Matrix-valued 4-point spline and 3-point non-spline interpolatory curve subdivision schemes

The objective of this paper is to study and construct matrix-valued templates for interpolatory curve subdivision. Since our investigation of this problem was motivated by the need of such subdivision stencils as boundary templates for interpolatory surface subdivision, we provide both spline and non-spline templates that are necessarily symmetric, due to the lack of direction-orientation in carrying out surface subdivision in general. For example, the minimum-supported Hermite interpolatory C¹ cubic spline curve subdivision scheme, with the skew-symmetric basis function for interpolating first derivatives, does not meet the symmetry specification. Non-spline C² interpolatory templates constructed in this paper are particularly important, due to their smaller support needed to minimize undesirable surface oscillations, when adopted as boundary templates for interpolatory C² surface subdivision. The curve subdivision templates introduced in this paper are adopted as boundary stencils for interpolatory surface subdivision with matrix-valued templates.     

基于双参数四点细分法的曲面造型

将双参数四点细分曲线方法进行推广，提出了基于双参数四点细分法的曲面造型方法，并对其收敛性进行了分析。该方法通过对两个参数的适当调节能够较容易地控制极限曲面的形状，极限曲面能够达到C4连续，可以应用到对曲面的连续性要求较高的曲面造型中去。在给定初始数据的条件下，可通过对形状参数的适当选择来实现对极限曲面的形状调整和控制，试验表明该算法生成光滑曲面是有效的。     

一种基于序列图像的交互式快速三维重建方法

针对普通数码相机拍摄的序列图像,提出了一种快速的交互式三维重建方法.首先基于SFM技术得到了相机的内外部参数;然后在图像上交互取点以构建逼近物体轮廓的多边形,结合该多边形,利用轮廓跟踪算法提取出精确的外形轮廓;最后通过匹配轮廓点的方式重建出三维模型.实验结果表明该重建方法是快速而有效的.     

Reconstruction of 3D human body pose from stereo image sequences based on top-down learning

This paper presents a novel method for reconstructing a 3D human body pose from stereo image sequences based on a top-down learning method. However, it is inefficient to build a statistical model using all training data. Therefore, the training data is hierarchically divided into several clusters to reduce the complexity of the learning problem. In the learning stage, the human body model database is hierarchically constructed by classifying the training data into several sub-clusters with silhouette images. The data of each cluster in the bottom level is represented by a linear combination of examples. In the reconstruction stage, the proposed method hierarchically searches a cluster for the best matching silhouette image using a silhouette history image (SHI). Then, the 3D human body pose is reconstructed from a depth image using a linear combination of examples method. By using depth information to reconstruct 3D human body pose, the similar poses in silhouette images are estimated as different 3D human body poses. The experimental results demonstrate that the proposed method is efficient and effective for reconstructing 3D human body poses.     

OpenGL在逆向工程三维重构中的应用研究

研究了在MFC中运用OpenGL进行编程，重构三维物体的方法，对于逆向工程三维重构的杂乱离散点云，在进行排序重组和三角网格化后，运用OpenGL对三角网格进行消隐，设定法线，光照和材质的处理，重构原始物体，具体的应用实例说明了所提方法的有效性。     

Constructing Isosurfaces from 3D Data Sets Taking Account of Depth Sorting of Polyhedra

Creating and rendering intermediate geometric primitives is one of the approaches to visualisze data sets in 3D space.Some algorithms have been developed to construct isosurface from uniformly distributed 3D data sets.These algorithms assume that the function value varies linearly along edges of each cell.But to irregular 3D data sets,this assumption is inapplicable.Moreover,the detth sorting of cells is more complicated for irregular data sets,which is indispensable for generating isosurface images or semitransparent isosurface images,if Z-buffer method is not adopted.In this paper,isosurface models based on the assumption that the function value has nonlinear distribution within a tetrahedron are proposed.The depth sorting algorithm and data structures are developed for the irregular data sets in which cells may be subdivided into tetrahedra.The implementation issues of this algorithm are discussed and experimental results are shown to illustrate potentials of this technique.     

Physical sketching: Reconstruction and analysis of 3D objects from freehand sketches

When designing a 3D object, designers, engineers and teachers often begin investigating potential design tradeoffs by creating informal sketches. Ideally, these sketches-in combination with a variety of engineering analysis tools-would allow prediction of the object’s physical properties, especially those that affect the critical early design process. We introduce a pen-based system that reconstructs 3D spatial geometry from a single 2D freehand-sketch consisting of straight and curved lines in interactive time. Several optimization-based approaches to this problem have been proposed, but these generally have difficulty converging to an acceptable solution because the dimensionality of the search space is large. The primary contribution of this paper is a new reconstruction algorithm for orthographic projections of 3D wireframes. The algorithm reconstructs the depths of each vertex by exploiting geometric regularities among the graph lines in a reduced solution space, then optimizes a cost function over this space to recover the vertex depths. A second optimization algorithm is used to infer the 3D geometry of curved strokes once the vertex depths have been recovered. The proposed approach can recover the geometry of several objects with approximately 50 curved strokes in near interactive time. We also present an iterative, Tablet-PC-based design system that uses the proposed reconstruction algorithm to recover 3D objects from 2D orthographic sketches. The system allows the reconstructed objects to be subjected to two types of physical analysis, the results of which are superimposed directly on the sketch: a fast, kinematic simulation, and a complete finite-element-based static analysis. The object can quickly be modified in place using the pen-based interface according to the results of the analysis to allow for iterative design work. We demonstrate the system in action on a variety of early-stage design analyses.     

由单幅二维灰度图像重构物体表面形状*

鉴于目前很少有论文讨论完整的由单幅二维灰度图像重构物体表面形状的算法,包括它的控制参数的估计及算法的实现,介绍了一种完整的SFS算法.它在考虑自遮掩影响的情况下,有效地估计了SFS算法中涉及的各种控制参数,并引入亮度约束、灰度梯度约束和可积性约束,计算出表面高度和表面向量,实现三维重构.与传统的算法相比,本算法无论是在速度还是在精度方面都达到了比较高的水平,具有一定的应用前景.最后还指出了在MATLAB中实现需要注意的问题.     

视觉图像三维重构计算一般性框架研究

三维实体数字图像重构建模是当前计算机视觉研究领域的热点课题,涉及到相机标定、对应点匹配和三维重构计算等关键技术.本文回顾了三维重构建模的研究现状,分析了现有理论和方法在实际应用中存在的问题;在此基础上进行了相关研究,总结出了三维重构计算的一般性框架,提出了一些研究观点和方法,并探讨了三维重构技术的难点和发展趋势.     

A 2-point algorithm for 3D reconstruction of horizontal lines from a single omni-directional image

Reconstruction of 3D scenes with abundant straight line features has many applications in computer vision and robot navigation. Most approaches to this problem involve stereo techniques, in which a solution to the correspondence problem between at least two different images is required. In contrast, 3D reconstruction of straight horizontal lines from a single 2D omni-directional image is studied in this paper. The authors show that, for symmetric non-central catadioptric systems, a 3D horizontal line can be estimated using only two points extracted from a single image of the line. One of the two points is the symmetry point of the image curve of horizontal line, and the other is a generic point on the image curve. This paper improves on several prior works, including horizontal line detection in omni-directional image and line reconstruction from four viewing rays, but is simpler than those methods while being more robust. We evaluate how the precision of feature point extraction can affect line reconstruction accuracy, and discuss preliminary experimental results.     

三维表面重构过程参数的估计研究

在SFS(基于阴影的三维表面重构)各种算法中,都需要光源方向及曲面反射率。这些参数与图像的恢复效果息息相关。针对这些参数,也应运而生了各种各样的行之有效的方法。论文讨论了两种有效的算法,利用合成图像分别进行试验,并对其优缺点和运行效率进行比较,从而为进一步的SFS算法研究提供有价值的参考。     

计算机视觉中的三维重构建模

三维重构建模是计算机视觉技术的主要内容之一。相机内外参数的标定、图像特征点的提取以及特征点的立体匹配是三维重构建模的技术核心。本文总结了近来三维重构建模的研究成果和计算方法,并提出了一些观点,对三维重构建模的难点和发展趋势作了说明。     

岩石样本孔隙和颗粒二维图象的三维重建研究

在石油地质图象分析和模式识别中,三维物体重建是很重要的研究。该文研究了岩石样本孔隙和颗粒二维图象三维重建的一种新方法。这种方法利用从二维薄片取得的岩相学图象信息,用图象处理理论技术和数学形态学的方法生成了岩石的三维模型,对重建的三维微观结构和实际砂岩的表面细微结构进行了定量比较,比较显示,这种重建方法得到的三维模型孔隙率与原始图象基本一致,其水平面/纵切面/横切面上的颗粒长径分布与实际岩石有较好的相关性。     

基于邻边推理求隐藏元素的正等轴测图3D重建

针对正等轴测图3D重建中的隐藏元素求解，通过模拟人类的认知思维，提出了基于邻边推理求隐藏元素的算法。隐藏元素的推理就是通过对正等轴测图中含有隐藏边的点进行推理，根据其相邻边、过相邻点的边的方向和长度推理出可能的隐藏点集，然后根据重合性及连边规则对可能的隐藏点集进一步求解，得到隐藏元素的坐标信息和连边规则。深度推理算法就是用点的坐标信息和边的长度、角度信息推理每个点、边的深度。由C 工具和OpenGL技术开发的To3D验证了上述算法，证明该算法对平面立体的隐藏元素推理和重建十分有效。     

双目视觉的台球桌面的三维重构

随着计算机技术的迅猛发展,在越来越多的体育比赛中纷纷出现了电子裁判来辅助裁判进行判罚工作,以实现奥林匹克的公平竞赛精神.而在实现这种数字化裁判的过程中,摄像机在计算机视觉中起着重要的作用,三维重构就是根据单视图或者多视图的图像重建三维信息的过程.主要以计算机视觉中的三维重构技术作为研究对象,具体详述了有关双目视觉的一些理论知识,充分利用计算机视觉库OpenCV提供的重建算法,来完成对台球桌面的三维重构工作.台球桌面的三维重构具有很强的现实意义,为电子裁判进入桌球比赛打下了良好的基础.     

Volumetric Model Reconstruction from Unrestricted Camera Views Based on the Photo-consistency of 3D Voxel Mask

This project aims to develop a three-dimensional (3D) model reconstruction system using images acquired from a mobile camera. It consists of four major steps: camera calibration, volumetric model reconstruction, surface modeling and texture mapping. A novel online scale factor estimation is developed to enhance the accuracy of the coplanar camera calibration. For the volumetric modeling, the voting-based shape-from-silhouette first generates a coarse model, which is then refined by the photo-consistency check using the novel 3D voxel mask. Our scheme can handle concave surface in a sophisticated way. Finally, the surface model is formed with the original images mapped. 3D models of some test objects are presented.     

State of the Art on Monocular 3D Face Reconstruction,Tracking, and Applications

The computer graphics and vision communities have dedicated long standing efforts in building computerized tools for reconstructing, tracking, and analyzing human faces based on visual input. Over the past years rapid progress has been made, which led to novel and powerful algorithms that obtain impressive results even in the very challenging case of reconstruction from a single RGB or RGB‐D camera. The range of applications is vast and steadily growing as these technologies are further improving in speed, accuracy, and ease of use. Motivated by this rapid progress, this state‐of‐the‐art report summarizes recent trends in monocular facial performance capture and discusses its applications, which range from performance‐based animation to real‐time facial reenactment. We focus our discussion on methods where the central task is to recover and track a three dimensional model of the human face using optimization‐based reconstruction algorithms. We provide an in‐depth overview of the underlying concepts of real‐world image formation, and we discuss common assumptions and simplifications that make these algorithms practical. In addition, we extensively cover the priors that are used to better constrain the under‐constrained monocular reconstruction problem, and discuss the optimization techniques that are employed to recover dense, photo‐geometric 3D face models from monocular 2D data. Finally, we discuss a variety of use cases for the reviewed algorithms in the context of motion capture, facial animation, as well as image and video editing.     

单幅图像三维表面重建的算法研究与实现

以单幅二维图像为研究对象,应用SFS的基本理论,首先对二维图像进行了光照的倾角和偏角的估计,在光源坐标系下计算出物体每一点的表面梯度;之后,旋转坐标系,在观察坐标系下得到物体的表面梯度;最后采用三点辛普森公式求出物体表面的高度。整个算法流程简单,求解层次分明,重构满意度较高。     

A study on the 3D position estimation of ventricular borders extracted from 2D echocardiography data

We study on the reconstruction of 3D left ventricle(LV) using only 2D echocardiography data and information on apical long-axis views. Especially, this paper focuses on determining the 3D position of LV contours extracted from 2D echocardiography images. First we mathematically model the relationship between LV contours on the apical views and their corresponding 3D positions. The relationship is expressed as a linear equation in which the right-hand side is the measured data consisting of all the LV contour points on each view and the coefficient matrix is an unknown matrix that transforms the unknown 3D positions into contour points on their related apical view, with distance and orthogonality conditions on the coefficient matrix and the 3D positions. Next we consider a non-convex constrained minimization problem to determine the coefficient matrix and the 3D positions. To solve this minimization problem, we adopt two block coordinate descent method with a solver in OPTI for quadratically constrained quadratic program. For validating the proposed method, some numerical experiments are performed with synthetic data. The experimental results show that the proposed model is promising and available for real echocardiographydata.     

Quantitative assessment of the effectiveness of using display techniques with a haptic device for manipulating 3D objects in virtual environments

Quantitative assessment is made of using two display techniques, providing two different levels of depth perception, in conjunction with a haptic device for manipulating 3D objects in virtual environments. The two display techniques are 2D display, and interactive 3D stereoscopic virtual holography display on a zSpace tablet. Experiments were conducted, by several users of different ages and computer training. The experiments involved selected pointing and manipulation tasks. The speed of performing the tasks using the two display techniques were recorded. Statistical analysis of the data is presented. As expected, the use of interactive 3D stereoscopic display resulted in faster performance of the tasks. The improvement in performance was particularly noticeable for the cases wherein the subjects needed to manipulate the haptic arm to reach objects/targets at different depths, and also when the objects/targets were occluded partially by the obstacles.