A hierarchical approach for fast and robust ellipse extraction

This paper presents a hierarchical approach for fast and robust ellipse extraction from images. At the lowest level, the image is described as a set of edge pixels, from which line segments are extracted. Then, line segments that are potential candidates of elliptic arcs are linked to form arc segments according to connectivity and curvature conditions. Next, arc segments that belong to the same ellipse are grouped together. Finally, a robust statistical method, namely RANSAC, is applied to fit ellipses to groups of arc segments. Unlike Hough Transform based algorithms, this method does not need a high dimensional parameter space, and so it reduces the computation and storage requirements. Experiments on both synthetic and real images demonstrate that the proposed method has excellent performance in handling occlusion and overlapping ellipses.     

卫星编队相对动力学方程数值解法

随着卫星技术的迅速发展,编队飞行技术得到了广泛的应用,而相对动力学数学精确模型是卫星编队飞行首先要解决的问题.为了保证卫星飞行保持稳定轨道,按Hill方程的圆轨道编队设计方法应用于椭圆轨道编队设计中,分析了相对动力学方程的精确模型.在满足椭圆轨道编队周期性运动的一般性初始化条件基础上,采用椭圆轨道编队相对动力学方程中周期解的要求,提出了一种新的数值解法.通过仿真,利用STK仿真工具,得到主从卫星的相对位置变化曲线,并对误差进行了分析,进而验证了方法的有效性和可行性.     

基于改进的椭圆曲线零知识证明的智能卡系统

零知识证明已成为密码学研究者非常感兴趣的一个领域,该证明能使验证者无法得到一点知识而相信证明者确实拥有该知识。这里提出一种基于改进的椭圆曲线零知识证明的智能卡系统,该系统能够大大地提高智能卡的安全性,可以被广泛地用于金融领域。这个新方案不仅能够保证安全性,而且还减少了交互次数。同时基于椭圆曲线上的零知识证明可以用比RSA短得多的密钥,达到与RSA同等级别的安全性。     

一种基于双椭圆模型的视频人数统计方法

一种基于双椭圆模型的视频人数统计方法针对环境和背景较复杂的情况,实现了较密集人群和部分遮档的人流数统计。首先提取运动目标的外形轮廓,将外形拟合成椭圆,再根据先验知识在轮廓椭圆内拟合头部椭圆。如果外形和头部都能成功拟合成椭圆,就能简单确定出一个人体。当人群密集时,先将目标进行分割后,再进行基于双椭圆模型的目标识别。本方法适合镜头的垂直模式、倾抖模式、近景模式、远景模式,能够在鉴别人体与非人体的基础上统计人数。分别对静态图像和视频序列进行了仿真,结果表明,该方法能够准确地进行人数统计。     

Generation of anisotropic mesh by ellipse packing over an unbounded domain

With the advance of the finite element method, general fluid dynamic and traffic flow problems with arbitrary boundary definition over an unbounded domain are tackled. This paper describes an algorithm for the generation of anisotropic mesh of variable element size over an unbounded 2D domain by using the advancing front ellipse packing technique. Unlike the conventional frontal method, the procedure does not start from the object boundary but starts from a convenient point within an open domain. The sequence of construction of the packing ellipses is determined by the shortest distance from the fictitious centre in such a way that the generation front is more or less a circular loop with occasional minor concave parts due to element size variation. As soon as an ellipse is added to the generation front, finite elements are directly generated by properly connecting frontal segments with the centre of the new ellipse. Ellipses are packed closely and in contact with the existing ellipses by an iterative procedure according to the specified anisotropic metric tensor. The anisotropic meshes generated by ellipse packing can also be used through a mapping process to produce parametric surface meshes of various characteristics. The size and the orientation of the ellipses in the pack are controlled by the metric tensor as derived from the principal surface curvatures. In contrast to other mesh generation schemes, the domain boundary is not considered in the process of ellipse packing, this reduces a lot of geometrical checks for intersection between frontal segments. Five examples are given to show the effectiveness and robustness of anisotropic mesh generation and the application of ellipse packing to mesh generation over various curved surfaces.     

含埋藏椭圆型裂纹的构件脉冲放电瞬间的耦合场分析

采用数值分析的方法,对含三维埋藏椭圆型裂纹的构件放电瞬间的耦合场进行分析。计算脉冲放电瞬间椭圆形裂纹尖端附近的温度场和等效应力场的分布状态;并通过改变模型尺寸的模拟分析影响放电参数的主要因素。计算结果表明,由于电流绕流产生的焦耳热源的作用,裂纹尖端处温度瞬时急剧升高,但沿椭圆形裂纹尖端的温度值并不相同,最大值发生在长轴附近,只要放电电流的强度足够大,可以使椭圆环形裂尖均熔化形成焊口,并围绕环形裂纹尖端附近产生很大的热压应力场,可有效地遏制裂纹的扩展;在相同放电电流强度下,对椭圆裂纹尖端温度影响较大的是裂纹的绝对尺寸和椭圆长短轴的相对尺寸。在研究过程中分成热一电耦合和热一应力耦合两个过程,综合考虑材料非线性、状态变化非线性和几何非线性,结果比较符合实际。     

内槽轮和椭圆齿轮串联特性研究及其应用

探讨了内槽轮和椭圆齿轮串联时各参数变化对槽轮力学性能的影响以及在现实生产应用中各参数的选择方法,并给出了一个相应的优化实例.     

VB中任意位置椭圆的绘制

使用VisualBasic设计一个绘制椭圆的程序,利用该程序可以方便、快捷地绘制各种位置的椭圆,从而解决了VB中Circle方法不能画任意位置椭圆的问题.     

一种基于椭圆曲线可认证的电子注册方案

文章提出了一种基于椭圆曲线可认证的电子注册方案。注册码的生成与验证环节采用了椭圆曲线的思想。注册码的网上分配是基于一种椭圆曲线数字签名可认证密钥分配方案。整个过程保证了网上电子注册的安全可靠性,同时还对其安全性进行了分析。     

误差理论在快速识别椭圆和圆中的应用

本文根据数据处理领域中的误差理论提出了一种检测椭圆的新算法.它的最大特点是检测速度快、精度高,并可同时适用于圆的识别.算法在程序控制下自动给出识别结果和有关的精度评定,实验证明该算法针对实际应用中大小、方向各异的椭圆,不需要做出任何假设或附加任何条件,易于执行,实用性强.