Automatic Surface Reconstruction from Point Sets in Space

In this paper an algorithm is proposed that takes as input a generic set of unorganized points, sampled on a real object, and returns a closed interpolating surface. Specifically, this method generates a closed 2-manifold surface made of triangular faces, without limitations on the shape or genus of the original solid. The reconstruction method is based on generation of the Delaunay tetrahedralization of the point set, followed by a sculpturing process constrained to particular criteria. The main applications of this tool are in medical analysis and in reverse engineering areas. It is possible, for example, to reconstruct anatomical parts starting from surveys based on TACs or magnetic resonance.     

An Interactive Approach to Point Cloud Triangulation

We present an interactive system for the generation of high quality triangle meshes that allows us to handle hybrid geometry (point clouds, polygons,. . .) as input data. In order to be able to robustly process huge data sets, we exploit graphics hardware features like the raster manager and the z-buffer for specific sub-tasks in the overall procedure. By this we significantly accelerate the stitching of mesh patches and obtain an algorithm for sub-sampling the data points in linear time. The target resolution and the triangle alignment in sub-regions of the resulting mesh can be controlled by adjusting the screen resolution and viewing transformation. An intuitive user interface provides a flexible tool for application dependent optimization of the mesh.     

Generating Consistent Motion Transition via Decoupled Framespace Interpolation

The framespace interpolation algorithm abstracts motion sequences as 1D signals, and interpolates between them to create higher dimension signals, with weights drawn from a user specified curve in a bounded region. We reformulate the algorithm to achieve motion-state based transition via dynamic warping of framespaces and automatic transition timing via framespace frequency interpolation. Basis motions displaying diverse coordination configurations between upper and lower body-halves, cannot be consistently corresponded at a macro level. We address this problem here, through decoupled blending of these halves to achieve true consistency , and eliminate accumulated phase differences via cosine phase warp functions. This generalization enables interpolation of motions with diverse coordinations between the upper and lower bodies.     

Efficient Algorithms for Computing Conservative Portal Visibility Information

The number of polygons in realistic architectural models is many more than can be rendered at interactive frame rates. Typically, however, due to occlusion by opaque surfaces (e.g., walls), only small fractions of such models are visible from most viewpoints. This fact is used in many popular methods for preprocessing visibility information which assume a scene model subdivided into convex cells connected through convex portals. These methods need to establish which cells or parts thereof are visible to a generalized observer located within each cell. The geometry of this information is termed a 'visibility volume' and its computation is usually quite complex. Conservative approximations of viewing volumes, however, are simpler and less expensive to compute. In this paper we present techniques and algorithms which permit the computation of conservative viewing volumes incrementally. In particular, we describe an algorithm for computing the viewing volumes for a given cell through a sequence of ' m ' portals containing a total of ' n ' edges in O m n time.     

Integrating Occlusion Culling and Levels of Detail through Hardly-Visible Sets

Occlusion culling and level-of-detail rendering have become two powerful tools for accelerating the handling of very large models in real-time visualization applications. We present a framework that combines both techniques to improve rendering times. Classical occlusion culling algorithms compute potentially visible sets (PVS), which are supersets of the sets of visible polygons. The novelty of our approach is to estimate the degree of visibility of each object of the PVS using synthesized coarse occluders. This allows to arrange the objects of each PVS into several Hardly-Visible Sets (HVS) with similar occlusion degree. According to image accuracy and frame rate requirements, HVS provide a way to avoid sending to the graphics pipeline those objects whose pixel contribution is low due to partial occlusion. The image error can be bounded by the user at navigation time. On the other hand, as HVS offer a tighter estimation of the pixel contribution for each scene object, it can be used for a more convenient selection of the level-of-detail at which objects are rendered. In this paper, we describe the new framework technique, provide details of its implementation using a visibility octree as the chosen occlusion culling data structure and show some experimental results on the image quality.     

Directional Discretized Occluders for Accelerated Occlusion Culling

We present a technique for accelerating the rendering of high depth-complexity scenes. In a preprocessing stage, we approximate the input model with a hierarchical data structure and compute simple view-dependent polygonal occluders to replace the complex input geometry in subsequent visibility queries. When the user is inspecting and visualizing the input model, the computed occluders are used to avoid rendering geometry which cannot be seen. Our method has several advantages which allow it to perform conservative visibility queries efficiently and it does not require any special graphics hardware. The preprocessing step of our approach can also be used within the framework of other visibility culling methods which need to pre-select or pre-render occluders. In this paper, we describe our technique and its implementation in detail, and provide experimental evidence of its performance. In addition, we briefly discuss possible extensions of our algorithm.     

约束四面体剖分和三维物体表面重建

该文提出了约束曲面和约束最大空球凸多面体的概念,在此基础上设计了一种在空间区域上做约束Delaunay四面体剖分的算法。该算法的基本思路是首先对空间区域进行约束最大空球凸多面体剖分,然后在各个约束最大空球凸多面体内部做Delaunay四面体剖分。利用约束Delaunay四面体剖分算法,该文进一步设计了一种三维物体表面重建算法。     

基于映射法和Delaunay方法的曲面三角网格划分算法

提出一种曲面三角网格划分算法，该算法在曲面参数域中生成Delaunay类型的网格，然后将其映射到空间曲面，为了抵消映射过程中变形的影响，采用空椭圆准则代替传统的空间准则，并给出椭圆的构造算法以及椭圆圆心的定位方法，这些方法充分考虑到映射变形和求解速度，实验结果表明，该算法生成满意的曲面网格，具有一定的应用价值。     

基于光学三角几何关系的三维表面重建方法

工业图像处理作为图像处理技术的工业应用,是自动化技术的发展方向之一.传统的二维图像处理已经在视觉检测系统中广泛应用.目前利用光学方法的三维数字化具有越来越重要的意义.在工业生产中,多种获取三维数据的途径得到应用.其中最重要的方法有立体视觉,条形光相位平移法和条形光格雷编码法.本文重点介绍这三种方法在视觉检测系统中的运用.所开发的系统实现了被测工件可视化,而且更容易地将三维图像集成到生产线中.     

混合有理Bézier曲面及其三维重建

文章将Bernstein基函数与有理Bernstein基函数相结合,构造了一类新型有理曲面-混合有理Bézier曲面;给出了该类曲面的生成方法并讨论了曲面的性质。另一方面,在一种基于Newton-Thiele型非线性方法的插值曲面的三维重建理论基础上,讨论了由离散点集重建混合有理Bézier曲面的问题,为图形图象处理等研究领域提供了新的算法理论。     

基于Delaunay三角剖分和高斯小波函数插值的三维表面重建算法

在稀疏数据的三维表面重建中,通过插值的方法得到更为稠密的数据点是一个很重要的环节。该文在比较其它插值算法的基础上,提出了一种三维表面重建算法。该算法在对原始数据进行Delaunay三角剖分的基础上采用二维高斯小波函数插值,它不仅能有效地处理非均匀采样的三维稀疏数据,而且能克服其它插值算法中需要定义权重或估计参数的缺点。最终的实验结果验证了该算法的有效性和实用性。     

基于2维流形的STL曲面网格重建算法

STL（stereo lithography）作为3D扫描数据和快速原型制造事实上的标准,其广泛应用于娱乐、制造业和Internet等领域.但随着3D模型越来越复杂,数据量越来越庞大,从STL文件难以快速获得完整拓扑关系以及其存在大量冗余信息的缺点,制约着STL网格模型的进一步优化处理与应用.为此,需要针对STL网格模型进行网格重建.本文针对2维流形的STL三角形曲面网格模型,提出了一种快速的网格重建方法.主要利用删除在重建过程中达到饱和的顶点,以便减少需要比对的顶点数,并结合STL文件数据的相关性来提高顶点搜索与比较的效率.对于非封闭的曲面网格,本文算法在提高曲面网格重建效率的同时,还能有效地提取曲面网格模型的边界信息.另外,重建的曲面网格数据文件大大地减少了存储空间,有效地去除了冗余数据.实验结果表明本文算法的高效性及鲁棒性.     

一种基于冗余小波变换的DT网格运动估计和运动补偿方法

网格划分和网格顶点的运动估计是基于不规则网格的视频压缩技术的关键。为了进一步提高网格运动估计和运动补偿的效果,在综合比较现有冗余小波变换域运动估计方法和适用规则网格的EMRMC算法的基础上,提出了一种新的基于不规则网格的运动估计和运动补偿算法,即在冗余小波变换域提取特征点和运动潜在区,网格顶点的运动估计采用结合运动潜在区的在时域进行块匹配的运动估计和运动补偿方法,而运动补偿则通过三角形仿射变换完成。同时还给出了冗余小波变换域提取运动潜在区的计算模板。理论分析和实验结果表明,该算法在补偿效果方面较前两种方法得到了改进。     

基于运动图的路径编辑技术

改进了过渡运动的生成算法和路径搜索算法,提出了一种基于运动图的路径编辑的新方法。其中,针对过渡运动的构造,通过最小化融合帧之间的平均帧间距来自动确定用于运动融合的运动片段,并提出了改进动态时间变形(EDTW)算法来解决这一最优化问题;针对运动图上的路径搜索,提出了基于路径曲线所夹面积的目标函数并改进了分段搜索算法和剪枝策略。实验结果表明,该方法能够编辑生成与用户指定路径高度匹配的人物运动。     

基于截面数据的C1插值融合曲面重建

为了避免NURBS曲面重建需要进行节点矢量相容的问题,提出了一种双方向融合插值的[C1]参数曲面重建方法,该方法先后分段插值截面上连续的数据点、截面曲线以构造样条曲线和曲面片,并引入融合算法进行曲线、曲面拼接,从而得到光滑的待建曲面。该方法不会产生由节点插入所带来的大量的数据冗余以及复杂的计算过程,同时采用了融合的思想来处理曲线、曲面的拼接,改良了传统参数曲线、曲面拼接方法需要满足边界条件的缺陷。     

基于RDWT与改进SIFT的DT网格运动估计与补偿*

为进一步提高运动估计和补偿的效果,提出了一种基于RDWT与改进SIFT的DT网格运动估计算法。首先在RDWT域内提取潜在运动区（PMA）,并设计了自适应的特征点提取模板;然后对SIFT算法进行了改进,它能快速进行特征点的精确提取与匹配,进而生成DT网格;最后利用仿射变换在PMA内进行运动估计与补偿。实验表明,该算法能快速有效地提取视频图像的特征点,在保持较高峰值信噪比(PSNR)的情况下提高运动估计的效率,且重建图像的主观质量很好,较现有基于不规则三角网格的运动估计算法在PSNR和效率上有一定优势。     

基于Rough Set的镜头分割方法

综合利用了MPEG视频流P帧的运动特征、像素差和直方图差特征,提出了一种基于Rough Set的镜头分割方法。该方法首先提取视频流中P帧的宏块信息,然后分析得到其运动活力性、宏块类型和运动空间分布,再结合这些帧的像素差特征和直方图差特征,利用Rough Set对这些特征进行约减后,对镜头切换处进行识别。实验表明,该方法能有效地区分镜头的突变,对渐变也能很好地检测。     

虚拟现实中一种基于运动混合的实时同步算法

在虚拟现实中,采用运动捕获系统建立基本运动库,然后通过运动编辑技术对基本运动进行处理。运动混合技术是编辑技术中最为实用也最为复杂的一种。提出了基于运动混合的实时同步算法,以便更好地动态混合运动,避免产生未预期的效果,以创建复杂的虚拟动画。     

Android平台下的实时人体行为识别

为了提高Android平台下实时人体行为识别方法的性能,提出对动作变化和过渡动作进行检测和分割的方法。该方法采用加速度在重力方向上的投影和水平方向上投影的幅值来表征行为活动,通过趋势判断行为变化,结合趋势突变点检测和DTW算法进行过渡动作分割。提取加速度时域特征,使用随机森林对九种行为进行分类识别,平均识别率达到97.26%,其中过渡动作平均识别率达到95.05%。     

过渡目标值的非线性PID对自治水下机器人变深运动的稳定控制

针对传统PID在控制自治水下机器人(autonomous underwater vehicle,AUV)变深运动时易出现超调、大幅波动等问题,提出一种具有过渡目标值过程来调节误差反馈的非线性PID控制器.在分析传统PID控制下系统出现超调原因的基础上,对系统目标值安排过渡过程,利用系统输出跟踪过渡后的目标值进行误差反馈控制.通过赫尔维兹判据证明了系统稳定性,仿真验证了控制的可行性.最后通过湖上试验验证其工程可行性与实用性,得出在非线性过渡目标值的PID控制下,系统的动态响应特性得以优化,变深超调和波动问题明显改善,可实现AUV平稳地变深运动控制.