Progressive Hulls for Intersection Applications

Progressive meshes are an established tool for triangle mesh simplification. By suitably adapting the simplification process, progressive hulls can be generated which enclose the original mesh in gradually simpler, nested meshes. We couple progressive hulls with a selective refinement framework and use them in applications involving intersection queries on the mesh. We demonstrate that selectively refinable progressive hulls considerably speed up intersection queries by efficiently locating intersection points on the mesh. Concerning the progressive hull construction, we propose a new formula for assigning edge collapse priorities that significantly accelerates the simplification process, and enhance the existing algorithm with several conditions aimed at producing higher quality hulls. Using progressive hulls has the added advantage that they can be used instead of the enclosed object when a lower resolution of display can be tolerated, thus speeding up the rendering process. ACM CSS: I.3.3 Computer Graphics—Picture/Image Generation, I.3.5 Computer Graphics—Computational Geometry and Object Modeling, I.3.7 Computer Graphics—Three‐Dimensional Graphics and Realism     

求平面点集凸壳的一种新算法

在研究了大量的求平面点集凸包的算法基础上,提出了一种新的构造平面点集的凸壳算法。此算法先求出四个极值点,构造出一个四边形。对于四边形外面的点依次用二分法进行判断是属于哪个线段区域;对于一个线段区域上的点只需要找出右侧的点,分别和线段的两个端点连接得到新的多边形链,依次这样处理每个点,直到结束。这样就得到四个简单多边形单调链,然后对单调链求凸点,时间复杂度为O（n）,最后求得的每个凸点就是平面点集的凸壳,此算法总的时间复杂度不超过O（n log n）。     

The integration of the output controllability index within the dynamic operability framework in process system design

This paper presents the integration of the output controllability index within the dynamic operability framework to facilitate controllability and economic assessment of process system design for regulatory cases. The framework utilises the geometric representation of feasible operating region as well as input, output and disturbance spaces, in terms of their convex hulls. The geometric operations amongst these convex hulls replace most of the inequalities on the original framework. In addition to the best feasible operating conditions, which are the original outcome, the framework also provides a controllability index involving all of the output variables (generalised integral absolute error, GIAE) and the expected variation of profit on disturbance rejection dynamics. The applicability of the proposed framework is demonstrated on a nonlinear chemical process system with a fixed control structure.     

Mending broken vessels a fusion between color markings and anchor points on surface breaks

This paper presents a method to assist in the tedious process of reconstructing ceramic vessels from excavated fragments. The method exploits vessel surface marking information coupled with a series of generic models constructed by the archaeologists to produce a virtual reconstruction of what the original vessel may have looked like. Generic models are generated based on the experts’ historical knowledge of the period, provenance of the artifact, and site location. The generic models need not to be identical to the original vessel, but must be within a geometric transformation of it in most parts. By aligning the fragments against the generic models, the ceramic vessels are virtually reconstructed. The alignment is based on a novel set of weighted discrete moments computed from convex hulls of the markings on the surface of the fragments and the generic vessels. When the fragments have no markings on them, they are virtually mended to abutting fragments using intrinsic differential anchor points computed on the surface breaks and aligned using a set of absolute invariants. For axially symmetric objects, a global constraint induced by the surface of revolution is added to guarantee global mending consistency.     

A magnetic climbing robot to perform autonomous welding in the shipbuilding industry

In this paper we present the mechanical and control design of a magnetic tracked mobile robot. The robot is designed to move on vertical steel ship hulls and to be able to carry 100 kg payload, including its own weight. The mechanical components are presented and the sizing of the magnetic tracks is detailed. All computation is embedded in order to reduce time delays between processes and to keep the robot functional even in case of signal loss with the ground station. The main sensor of the robot is a 2D laser scanner, that gives information on the hull surface and is used for several tasks. We focus on the welding task and expose the control algorithm that allows the robot to follow a straight line for the welding process.     

Workload balancing in distributed crowd simulations: the partitioning method

The simulation of large crowds of autonomous agents with a realistic behavior is still a challenge for several computer research communities. Distributed architectures can provide scalability to crowd simulations, but they require the use of efficient partitioning methods. Although convex hulls have been shown as very efficient structures for crowd partitioning, providing efficient workload balancing to large scale simulations is still an open issue. In this paper, we propose the integration of a workload balancing technique for crowd simulations within a partitioning method based on convex hulls. The region-based balancing technique reassigns agents to servers using a criterion of distance. The performance evaluation results show that this technique ensures the saturation avoidance of the servers in an homogeneous distributed system. This feature can increase the scalability of crowd simulations.     

基于凸壳的约束信息扩展方法

提出了一种新的约束信息扩展方法。该方法先利用给定的标记信息建立凸壳,然后扫描整个数据集,选择在凸壳内的数据点作为候选集并做进一步判断;对于凸壳间的公共数据,采用凸多边形最优三角剖分的方法来确定这些数据最终应加入的标记信息集。该约束信息扩展方法在四类数据集上验证了算法的有效性。     

Climbing robots for maintenance and inspections of vertical structures—A survey of design aspects and technologies

The maintenance and inspection of large vertical structures with autonomous systems is still an unsolved problem. A large number of different robots exist which are able to navigate on buildings, ship hulls or other human-made structures. But, most of these systems are limited to special situations or applications. This paper deals with different locomotion and adhesion methods for climbing robots and presents characteristics, challenges and applications for these systems. Based on a given set of requirements these principles are examined and in terms of a comprehensive state-of-the-art more than hundred climbing robots are presented. Finally, this schematics is applied to design aspects of a wall-climbing robot which should be able to inspect large concrete buildings.     

一种高效的服务组合优化算法

随着功能性属性相同而非功能性属性各异的Web服务的大量涌现,如何在服务组合业务流程中为各个任务选择相应的组件服务以达到组合服务的QoS(quality of service)最大化,并在此基础上满足不同用户的需求,已成为了国内外研究的热点.由于该问题的复杂性(NP-hard),目前存在的大多数方法都并不十分适合需要相对精确、实时决策的Web服务组合系统.因此,本文提出了一种基于凸包构建的组合服务优化算法(CM-HEU)用以解决QoS感知的服务组合优化问题.CM-HEU首先通过对组合服务中的每组任务进行凸包构建,以减少搜索空间.然后通过对初始解向量的多次升级和一次降级操作以达到全局优化的目标.实验表明:相对于现阶段存在的一些主流方法,CM-HEU不仅能得到一个比较理想的结果,并且具有良好的效率.     

Low-degree approximation of high-degree B-spline surfaces

In this paper, a method for approximate conversion of high degree Bezier and B-spline surfaces to lower degree representations is presented to facilitate the exchange of surface geometry between different geometric modeling systems. Building on previous work on curve approximation, the method uses adaptive sampling to compute approximation error and lofting of isoparametric curves to produce the approximating surface. In addition, a bound for the approximation accuracy is computed using convex hulls.     

基于时空显著性的双核KCF目标跟踪算法

传统的核相关滤波器跟踪算法(KCF)在模板更新上容易出现跟踪误差累计,从而导致目标跟踪过程中出现跟踪漂移问题。针对该问题,提出了一种时空显著性的双核KCF目标跟踪的方法。该算法引入了一种时空显著性方法来搜索目标区域的显著特征和姿态稳定的局部区域。利用该局部区域对跟踪过程中产生的累计误差有较低的敏感度特性,能够减少跟踪过程中的累计误差。然后再结合原目标和显著区域建立一个双核跟踪机制,在跟踪过程中不断对原目标跟踪结果进行微调,降低跟踪累计误差。此外,针对快速运动的目标相邻帧偏移量较大的问题,提出了一种锚点预测机制,使得跟踪锚点与目标位置更接近,能够更准确地跟踪到目标。在大型公共数据上测试的实验结果表明,提出的算法在光照、遮挡、变形、快速运动、旋转以及背景杂波等复杂情况下,均具有较强的适应性。     

Reduced Depth and Visual Hulls of Complex 3D Scenes

Depth and visual hulls are useful for quick reconstruction and rendering of a 3D object based on a number of reference views. However, for many scenes, especially multi‐object, these hulls may contain significant artifacts known as phantom geometry. In depth hulls the phantom geometry appears behind the scene objects in regions occluded from all the reference views. In visual hulls the phantom geometry may also appear in front of the objects because there is not enough information to unambiguously imply the object positions. In this work we identify which parts of the depth and visual hull might constitute phantom geometry. We define the notion of reduced depth hull and reduced visual hull as the parts of the corresponding hull that are phantom‐free. We analyze the role of the depth information in identification of the phantom geometry. Based on this, we provide an algorithm for rendering the reduced depth hull at interactive frame‐rates and suggest an approach for rendering the reduced visual hull. The rendering algorithms take advantage of modern GPU programming techniques. Our techniques bypass explicit reconstruction of the hulls, rendering the reduced depth or visual hull directly from the reference views.     

用兴趣点凸包和SVM加权反馈实现图像检索

针对采用环状颜色直方图的图像检索方法存在的不足,提出一种基于兴趣点凸包的图像特征提取方法,通过对用小波变换检测出的必趣点递归求出它们的凸包,并将每个凸包上的兴趣点按一定的算法安插在相应的桶内,对每个桶求出颜色直方图,利用桶与桶之间的相似度定义两幅图像的相似度.这种特征提取方法可有效抑制兴趣点集合中出现游离兴趣点的情况,结合基于兴趣点的空间离散度和Gabor小波纹理等特征实现图像检索,可有效提高图像检索精度.最后,提出一种新的相关反馈方法,通过利用支持向量机分类结果设置权值来改进移动查询点相关反馈方法.实际图像数据库上的实验表明,引入这种反馈方法后可将图像检索的查准率提高20%左右,查全率提高10%左右.     

Monocular 3D tracking of deformable surfaces using sequential second order cone programming

Reconstructing structures of deformable objects from monocular image sequences is important for applications like visual servoing and augmented reality. In this paper, we propose a method to recover 3D shapes of deformable surfaces using sequential second order cone programming (SOCP). The key of our approach is to represent the surface as a triangulated mesh and introduce two sets of constraints, one for model-to-image keypoint correspondences which are SOCP constraints, another for retaining the original lengths of the mesh edges which are non-convex constraints. In the process of tracking, the surface structure is iteratively updated by solving sequential SOCP feasibility problems in which the non-convex constraints are replaced by a set of convex constraints over a local convex region. The shape constraints used in our approach is more generic than previous methods, that enables us to reliably recover surface shapes with smooth, sharp and other complex deformations. The capability and efficiency of our approach are evaluated quantitatively with synthetic image sequences and qualitatively with real image sequences.     

Convex hull based skew estimation

Skew estimation and page segmentation are the two closely related processing stages for document image analysis. Skew estimation needs proper page segmentation, especially for document images with multiple skews that are common in scanned images from thick bound publications in 2-up style or postal envelopes with various printed labels. Even if only a single skew is concerned for a document image, the presence of minority regions of different skews or undefined skew such as noise may severely affect the estimation for the dominant skew. Page segmentation, on the other hand, may need to know the exact skew angle of a page in order to work properly. This paper presents a skew estimation method with built-in skew-independent segmentation functionality that is capable of handling document images with multiple regions of different skews. It is based on the convex hulls of the individual components (i.e. the smallest convex polygon that fully contains a component) and that of the component groups (i.e. the smallest convex polygon that fully contain all the components in a group) in a document image. The proposed method first extracts the convex hulls of the components, segments an image into groups of components according to both the spatial distances and size similarities among the convex hulls of the components. This process not only extracts the hints of the alignments of the text groups, but also separate noise or graphical components from that of the textual ones. To verify the proposed algorithms, the full sets of the real and the synthetic samples of the University of Washington English Document Image Database I (UW-I) are used. Quantitative and qualitative comparisons with some existing methods are also provided.     

Cover geometry design using multiple convex hulls

We present a design method to create close-fitting customized covers for given three-dimensional (3D) objects such as cameras, toys and figurines. The system first computes clustering of the input vertices using multiple convex hulls, then generates multiple convex hulls using the results. It then outputs a cover geometry to set union operation of these hulls, and the resulting intersection curves are set as seam lines. However, as some of the regions created are not necessarily suitable for flattening, the user can design seam lines by drawing and erasing. The system flattens the patches of the target cover geometry after segmentation, allowing the user to obtain a corresponding 2D pattern and sew the shapes in actual fabric. This paper’s contribution lies in its proposal of a clustering method to generate multiple convex hulls, i.e., a set of convex hulls that individually cover part of the input mesh and together cover all of it. The method is based on vertex clustering to allow handling of mesh models with poor vertex connectivity such as those obtained by 3D scanning, and accommodates conventional meshes with multiple connected components and point-based models with no connectivity information. Use of the system to design actual covers confirmed that it functions as intended.     

A comparative study of partitioning methods for crowd simulations

The simulation of large crowds of autonomous agents with realistic behavior is still a challenge for several computer research communities. In order to handle large crowds, some scalable architectures have been proposed. Nevertheless, the effective use of distributed systems requires the use of partitioning methods that can properly distribute the workload generated by agents among the existing distributed resources.In this paper, we analyze the use of irregular shape regions (convex hulls) for solving the partitioning problem. We have compared a partitioning method based on convex hulls with two techniques that use rectangular regions. The performance evaluation results show that the convex hull method outperforms the rest of the considered methods in terms of both fitness function values and execution times, regardless of the movement pattern followed by the agents. These results show that the shape of the regions in the partition can improve the performance of the partitioning method, rather than the heuristic method used.     

Multidimensional Data Visualization Based on the Minimum Distance Between Convex Hulls of Classes

The problem of data visualization in the analysis of two classes in a multidimensional feature space is considered. The two orthogonal axes by which the classes are maximally separated from each other are found in the mapping of classes as a result of linear transformation of coordinates. The proximity of the classes is estimated based on the minimum-distance criterion between their convex hulls. This criterion makes it possible to show cases of full class separability and random outliers. A support vector machine is used to obtain orthogonal vectors of the reduced space. This method ensures the obtaining of the weight vector that determines the minimum distance between the convex hulls of classes for linearly separable classes. Algorithms with reduction, contraction, and offset of convex hulls are used for intersecting classes. Experimental studies are devoted to the application of the considered visualization methods to biomedical data analysis.     

一种可见外壳生成算法

提出了一种可见外壳(visual hulls)生成算法.该算法充分发挥了自适应采样距离场(adaptively sampled distance fields,简称ADFs)表示物体时在逼近精度和内存消耗方面的优越性.与传统的通过体素求交生成可见外壳的方法不同,该算法引入ADFs作为描述可见外壳的采样距离场的空间数据组织形式,从而极大地简化了求交运算,提高了算法的效率.最后通过改进的SurfaceNets算法,将可见外壳的ADF表示转化为面片表示.实验结果表明,该算法可以快速地生成具有较高精度的复杂模型.     

Ship Hulls, B-Spline Surfaces, and CAD/CAM

This integrated CAD/CAM system uses B-spline surfaces to model ship hulls and uses the resulting surface for the production of wooden towing tank models.