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A Combinatorial Bound for Beacon-based Routing in Orthogonal Polygons 正交多边形信标路由的组合界
Q4 Mathematics Pub Date : 2015-07-13 DOI: 10.20382/jocg.v13i1a2
T. Shermer
Beacon attraction is a movement system whereby a robot (modeled as a point in 2D) moves in a free space so as to always locally minimize its Euclidean distance to an activated beacon (which is also a point). This results in the robot moving directly towards the beacon when it can, and otherwise sliding along the edge of an obstacle. When a robot can reach the activated beacon by this method, we say that the beacon attracts the robot. A beacon routing from $p$ to $q$ is a sequence $b_1, b_2,$ ..., $b_{k}$ of beacons such that activating the beacons in order will attract a robot from $p$ to $b_1$ to $b_2$ ... to $b_{k}$ to $q$, where $q$ is considered to be a beacon. A routing set of beacons is a set $B$ of beacons such that any two points $p, q$ in the free space have a beacon routing with the intermediate beacons $b_1, b_2,$ ..., $b_{k}$ all chosen from $B$. Here we address the question of "how large must such a $B$ be?" in orthogonal polygons, and show that the answer is "sometimes as large as $[(n-4)/3]$, but never larger."
信标吸引是一种运动系统,机器人(建模为2D中的点)在自由空间中移动,以便始终在局部最小化其与激活信标(也是一个点)的欧氏距离。这导致机器人在可能的情况下直接向信标移动,否则会沿着障碍物的边缘滑动。当机器人可以通过这种方法到达激活的信标时,我们说信标吸引机器人。从$p$到$q$的信标路由是一个序列$b_1, b_2,$…, $b_{k}$的信标,这样按顺序激活信标将吸引机器人从$p$到$b_1$再到$b_2$…从$b_{k}$到$q$,其中$q$被认为是一个信标。信标的路由集是信标的集合$B$,使得自由空间中任意两点$p, q$具有具有中间信标$b_1, b_2,$…的信标路由。, $b_{k}$全部选自$B$。在这里,我们解决了正交多边形中“这样的$B$必须有多大?”的问题,并表明答案“有时与$[(n-4)/3]$一样大,但永远不会更大”。
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引用次数: 11
On Interference Among Moving Sensors and Related Problems 运动传感器间的干扰及相关问题研究
Q4 Mathematics Pub Date : 2015-07-08 DOI: 10.4230/LIPIcs.ESA.2016.34
J. Carufel, M. J. Katz, Matias Korman, André van Renssen, Marcel Roeloffzen, Shakhar Smorodinsky
We show that for any set of $n$ points moving along "simple" trajectories (i.e., each coordinate is described with a polynomial of bounded degree) in $Re^d$ and any parameter $2 le k le n$, one can select a fixed non-empty subset of the points of size $O(k log k)$, such that the Voronoi diagram of this subset is "balanced" at any given time (i.e., it contains $O(n/k)$ points per cell). We also show that the bound $O(k log k)$ is near optimal even for the one dimensional case in which points move linearly in time. As applications, we show that one can assign communication radii to the sensors of a network of $n$ moving sensors so that at any given time their interference is $O(sqrt{nlog n})$. We also show some results in kinetic approximate range counting and kinetic discrepancy. In order to obtain these results, we extend well-known results from $varepsilon$-net theory to kinetic environments.
我们表明,对于$Re^d$和任何参数$2 le k le n$中沿“简单”轨迹移动的任何$n$点集(即,每个坐标都用有边界度的多项式描述),可以选择大小为$O(k log k)$的点的固定非空子集,这样该子集的Voronoi图在任何给定时间都是“平衡的”(即,每个单元格包含$O(n/k)$点)。我们还表明,即使对于点在时间上线性移动的一维情况,界$O(k log k)$也是接近最优的。作为应用,我们表明可以为$n$移动传感器网络的传感器分配通信半径,以便在任何给定时间它们的干扰为$O(sqrt{nlog n})$。我们还给出了动力学近似范围计数和动力学差异的一些结果。为了得到这些结果,我们将众所周知的$varepsilon$ -net理论的结果推广到动力学环境。
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引用次数: 2
Rigid origami vertices: conditions and forcing sets 刚性折纸顶点:条件和强制集
Q4 Mathematics Pub Date : 2015-07-06 DOI: 10.20382/jocg.v7i1a9
Zachary Abel, Jason H. Cantarella, E. Demaine, D. Eppstein, Thomas C. Hull, Jason S. Ku, R. Lang, Tomohiro Tachi
We develop an intrinsic necessary and sufficient condition for single-vertex origami crease patterns to be able to fold rigidly. We classify such patterns in the case where the creases are pre-assigned to be mountains and valleys as well as in the unassigned case. We also illustrate the utility of this result by applying it to the new concept of minimal forcing sets for rigid origami models, which are the smallest collection of creases that, when folded, will force all the other creases to fold in a prescribed way.
给出了单顶点折纸折痕图能够刚性折叠的内在充要条件。我们在折痕被预先分配为山折和谷折的情况下以及在未分配的情况下对这种模式进行分类。我们还通过将其应用于刚性折纸模型的最小强制集的新概念来说明该结果的实用性,刚性折纸模型是最小的折痕集合,当折叠时,将迫使所有其他折痕以规定的方式折叠。
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引用次数: 53
Approximate Greedy Clustering and Distance Selection for Graph Metrics 图度量的近似贪婪聚类和距离选择
Q4 Mathematics Pub Date : 2015-07-06 DOI: 10.20382/jocg.v11i1a25
D. Eppstein, Sariel Har-Peled, Anastasios Sidiropoulos
$newcommand{eps}{varepsilon}$ In this paper, we consider two important problems defined on finite metric spaces, and provide efficient new algorithms and approximation schemes for these problems on inputs given as graph shortest path metrics or high-dimensional Euclidean metrics. The first of these problems is the greedy permutation (or farthest-first traversal) of a finite metric space: a permutation of the points of the space in which each point is as far as possible from all previous points. We describe randomized algorithms to find $(1+eps)$-approximate greedy permutations of any graph with $n$ vertices and $m$ edges in expected time $O(eps^{-1}(m+n)log nlog(n/eps))$, and to find $(1+eps)$-approximate greedy permutations of points in high-dimensional Euclidean spaces in expected time $O(eps^{-2} n^{1+1/(1+eps)^2 + o(1)})$. Additionally we describe a deterministic algorithm to find exact greedy permutations of any graph with $n$ vertices and treewidth $O(1)$ in worst-case time $O(n^{3/2}log^{O(1)} n)$. The second of the two problems we consider is distance selection: given $k in [ binom{n}{2} ]$, we are interested in computing the $k$th smallest distance in the given metric space. We show that for planar graph metrics one can approximate this distance, up to a constant factor, in near linear time.
$newcommand{eps}{varepsilon}$ 本文考虑了在有限度量空间上定义的两个重要问题,并在给定输入为图最短路径度量或高维欧几里得度量的情况下,对这两个问题提供了有效的新算法和近似格式。这些问题中的第一个是有限度量空间的贪婪排列(或最远优先遍历):空间中每个点尽可能远离前面所有点的点的排列。我们描述了在期望时间$O(eps^{-1}(m+n)log nlog(n/eps))$内找到任意具有$n$顶点和$m$边的图的$(1+eps)$ -近似贪婪置换的随机算法,以及在期望时间$O(eps^{-2} n^{1+1/(1+eps)^2 + o(1)})$内找到高维欧几里德空间中点的$(1+eps)$ -近似贪婪置换的随机算法。此外,我们还描述了一种确定性算法,用于在最坏情况时间$O(n^{3/2}log^{O(1)} n)$内找到具有$n$顶点和$O(1)$树宽的任意图的精确贪婪排列。我们考虑的第二个问题是距离选择:给定$k in [ binom{n}{2} ]$,我们感兴趣的是计算给定度量空间中的$k$最小距离。我们证明,对于平面图形度量,可以在接近线性的时间内近似这个距离,直到一个常数因子。
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引用次数: 9
On characterizing terrain visibility graphs 地形可视性图的表征
Q4 Mathematics Pub Date : 2015-06-02 DOI: 10.20382/jocg.v6i1a5
W. Evans, Noushin Saeedi
A terrain  is an $x$-monotone polygonal line in the $xy$-plane. Two vertices of a terrain are mutually visible if and only if there is no terrain vertex on or above the open line segment connecting them. A graph whose vertices represent terrain vertices and whose edges represent mutually visible pairs of terrain vertices is called a terrain visibility graph . We would like to find properties that are both necessary and sufficient for a graph to be a terrain visibility graph; that is, we would like to characterize terrain visibility graphs. Abello et al. [Discrete and Computational Geometry, 14(3):331--358, 1995] showed that all terrain visibility graphs are “persistent”. They showed that the visibility information of a terrain point set implies some ordering requirements on the slopes of the lines connecting pairs of points in any realization, and as a step towards showing sufficiency, they proved that for any persistent graph $M$ there is a total order on the slopes of the (pseudo) lines in a generalized configuration of points whose visibility graph is $M$. We give a much simpler proof of this result by establishing an orientation to every triple of vertices, reflecting some slope ordering requirements that are consistent with $M$ being the visibility graph, and prove that these requirements form a partial order. We give a faster algorithm to construct a total order on the slopes. Our approach attempts to clarify the implications of the graph theoretic properties on the ordering of the slopes, and may be interpreted as defining properties on an underlying oriented matroid that we show is a restricted type of $3$-signotope.
地形是在xy平面上的x单调多边形线。一个地形的两个顶点是相互可见的,当且仅当在连接它们的开放线段上或上面没有地形顶点。顶点表示地形顶点,其边表示相互可见的地形顶点对的图称为地形可见性图。我们想要找到一个图成为地形可见性图的必要和充分的属性;也就是说,我们想要描述地形可见性图。Abello等[离散与计算几何,14(3):331—358,1995]表明所有地形可见性图都是“持久的”。他们证明了地形点集的可见性信息暗示了在任何实现中连接点对的线的斜率的一些顺序要求,并且作为证明充要性的一步,他们证明了对于任意持久图$M$,在可见性图为$M$的点的广义组态中,(伪)线的斜率有一个总顺序。我们给出了一个更简单的证明,通过建立一个指向每三个顶点的方向,反映一些斜率排序要求,这些要求与$M$作为可见性图一致,并证明这些要求形成偏序。我们给出了一种更快的算法来构造斜率上的总阶。我们的方法试图澄清图论性质对斜率排序的含义,并且可以解释为定义我们所示的受限类型$3$-符号的底层定向矩阵上的性质。
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引用次数: 15
Algorithms for ball hulls and ball intersections in normed planes 规范平面上球壳和球交的算法
Q4 Mathematics Pub Date : 2015-05-21 DOI: 10.20382/jocg.v6i1a4
Pedro Martín, H. Martini
Extending results of Hershberger and Suri for the Euclidean plane, we show that ball hulls and ball intersections of sets of $n$ points in normed planes can be constructed in $O(n log n)$ time. In addition, we confirm that the 2-center problem with constrained circles for arbitrary normed planes can be solved in $O(n^2)$ time. Some ideas about the geometric structure of the ball hull in a normed plane are also presented.
推广Hershberger和Suri在欧几里得平面上的结果,证明了赋范平面上n个点集合的球壳和球交可以在O(n log n)$时间内构造。此外,我们还证实了任意赋范平面的带约束圆的二中心问题可以在$O(n^2)$时间内得到解决。本文还对球壳在规范平面上的几何结构提出了一些看法。
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引用次数: 2
The Lebesgue universal covering problem 勒贝格普遍覆盖问题
Q4 Mathematics Pub Date : 2015-02-04 DOI: 10.20382/jocg.v6i1a12
J. Baez, Karine Bagdasaryan, P. Gibbs
In 1914 Lebesgue defined a 'universal covering' to be a convex subset of the plane that contains an isometric copy of any subset of diameter 1. His challenge of finding a universal covering with the least possible area has been addressed by various mathematicians: Pal, Sprague and Hansen have each created a smaller universal covering by removing regions from those known before.  However, Hansen's last reduction was microsopic: he claimed to remove an area of $6 cdot 10^{-18}$, but we show that he actually removed an area of just $8 cdot 10^{-21}$.  In the following, with the help of Greg Egan, we find a new, smaller universal covering with area less than $0.8441153$. This reduces the area of the previous best universal covering by $2.2 cdot 10^{-5}$.
1914年,勒贝格定义了一个“泛覆盖”,它是平面的一个凸子集,它包含任何直径为1的子集的等距副本。他的挑战是用最小可能的区域找到一个通用覆盖,这已经被许多数学家解决了:Pal, Sprague和Hansen都通过从已知的区域中移除区域来创建一个更小的通用覆盖。然而,Hansen的最后一次减少是微观的:他声称删除了$6 cdot 10^{-18}$的面积,但我们表明他实际上只删除了$8 cdot 10^{-21}$的面积。下面,在Greg Egan的帮助下,我们找到了一个面积小于$0.8441153$的新的更小的泛覆盖。这将之前的最佳通用覆盖面积减少了$2.2 cdot 10^{-5}$。
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引用次数: 10
SEGMENTATION OF CYSTS IN KIDNEY AND 3-D VOLUME CALCULATION FROM CT IMAGES 肾囊肿的ct分割及三维体积计算
Q4 Mathematics Pub Date : 2015-01-31 DOI: 10.5121/IJCGA.2015.5101
Nanzhou Piao, Jong-Gun Kim, Rae-Hong Park
This paper proposes a segmentation method and a three-dimensional (3-D) volume calculation method of cysts in kidney from a number of computer tomography (CT) slice images. The input CT slice images contain both sides of kidneys. There are two segmentation steps used in the proposed method: kidney segmentation and cyst segmentation. For kidney segmentation, kidney regions are segmented from CT slice images by using a graph-cut method that is applied to the middle slice of input CT slice images. Then, the same method is used for the remaining CT slice images. In cyst segmentation, cyst regions are segmented from the kidney regions by using fuzzy C-means clustering and level-set methods that can reduce noise of non-cyst regions. For 3-D volume calculation, cyst volume calculation and 3-D volume visualization are used. In cyst volume calculation, the area of cyst in each CT slice image equals to the number of pixels in the cyst regions multiplied by spatial density of CT slice images, and then the volume of cysts is calculated by multiplying the cyst area and thickness (interval) of CT slice images. In 3-D volume visualization, a 3-D visualization technique is used to show the distribution of cysts in kidneys by using the result of cyst volume calculation. The total 3-D volume is the sum of the calculated cyst volume in each CT slice image. Experimental results show a good performance of 3-D volume calculation. The proposed cyst segmentation and 3-D volume calculation methods can provide practical supports to surgery options and medical practice to medical students.
本文提出了一种基于多张CT切片图像的肾囊肿分割方法和三维体积计算方法。输入的CT切片图像包含肾脏的两侧。在该方法中使用了两个分割步骤:肾脏分割和囊肿分割。对于肾脏分割,使用图切方法从CT切片图像中分割肾脏区域,该方法应用于输入CT切片图像的中间切片。然后,对剩余的CT切片图像使用相同的方法。在囊肿分割中,使用模糊c均值聚类和水平集方法将囊肿区域从肾脏区域中分割出来,从而降低非囊肿区域的噪声。三维体积计算采用囊肿体积计算和三维体积可视化。在计算囊肿体积时,每个CT切片图像中囊肿的面积等于囊肿区域的像素数乘以CT切片图像的空间密度,然后将囊肿面积与CT切片图像的厚度(间隔)相乘计算囊肿的体积。在三维体积可视化中,利用囊肿体积计算的结果,采用三维可视化技术来显示肾脏内囊肿的分布。三维总体积为各CT切片图像计算出的囊肿体积之和。实验结果表明,该方法具有良好的三维体积计算性能。所提出的囊肿分割和三维体积计算方法可以为医学生的手术选择和医疗实践提供实用的支持。
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引用次数: 10
TERRA FORMATION CONTROL (O R HOW TO MOVE MOUNTAINS ) 地形控制(或如何移动山脉)
Q4 Mathematics Pub Date : 2015-01-31 DOI: 10.5121/IJCGA.2015.5103
J. Rankin
The new Uplift Model of terrain generation is generalized here and provides new possibilities for terra formation control unlike previous fractal terrain generation methods. With the Uplift Model fine-grained editing is possible allowing the designer to move mountains and small hills to more suitable locations creating gaps or valleys or deep bays rather than only being able to accept the positions dictated by the algorithm itself. Coupled with this is a compressed file storage format considerably smaller in size that the traditional height field or height map storage requirements.
本文对地形生成的新隆起模型进行了推广,与以往的分形地形生成方法不同,为地形控制提供了新的可能性。有了隆起模型,细粒度的编辑是可能的,允许设计师将山脉和小山丘移动到更合适的位置,创造空隙或山谷或深海湾,而不仅仅是能够接受由算法本身决定的位置。与此相结合的是压缩文件存储格式,其大小比传统的高度字段或高度图存储要求要小得多。
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引用次数: 0
MULTIMEDIA MINING RESEARCH - AN OVERVIEW 多媒体挖掘研究综述
Q4 Mathematics Pub Date : 2015-01-31 DOI: 10.5121/IJCGA.2015.5105
S. Vijayarani, A. Sakila
Multimedia data mining is a popular research domain which helps to extract interesting knowledge from multimedia data sets such as audio, video, images, graphics, speech, text and combination of several types of data sets. Normally, multimedia data are categorized into unstructured and semi-structured data. These data are stored in multimedia databases and multimedia mining is used to find useful information from large multimedia database system by using various multimedia techniques and powerful tools. This paper provides the basic concepts of multimedia mining and its essential characteristics. Multimedia mining architectures for structured and unstructured data, research issues in multimedia mining, data mining models used for multimedia mining and applications are also discussed in this paper. It helps the researchers to get the knowledge about how to do their research in the field of multimedia mining.
多媒体数据挖掘是一个热门的研究领域,它有助于从音频、视频、图像、图形、语音、文本等多媒体数据集以及几种类型数据集的组合中提取有趣的知识。通常,多媒体数据分为非结构化数据和半结构化数据。这些数据存储在多媒体数据库中,多媒体挖掘是利用各种多媒体技术和强大的工具从大型多媒体数据库系统中寻找有用信息的一种技术。本文介绍了多媒体挖掘的基本概念及其基本特征。本文还讨论了结构化和非结构化数据的多媒体挖掘体系结构、多媒体挖掘中的研究问题、用于多媒体挖掘的数据挖掘模型及其应用。它有助于研究人员了解如何在多媒体挖掘领域进行研究。
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引用次数: 28
期刊
International Journal of Computational Geometry & Applications
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