A Note on Point Location in Delaunay Triangulations of Random Points

This short note considers the problem of point location in a Delaunay triangulation of n random points, using no additional preprocessing or storage other than a standard data structure representing the triangulation. A simple and easy-to-implement (but, of course, worst-case suboptimal) heuristic is shown to take expected time O(n ^1/3 ) . Received November 27, 1997; revised February 15, 1998.     

Reconfiguring system hierarchies with multi-valued logic

We propose a mathematical formalism to define a system hierarchy and choose a way to reconfigure it based on multi-valued logic. We consider an application of this formalism to control over a group surveying the danger zone after a natural disaster.     

Reconfiguring wireless phones with adaptive chips

Cellular phone manufacturers are on the horns of a dilemma. On one hand, the demand for their products continues to grow. On the other hand, cellular-phone technology is also changing rapidly. Vendors are dealing with this problem by using an adaptive (also called reconfigurable) chips in a new way. With this approach, software can redraw a chip's physical circuitry on the fly, letting a single processor perform multiple functions. In addition, adaptive computing could increase performance while reducing energy consumption.     

Fast Range Searching with Delaunay Triangulations

This paper studies the idea of answering range searching queries using simple data structures. The only data structure we need is the Delaunay Triangulation of the input points. The idea is to first locate a vertex of the (arbitrary) query polygon and walk along the boundary of the polygon in the Delaunay Triangulation and report all the points enclosed by the query polygon. For a set of uniformly distributed random points in 2-D and a query polygon the expected query time of this algorithm is O(n ^1/3 + Q + E K + L _r n ^1/2), where Q is the size of the query polygon , {\bf E}K = O(n\bcdot area is the expected number of output points, L _r is a parameter related to the shape of the query polygon and n, and L _r is always bounded by the sum of the edge lengths of . Theoretically, when L _r = O(1/n^1/6) the expected query time is O(n^1/3 + Q + E K), which improves the best known average query time for general range searching. Besides the theoretical meaning, the good property of this algorithm is that once the Delaunay Triangulation is given, no additional preprocessing is needed. In order to obtain empirical results, we design a new algorithm for generating random simple polygons within a given domain. Our empirical results show that the constant coefficient of the algorithm is small, at least for the special (practical) cases when the query polygon is either a triangle (simplex range searching) or an axis-parallel box (orthogonal range searching) and for the general case when the query polygons are generated by our new polygon-generating algorithms and their sizes are relatively small.     

一种边缘点特征图像配准算法

为解决图像的精确配准问题,提出了结合LoG算法的特征点的提取方法,并将尺度不变特征算法(SIFT)应用到图像的特征描述中.首先利用LoG算法计算边缘点,对边缘点的梯度值进行排序,选择梯度较大的点作为特征点;然后采用SIFT计算特征点的特征向量,利用最小距离算法找到两幅图像的匹配点对;最后利用最相关点和次相关点比例的方法排除错误的点对.实验结果证明,算法对具有光照、角度不同的两组图像能够实现精确的配准,准确率超过90％.     

Optimal Coding and Sampling of Triangulations

We present a bijection between the set of plane triangulations (aka maximal planar graphs) and a simple subset of the set of plane trees with two leaves adjacent to each node. The construction takes advantage of Schnyder tree decompositions of plane triangulations. This bijection yields an interpretation of the formula for the number of plane triangulations with n vertices. Moreover, the construction is simple enough to induce a linear random sampling algorithm, and an explicit information theory optimal encoding. Finally, we extend our bijection approach to triangulations of a polygon with k sides with m inner vertices, and develop in passing new results about Schnyder tree decompositions for these objects.     

Reconfiguring Evidence: Interacting with Digital Objects in Scientific Practice

This paper analyzes how scientists working in a multidisciplinary team produce scientific evidence through building and manipulating scientific visualizations. The research is based on ethnographic observations of scientists’ weekly work meetings and the observation of videotapes of these meetings. The scientists observed work with advanced imaging technologies to produce a 4D computer model of heat transfer in human prostate tissues. The idea of ‘digital objects’ is proposed in order to conceptually locate their ‘materiality’, observed in the practices of producing evidence through the handling of three-dimensional renderings of data. The manipulation of digital objects seeks to establish meaningful differences between parameters of interest, both when building and when analyzing them. These digital objects are dealt with as part of the empirical evidence used in the course of practices of visualizing and modeling natural phenomena. This process, which can be contextualized historically in terms of the development of imaging technologies, becomes crucial in understanding what counts as empirical evidence in current scientific work.     

Exact Computation of Delaunay and Power Triangulations

In this paper we present a topologically correct and efficient version of the algorithm by Guibas and Stolfi (Algorithmica 7 (1992), pp. 381-413) for the exact computation of Delaunay and power triangulations in two dimensions. The algorithm avoids numerical errors and degeneracies caused by the accumulation of rounding errors in fixed length floating point arithmetic when constructing these triangulations.Most methods for computing Delaunay and power triangulations involve the calculation of two basic primitives: the INCIRCLE test and the CCW orientation test. Both primitives require the computation of the sign of a determinant. The key to our method is the exact computation of this sign and is based on an algorithm for determining the sign of the sum of a finite set of normalized floating point numbers of fixed mantissa length (machine numbers) exactly. The exact computation of the primitives allows the construction of the correct Delaunay and power triangulations. The method has been implemented and tested for the incremental construction of Delaunay and power triangulations. Tests have been conducted for different distributions of points for which non-exact algorithms may encounter difficulties, for example, slightly perturbed points on a grid or on a circle. Experimental results show that the performance of our implementation is comparable with that of a simple implementation of the incremental algorithm in single precision floating point arithmetic. For random distribution of points the exact algorithm is only 4 times slower than the inexact implementation. The algorithm is easy to implement, robust and portable as long as the input data to the algorithm remains exact.     

映射相关边概念的多边形内外点判别算法

提出映射相关边、密切边的概念,将点在多边形内外的判别转化为点与密切边关系的判别．通过X方向的一次映射快速求取判别点的相关边,对相关边的二次映射可得到判别点的密切边．证明了根据密切边的矢量方向就可以判别点在多边形内外．在运算效率上对射线法进行改进,当多边形的边数较多时,更能体现文中算法优越性．     

基于数学形态学的LIDAR数据分割和边缘提取

针对通过LIDAR方法获取的数据,根据矢量转化成栅格数据的方法将数据转化成图像,然后用数学形态学中的膨胀和腐蚀方法进行序贯运算.并将得到的图像进行边缘提取和边缘矢量化,得到每个地物所对应的边缘和数据点.最后通过两个算例来说明这种方法的可行性.     

Multi-label Moves for MRFs with Truncated Convex Priors

Optimization with graph cuts became very popular in recent years. While exact optimization is possible in a few cases, many useful energy functions are NP hard to optimize. One approach to approximate optimization is the so-called move making algorithms. At each iteration, a move-making algorithm makes a proposal (move) for a pixel p to either keep its old label or switch to a new label. Two move-making algorithms based on graph cuts are in wide use, namely the swap and expansion. Both of these moves are binary in nature, that is they give each pixel a choice of only two labels. An evaluation of optimization techniques shows that the expansion and swap algorithms perform very well for energies where the underlying MRF has the Potts prior. However for more general priors, the swap and expansion algorithms do not perform as well. The main contribution of this paper is to develop multi-label moves. A multi-label move, unlike expansion and swap, gives each pixel has a choice of more than two labels to switch to. In particular, we develop several multi-label moves for truncated convex priors. We evaluate our moves on image restoration, inpainting, and stereo correspondence. We get better results than expansion and swap algorithms, both in terms of the energy value and accuracy.     

复杂背景图像下基于边缘点校验的圆检测方法

针对传统圆检测方法在复杂背景下检测精度低、误识别及漏识别率高、可靠性差的缺点,提出一种适应于复杂背景图像下的圆检测方法。根据半径搜索范围,利用三级筛选法选出候选圆,对所有的候选圆统计边缘点个数,将统计结果除以半径,根据此值对候选圆进行筛选。依据统计结果对圆排序,根据设定的最小圆心距及最小半径差阈值消除因峰值扩散产生的干扰圆。实验结果表明,与传统梯度Hough变换相比,该方法的误识别率和漏识别率分别降低24%和8%,检测结果更精确,在复杂背景下的可靠性更高。     

正方棋盘中广义马步哈密顿圈问题的若干研究结果

研究了在n×n的正方形棋盘中,骑士马走非正规马步(r,s)、r≥1、s>2(或称广义马步),是否能经过棋盘中每个点一次,且仅一次又回到出发点的问题,即广义马步哈密顿圈问题.论文首先给出了已有的研究成果,然后从理论上证明了在n×n,n≤r s 1的正方形棋盘中不存在广义马步哈密顿圈.最后用实证的方法,提出了在n×n,n≥2(r s)的棋盘中存在广义马步哈密顿圈的猜想,并利用实证与链接构造法,证明了对于(r=1,s=4)的广义马步情况,当n≥10时,存在广义马步哈密顿圈.     

Edge detection with embedded confidence

Computing the weighted average of the pixel values in a window is a basic module in many computer vision operators. The process is reformulated in a linear vector space and the role of the different subspaces is emphasized. Within this framework wellknown artifacts of the gradient-based edge detectors, such as large spurious responses can be explained quantitatively. It is also shown that template matching with a template derived from the input data is meaningful since it provides an independent measure of confidence in the presence of the employed edge model. The widely used three-step edge detection procedure - gradient estimation, non-maxima suppression, hysteresis thresholding - is generalized to include the information provided by the confidence measure. The additional amount of computation is minimal and experiments with several standard test images show the ability of the new procedure to detect weak edges     

On Succinct Greedy Drawings of Plane Triangulations and 3-Connected Plane Graphs

Geometric routing by using virtual locations is an elegant way for solving network routing problems. In its simplest form, greedy routing, a message is simply forwarded to a neighbor that is closer to the destination. It has been an open conjecture whether every 3-connected plane graph has a greedy drawing in the Euclidean plane R ² (by Papadimitriou and Ratajczak in Theor. Comp. Sci. 344(1):3–14, 2005). Leighton and Moitra (Discrete Comput. Geom. 44(3):686–705, 2010) recently settled this conjecture positively. One main drawback of this approach is that the coordinates of the virtual locations require Ω(nlogn) bits to represent (the same space usage as traditional routing table approaches). This makes greedy routing infeasible in applications. In this paper, we show that the classical Schnyder drawing in R ² of plane triangulations is greedy with respect to a simple natural metric function H(u,v) over R ² that is equivalent to Euclidean metric D _E (u,v) (in the sense that $D_{E}(u,v) \leq H(u,v) \leq2\sqrt{2}D_{E}(u,v)$ ). The drawing uses two integer coordinates between 0 and 2n?5, which can be represented by logn bits. We also show that the classical Schnyder drawing in R ² of 3-connected plane graphs is weakly greedy with respect to the same metric function H(?,?). The drawing uses two integer coordinates between 0 and f (where f is the number of internal faces of G).     

再论映射相关边概念的多边形内外点判别算法

证明了文献[1](张宁宁,张树有,谭建荣.映射相关边概念的多边形内外点判别算法.计算机辅助设计与图形学学报, 2004, 16(7): 935-938)中密切边(定义3)是不正确的.在此基础上重新定义了密切边的概念,改进了文献[1]的算法,并增加了检测点在特殊位置时的判定,增强了算法的稳定性和可靠性.     

A Negotiation Meta Strategy Combining Trade-off and Concession Moves

In this paper we present a meta strategy that combines two negotiation tactics. The first one based on concessions, and the second one, a trade-off tactic. The goal of this work is to demonstrate by experimental analysis that the combination of different negotiation tactics allows agents to improve the negotiation process and as a result, to obtain more satisfactory agreements. The scenario proposed is based on two agents, a buyer and a seller, which negotiate over four issues. The paper presents the results and analysis of the meta strategy’s behaviour.     

基于顺序形态变换的图像边缘检测

该文分析了顺序形态学和普通形态学运算的特点,在此基础上研究了基于顺序形态运算的边缘检测,通过对原始图像采用不同百分位值和结构元素的顺序形态变换,可以选择不同阈值和图像中目标信号分布范围,结合Canny检测算子能有效检测灰度接近背景的目标区域的边界。