A Scanline Method for Solid Model Display

The modelling of solid objects is becoming increasingly important in the application of computer graphics to a wide variety of problems, such as CAD/CAM, simulation, and molecular modelling. A variety of methods for rendering solid objects exists, including 2-Buffer, Scanline and Ray Tracing. This paper is concerned with a scanline method for the production of still images of complex objects. The implementation of a scanline algorithm is discussed, in conjunction with a consideration of its performance in relation to the z-buffer method.
Many scanline methods cater only for a restricted class of primitives, such as polygons or spheres, whereas this implementation is a general purpose scanline algorithm capable of being extended to handle a variety of primitives. The primitives currently available are polygons, spheres, spheres swept along straight-line trajectories, and cylinders. Polygonal models of cubes, cones and cylinders are also available.
The approach is capable of dealing with "positive" and "negative" volumes, allowing objects with holes to be modelled and displayed. It has further been extended to cater for the inclusion of transparent objects into a scene, and consequently allows the modelling of coloured "glass" objects.     

A Finite Element Method on Convex Polyhedra

We present a method for animating deformable objects using a novel finite element discretization on convex polyhedra. Our finite element approach draws upon recently introduced 3D mean value coordinates to define smooth interpolants within the elements. The mathematical properties of our basis functions guarantee convergence. Our method is a natural extension to linear interpolants on tetrahedra: for tetrahedral elements, the methods are identical. For fast and robust computations, we use an elasticity model based on Cauchy strain and stiffness warping. This more flexible discretization is particularly useful for simulations that involve topological changes, such as cutting or fracture. Since splitting convex elements along a plane produces convex elements, remeshing or subdivision schemes used in simulations based on tetrahedra are not necessary, leading to less elements after such operations. We propose various operators for cutting the polyhedral discretization. Our method can handle arbitrary cut trajectories, and there is no limit on how often elements can be split.     

A scanline algorithm for displaying trimmed surfaces by using Bézier clipping

Displaying objects with high accuracy is necessary for CAGD (computer-aided geometric design) and for the synthesis of photo-realistic images. Traditionally, polygonal approximation methods have been employed to display free-form surfaces. They bring on low accuracy of display not only in shape, but also in intensity of objects. In this paper, a scanline algorithm to directly display parametric surface patches, expressed by trimmed Bézier surfaces, without polygonal approximation is proposed. In the method proposed here, curved surfaces are subdivided into subpatches with curved edges intersecting with a scanline, and the intersections of every subpatch and the scanline are calculated. This method is extremely robust for calculating the intersections, which can be obtained with only a few iterations; the Bézier clipping method is used for the iteration. Anti-aliased images with shadows and texture mapping are given to show the effectiveness of the method proposed.     

Performance of scanline algorithms for direct display of CSG

Direct display algorithms display a CSG model without first converting the model into a boundary representation. Three such algorithms are described. All three are based on the scanline display algorithm, and are able to handle both polygonal and quadratic faces.The first algorithm is based on Atherton's recursive subdivision scanline algorithm, the second is a combination of a scanline and a ray casting algorithm, and the third is a scanline version of the Trickle algorithm. A multiprocessor system in which these algorithms can be incorporated is also described.The performances of the algorithms are compared. It turns out that the algorithms efficiently display CSG models on general-purpose architectures. A comparison is also made between the performances for polygon-approximated models and exact models for objects bounded by quadratic faces, such as spherical, cylindrical and conical faces, to get an indication of how many polygons can at most be used to approximate quadratic faces and still have better performance.     

单波束前视声纳的信息提取方法研究

介绍了一种可用于小型水下机器人的前视声纳信息提取方法。利用该方法获取了声纳视域内目标的方位信息,这在小型水下机器人的自主目标跟踪和避碰方面具有很大的应用价值。该方法主要包括3个部分的内容:利用声纳数据生成声纳图像;对声纳图像进行预处理;从处理后的图像中提取目标的特征信息。针对图像中较大目标的边缘信息,提出了一种基于最小二乘法的分段曲线拟合的方法,并给出了基于实验室的水池中获得的实测数据的拟合结果,验证了该方法的有效性。     

Localizing overlapping parts by searching the interpretation tree

This paper discusses how local measurements of positions and surface normals may be used to identify and locate overlapping objects. The objects are modeled as polyhedra (or polygons) having up to six degrees of positional freedom relative to the sensors. The approach operates by examining all hypotheses about pairings between sensed data and object surfaces and efficiently discarding inconsistent ones by using local constraints on: distances between faces, angles between face normals, and angles (relative to the surface normals) of vectors between sensed points. The method described here is an extension of a method for recognition and localization of nonoverlapping parts previously described in [18] and [15].     

基于扫描线分段的图像稠密匹配方法

在分析相关视图扫描线特征的基础上,提出了一种基于扫描线分段图像稠密匹配方法。依据灰度特征,将校正图像扫描线划分为灰度相似的像素段,重构以灰度平均的像素段为基元的新扫描线,在计算像素段匹配的基础上进行图像稠密匹配,以降低视图稠密匹配过程中的歧义性,提高匹配效率,最后给出了实验结果。     

压入新、旧区段的区域填充扫描线算法

指出压入区段端点的区域填充扫描线算法对一类特殊4-连通区域有可能产生漏填,利用像素间的相关性和区域在扫描线上的连贯性提出了采用“重写区段左端点”的4向填充方法进行改进;通过分析原算法中仍然存在的像素点颜色判读的重复操作,提出了压入新、旧区段的区域填充扫描线算法并给出算法的描述;典型的填充测试证明了本算法的正确性和高效性。     

Exact and efficient construction of Minkowski sums of convex polyhedra with applications

We present an exact implementation of an efficient algorithm that computes Minkowski sums of convex polyhedra in R³. Our implementation is complete in the sense that it does not assume general position. Namely, it can handle degenerate input, and it produces exact results. We also present applications of the Minkowski-sum computation to answer collision and proximity queries about the relative placement of two convex polyhedra in R³. The algorithms use a dual representation of convex polyhedra, and their implementation is mainly based on the Arrangement package of Cgal, the Computational Geometry Algorithm Library. We compare our Minkowski-sum construction with the only three other methods that produce exact results we are aware of. One is a simple approach that computes the convex hull of the pairwise sums of vertices of two convex polyhedra. The second is based on Nef polyhedra embedded on the sphere, and the third is an output-sensitive approach based on linear programming. Our method is significantly faster. The results of experimentation with a broad family of convex polyhedra are reported. The relevant programs, source code, data sets, and documentation are available at http://www.cs.tau.ac.il/~efif/CD and a short movie [Fogel E, Halperin D. Video: Exact Minkowski sums of convex polyhedra. In: Proceedings of 21st annual ACM symposium on computational geometry. 2005. p. 382-3] that describes some of the concepts portrayed in this paper can be downloaded from http://www.cs.tau.ac.il/~efif/CD/Mink3d.avi.     

Fast Image Correspondence with Global Structure Projection

This paper presents a method for recognizing images with flat objects based on global keypoint structure correspondence.This technique works by two steps:reference keypoint selection and structure projection.The using of global keypoint structure is an extension of an orderless bag-of-features image representation,which is utilized by the proposed matching technique for computation efficiency.Specifically,our proposed method excels in the dataset of images containing "flat objects" such as CD covers,books,newspaper.The efficiency and accuracy of our proposed method has been tested on a database of nature pictures with flat objects and other kind of objects.The result shows our method works well in both occasions.     

一种新的区域种子填充算法

在未知边界的区域种子填充算法中,改进扫描线算法犤1犦具有非常高的填充效率,但它只适用于四连通区域,为此,文章提出了一种新的基于边界跟踪的填充算法,该算法弥补了文献犤1犦算法的不足,可以填充任意的四连通或八连通区域,而在填充效率上仅比其略低几个百分点,因此更具有实际应用性。     

Proximity Queries Between Convex Objects: An Interior Point Approach for Implicit Surfaces

This paper presents a general method for exact distance computation between convex objects represented as intersections of implicit surfaces. Exact distance computation algorithms are particularly important for applications involving objects that make intermittent contact, such as in dynamic simulations and in haptic interactions. They can also be used in the narrow phase of hierarchical collision detection. In contrast to geometric approaches developed for polyhedral objects, we formulate the distance computation problem as a convex optimization problem. We use an interior point method to solve the optimization problem and demonstrate that, for general convex objects represented as implicit surfaces, interior point approaches are globally convergent, and fast in practice. Further, they provide polynomial-time guarantees for implicit surface objects when the implicit surfaces have self-concordant barrier functions. We use a primal-dual interior point algorithm that solves the Karush-Kuhn-Tucker (KKT) conditions obtained from the convex programming formulation. For the case of polyhedra and quadrics, we establish a theoretical time complexity of O(n^1.5), where n is the number of constraints. We present implementation results for example implicit surface objects, including polyhedra, quadrics, and generalizations of quadrics such as superquadrics and hyperquadrics, as well as intersections of these surfaces. We demonstrate that in practice, the algorithm takes time linear in the number of constraints, and that distance computation rates of about 1 kHz can be achieved. We also extend the approach to proximity queries between deforming convex objects. Finally, we show that continuous collision detection for linearly translating objects can be performed by solving two related convex optimization problems. For polyhedra and quadrics, we establish that the computational complexity of this problem is also O(n^1.5).     

Determination of the attitude of 3D objects from a singleperspective view

A method for finding analytical solutions to the problem of determining the attitude of a 3D object in space from a single perspective image is presented. Its principle is based on the interpretation of a triplet of any image lines as the perspective projection of a triplet of linear ridges of the object model, and on the search for the model attitude consistent with these projections. The geometrical transformations to be applied to the model to bring it into the corresponding location are obtained by the resolution of an eight-degree equation in the general case. Using simple logical rules, it is shown on examples related to polyhedra that this approach leads to results useful for both location and recognition of 3D objects because few admissible hypotheses are retained from the interpolation of the three line segments. Line matching by the prediction-verification procedure is thus less complex     

一个可扩展的工作流元模型

文章分析WFMC工作流参考模型的可扩展性,提出了一个可扩展的工作流元模型。该模型分为核心层、初始层和扩展层三个层次,核心层描述工作流的核心概念,初始层用来根据企业的模型建立一些企业个性化的扩展,扩展层则可以根据需求进行动态扩展。该工作流元模型定义了工作流相关对象来抽象企事业模型中的各中对象,可适应不同类型的企事业单位的工作流建模。     

校正图像对视差图计算的一种简化方法

本文提出了一种基于边界流的校正图像对视差图计算的简化方法。本方法通过将校正图像上匹配扫描线对划分为灰度相似的象素段,以灰度平均的像素段为基元构造新扫描线,在计算像素段匹配的基础上进行匹配计算,以降低视差图计算过程中的歧义性,提高匹配效率。     

Delegation by object composition

Class inheritance and method overriding, as provided by standard class-based languages, are often not flexible enough to represent objects with some dynamic behavior. In this respect, object composition equipped with different forms of method body lookup is often advocated as a more flexible alternative to class inheritance since it takes place at run time, thus permitting the behavior of objects to be specialized dynamically. In this paper, we illustrate Incomplete Featherweight Java (IFJ), an extension of Featherweight Java with a novel linguistic construct, the incomplete object. Incomplete objects require some missing methods which can be provided at run time by composition with another (complete) object. Furthermore, we present two mechanisms for the method body lookup on (composed) objects, one based on delegation and the other based on consultation. Thanks to the design of the language, the consultation-based lookup is a simple extension of the delegation-based one. Both mechanisms are disciplined by static typing, therefore the language enjoys type safety (which implies no “message-not-understood” run-time errors) and avoids possible accidental overrides due to method name clashes.     

基于颜色直方图的EM对象跟踪算法

基于均值漂移运动目标跟踪的迭代算法,简单可靠,可以方便准确的找到一个基于内核的概率密度函数估计目标的位置。但是该算法对目标尺寸形状变化的适应能力比较差,文章提出一个改进的均值漂移算法。新算法同时估计目标的位置和用协方差矩阵来描述的目标的形状,能够处理对象的角度和形状大小发生变化时的跟踪问题,运用新的算法实现以颜色直方图为基础的非刚性目标跟踪算法。实验表明,该改进的算法在不同环境下跟踪目标的鲁棒性很好,尤其对跟踪目标的形状和尺寸的改变,具有很强的适用性。     

AC-HAPE3D：基于强化学习的异形填充算法

在3D打印、快递物流等领域,需要将形状各异的零件或货物在限定的空间中摆放,称为异形填充。给出一种摆放方案,以便将尽可能多的多面体放入给定容器;或者一批物体紧密地摆放,使得占用体积最小,则称为异形填充问题。这是个NP问题,很难高效求解。基于此,研究在一个可变维度的三维容器内摆放给定的一组多面体,使得打包后容器的可变维度最小。并提出一个基于强化学习的算法AC-HAPE3D,利用启发式算法HAPE3D将问题建模为马尔可夫过程,再利用基于策略的强化学习方法 Actor-Critic进行学习。同时用体素来表示容器和多面体,从而简化状态信息的表达,并用神经网络表示价值函数和策略函;为了解决状态信息长度以及动作空间可变的问题,采取遮罩的方法来屏蔽部分输入和输出,并且引入LSTM来处理变长的状态信息。在5个不同的数据集进行的实验表明算法能够取得较好的结果。     

Methods of search for stable solutions of some optimization problems in the theory of recognition by precedents

In constructing some models of recognition algorithms, there arise a number of optimization problems. The search for the optimal consistent subsystem of a given system of linear inequalities plays an important role in the process of data analysis in the theory of recognition by precedent. The optimality of a required subsystem is defined by a number of the conditions imposed on it. Earlier the author developed several algorithms for solving the problems of this type. These algorithms are based on exhaustive search for nodal subsystems of a given system of linear inequalities. In the search for optimal consistent subsystem, these algorithms find boundary decisions. However, in practical application often it is necessary to find a stable solution. So, when looking for logical regularities of a special type, it is required to find a set of non-degenerate polyhedra describing a certain class of objects in a space of features. Therefore, linear inequalities systems corresponding to these polyhedra must be stable. In this paper, we propose a method for modifying the previously developed algorithms to select the stable consistent subsystem of highest possible power and find its stable solution.     

特性关系粗糙集中对象变化时近似集增量更新方法研究

特性关系信息系统是一般信息系统的推广模型,仅满足自反性,具有同时处理不完备信息系统中的丢失数据和不关心数据的功能。在实际应用中,信息系统随着对象的变化而不断地动态变化。研究了在特性关系粗糙集模型下单个对象增加和删除时近似集变化的规律,提出了相应的增量更新算法并给予了实验验证。