐进传输和去噪效果。由于通常的输入网格不具有细分连通性,而基于细分曲面的多分辨率分析算法要求它所处理的网格具有这种连通性,所以还特别提出了一种构造既能逼近输入网格又具有细分连通性的网格的简捷算法。     

隐式曲面的多分辨率法向网格逼近

法向网格是一种新型的曲面多分辨率描述方式，其中每个层次都可以表示为其前一个粗糙层次的法向偏移．文中提出一种基于法向网格表示的隐式曲面多分辨率网格逼近算法．首先通过基于空间剖分技术的多边形化算法获得隐式曲面的粗糙逼近网格，并利用网格均衡化方法对粗糙网格进行优化，消除其中的狭长三角形；然后利用法向细分规则迭代地对网格中的三角面片进行细分，并利用区间算术技术沿法向方向对隐式曲面进行逼近．最终生成的隐式曲面分片线性逼近网格为法向网格．该逼近网格为隐式曲面提供了一种多分辨率表示，网格具有细分连通性，其数据量较传统的多边形化算法所生成的网格有大幅度的压缩．该算法可用于隐式曲面的多级绘制、累进传输及相关数字几何处理．     

基于小波变换的不规则网格的多分辨率分析

Lounsbery 提出了一种三角形网格多分辨率分析方法，但该方法只能应用于规则的三角形网格，且包含了重新网格化的过程。为了解决该问题，基于小波变换，该文扩展了Lounsbery的方法。该算法直接对不规则网格进行渐进压缩，得到了不同分辨率的网格。在此过程中还可以基于三角形网格的连接信息，对三角形网格进行优化，使之更加规则，从而使该文算法得到了改善。将该文算法与以前的算法进行了比较，结果表明，该文算法速度快，效果良好，有一定的实用性。     

一种基于误差控制的网格多分辨模型生成算法

提出一种网格多分辨模型生成算法．该算法以最大误差L∞控制的网格简化算法为基础，通过删除边和拆分点操作进行向下和向上采样，将网格模型表示为由一个低分辨率的网格和一系列修改操作组成的多分辨模型．同其它算法相比，该算法在初始向下采样时，重点考虑了简化误差对模型精度的影响．在生成网格多分辨模型时，该算法将细化操作分解为对网格模型的几何修改信息和各细化操作之间的关系信息，确保了多分辨模型的健壮性．该算法可通过三角片数和简化误差两种方法来调整网格模型分辨率，实验结果证明了本算法的有效性．     

多分辨率网格的数据压缩

在对三角形网格多分辨率分析中,为了避免重新网格化的过程,基于小波变换,扩展了Lounsbery的方法。该算法直接对不规则网格进行渐进压缩,得到了不同分辨率的网格。在此过程中还可以基于三角形网格的连接信息,对三角形网格进行优化,使之更加规则,从而使本文算法得到了改善。实验结果表明,算法速度快,效果良好,有一定的实用性。     

基于小波变换的非渐进网格压缩

为了取得较好的三角形网格压缩性能，提出了一种基于小波变换的三角形网格非渐进压缩方法。该压缩方法先利用重新网格化来去除大部分连接信息，然后利用小波变换的强去相关能力来压缩几何信息。在进行重新网格化和小波变换后，再按一个确定的次序将所有的小波系数扫描为一个序列，然后对其做量化和算术编码。另外，对重新网格化得到的自适应半正规采样模式，还设计了一种自适应细分信息编码算法，以便使解码端知道每一个小波系数应该放置在哪一个顶点上。实验表明，用该压缩方法对由三维扫描仪获取的复杂网格进行压缩，取得了比Edgebreaker方法明显要好的率失真性能；10比特量化时，压缩倍数在200倍左右，为Edgebreaker方法的2倍多。     

面向移动终端的三角网格逆细分压缩算法

针对移动用户的实时显示需求,提出一种基于逆细分的三角网格压缩算法.通过改进逆Butterfly简化算法,采用逆改版Loop模式,将细密的三角网格简化生成由稀疏的基网格和一系列偏移量组成的渐进网格;然后,通过设计偏移量小波树,将渐进网格进行嵌入式零树编码压缩.实验结果表明:该算法与以往方法相比,在获得较高压缩比的同时,运行速度较快.适用于几何模型的网络渐进传输和在移动终端上的3D图形实时渲染.     

A digital mock-up visualization system capable of processing giga-scale CAD models

In the automotive, aerospace and naval industries, digital mock-up tools are always used for assembly examination, layout examination and interference checking. Generally, a digital mock-up is assembled from giga-scale CAD models. Because of limitations of computer hardware resources, a digital mock-up represented by traditional planar facets is too large to load into a computer’s memory for rendering. This article proposes a new geometric compression representation to represent given CAD models with curved triangular patches. Based on the compression representation, our digital mock-up visualization system can import several giga-scale CAD models into a computer’s memory simultaneously. A high performance rendering strategy to display the curved triangular patches is also presented. In the rendering strategy, a dynamic subdivision algorithm is introduced which is different from conventional LOD techniques in order to reduce memory consumption. In addition, an algorithm to convert CAD models to the curved triangular patches is introduced.     

Reverse engineering with subdivision surfaces

Reverse engineering is concerned with the reconstruction of surfaces from three-dimensional point clouds originating from laser-scanned objects. We present an adaptive surface reconstruction method providing a hierarchy of quadrilateral meshes adapting surface topology when a mesh is refined. This way, a user can choose a model with proper resolution and topology from the hierarchy without having to run the algorithm multiple times with different parameters. The multiresolution mesh representation can be used subsequently for view-dependent rendering and wavelet compression.     

并行绘制系统Chromium中的3D模型数据压缩

网络带宽不足严重限制了Chromium等并行图形绘制系统渲染巨型几何场景的速度。通过对网络传输中的几何数据进行无损压缩,提出了一种能有效缓解网络负荷的方法。该方法可以很容易地实现不同算法对特定几何数据的压缩。实现了ZLib和哈夫曼算法对Chromium系统的压缩,测试了系统对10类OpenGL应用程序的加速比和压缩比,以及在4种配置环境下的并行运行效果。使用ZLib算法时,测试程序的运行速度都有不同程度的提高,最高提升3倍;数据压缩比平均在5.0以上,最高为30;并行绘制加速比在单服务器数目下最高。ZLib算法整体表现良好,能有效减少网络通信量。     

New multiresolution modeling techniques in CAD

To apply wavelet transformation to CAD surface model composed of multiple surface patches, an algorithm called wavelet signal separation to preserve geometric constraints during wavelet transformation is proposed. The algorithm divides the B-spline control points into those associated and those unassociated with the geometric constraints. Through preserving the signal information associated with the constraint control points, the geometric constraints can be automatically preserved after wavelet transformation. This paper also briefly investigates two types of the detail feature propagation technique in wavelet-based multiresolution CAD system. One is detail feature motion. The other is detail feature repetition. Finally, a comprehensive example is presented to illustrate the effects of the combination of those techniques.     

Compression of multiple depth maps for IBR

Image-based rendering techniques include those with geometry and those without. Geometric information in the form of a depth map aligned with the image holds a lot of promise for IBR due to the several methods available to capture it. It can improve the quality of generated views using a limited number of views. Compression of light fields or multiple images has attracted a lot of attention in the past. Compression of multiple depth maps of the same scene has not been explored much in the literature. We propose a method for compressing multiple depth maps in this paper using geometric proxy. Different quality of rendering and compression ratio can be achieved by varying different parameters. Experiments show the effectiveness of the compression technique on several model data.     

一种基于小波变换的分形零树混合编码方法

为了降低分形编码的复杂度和提高编码效率 ,提出了一种基于小波变换的分形零树混合图象编码方法 .该方法首先利用小波变换将图象分解为不同方向不同分辨率的子图象 ,然后分别在不同分辨率层将这些子图象以类似于零树的结构 ,构成一棵棵的小波子树 (wavelet subtree) ,最后在编码时 ,对每一棵小波子树进行具体的分析 ,或采用分形编码 (fractal coding) ,或采用零树编码 (zerotree coding) .与传统的基于小波变换的分形编码相比 ,此算法在充分利用子带图象间的相似性和块内存在的自相似性的同时 ,也充分利用了小波变换后子图象块内 ,特别是高分辨层的子图象块内所存在的大量局域性的冗余性 .实验结果表明 ,此方法在较大的压缩范围内 ,都能够获得较好的压缩效果 .     

Fast rendering of foveated volumes in wavelet-based representation

A foveated volume can be viewed as a blending of multiple regions, each with a different level of resolution. It can be efficiently represented in the wavelet domain by retaining a small number of wavelet coefficients. We exploit the arrangement of those wavelet coefficients to achieve fast volume rendering. The running time is O(n²+m), where n is the width of the rendered image, and m is the number of wavelet coefficients retained for the foveated volume. Our algorithm consists of two phases. The first phase is a fast reconstruction of the super-voxels from the wavelet coefficients, and the second phase renders the super-voxels by carefully tracking rays with different thickness in the super-voxels. No expensive preprocessing on the wavelet coefficients is required. Hence, it is possible to interactively modify different viewing parameters like the transfer functions. A potential application of our algorithm is in remote visualization of large volume data-sets.     

Autostereoscopic Rendering of Multiple Light Fields

Light fields were introduced a decade ago as a new high‐dimensional graphics rendering model. However, they have not been thoroughly used because their applications are very specific and their storage requirements are too high. Recently, spatial imaging devices have been related to light fields. These devices allow several users to see three‐dimensional (3D) images without using glasses or other intrusive elements. This paper presents a light‐field model that can be rendered in an autostereoscopic spatial device. The model is viewpoint‐independent and supports continuous multiresolution, foveal rendering, and integrating multiple light fields and geometric models in the same scene. We also show that it is possible to examine interactively a scene composed of several light fields and geometric models. Visibility is taken care of by the algorithm. Our goal is to apply our models to 3D TV and spatial imaging.