基于结构光扫描的轴类锻件轴线快速提取

在基于结构光的在线测量系统中,采集到的点云数据反映了工件关键参数信息。结合轴类零件的特征,重点介绍了一种通过椭圆最小二乘拟合来提取轴线的方法,这也是后续三维重构与参数计算的基础。     

Geometric property based ellipse detection method

In this paper a simple but effective and robust ellipse detection method based on geometric property is developed, which mainly utilizes the following two aspects of ellipse geometric information:(1) Points on ellipse contour are position-symmetric and the gradient vectors of one pair of symmetric points are parallel or anti-parallel, the fact of which can be used for ellipse center location. In this part, the inner product in mathematics is introduced to evaluate the extent of parallelism of two gradient vectors, and then two concepts, inner product symmetrical energy (IPSE) and inner product consistent energy (IPCE), is defined to compute the probability of a position as a symmetric center.(2) The sum of distances of one contour point far from ellipse’s two foci is a constant. For two given positions, by computing the distribution of the sum of distances we can validate if they are the correct positions of ellipse foci. Furthermore, ellipse’s semi-major axis can be also estimated from distance distribution on the positions of ellipse foci. After determining the center, foci and semi-major axis of an ellipse candidate, other parameters can be easily deduced by resolving the elliptic equation directly.Compared with existing methods, the proposed method detects the ellipse using the geometric properties directly while avoiding the complicated application of the ellipse parameter space or fitting step, and it is simple, effective and robust. In addition, the ideas proposed in this paper can be extended for other features extraction, such as general symmetry center location and other shapes detection, and extensive experiments show the good availability of the proposed ideas.     

基于P-ECC和同余方程的分簇WSN节点身份认证机制

针对新节点加入的传感器网络中进行合法的身份认证带来的节点内存占有量大、计算量大、秘密值的信息安全度低等问题,提出一种适用于内存有限的传感网络,安全度高的节点身份认证机制。该方案采用增添节点自身密码,并采用单向哈希函数对密码和身份(ID)进行散列化,利用密码参与椭圆曲线的签名算法的生成,可信节点间采用同余方程的认证方案,且各认证阶段均采用互认证模式。该方案不仅能防范窃听、重放、注入等攻击,而且能抵御猜测攻击、中介攻击、匿名信息攻击和拒绝服务攻击。与现有算法相比,所提方案能减少节点最初内存占有量三个单位级别,减少密钥检测率。     

椭圆的线性化裁剪算法

本文基于多步法绘制理论和Brensenham算法,提出了一种新的椭圆裁剪算法。此法的主要思想是,根据给定的椭圆长短半轴参数a、b,首先在1／4椭圆弧上线性化生成两个多步数目的数组Ara[]和Arb[],然后考虑到各种裁剪需要,根据两数组的数据并结合椭圆的对称性计算出相应的椭圆裁剪数据,最后再绘出所求的裁剪图形。     

基于椭圆曲线密码体制的动态秘密共享方案

文章给出了一个基于椭圆曲线公钥密码体制的动态秘密共享方案，有效地解决了共享秘密的动态更新，子密钥动态分配和欺诈问题，且易于实现，效率高。方案的安全性基于求解有限域上椭圆曲线离散对数的困难性。     

活塞中凸形线和椭圆曲线光学测量方法的研究

分析了目前国内外对活塞测量的常用方法和不同特点,提出了光学法非接触式测量活塞中凸形线和椭圆曲线的测量原理,并给出了误差分析和实验结果。     

Projective reconstruction of ellipses from multiple images

This paper presents a new approach for reconstructing 3D ellipses (including circles) from a sequence of 2D images taken by uncalibrated cameras. Our strategy is to estimate an ellipse in 3D space by reconstructing N(≥5) 3D points (called representative points) on it, where the representative points are reconstructed by minimizing the distances from their projections to the measured 2D ellipses on different images (i.e., 2D reprojection error). This minimization problem is transformed into a sequence of minimization sub-problems that can be readily solved by an algorithm which is guaranteed to converge to a (local) minimum of the 2D reprojection error. Our method can reconstruct multiple 3D ellipses simultaneously from multiple images and it readily handles images with missing and/or partially occluded ellipses. The proposed method is evaluated using both synthetic and real data.     

智能卡中ECC抗功耗攻击方案的效率改进

研究智能卡中椭圆曲线密码(ECC)抗功耗攻击的方案,对其计算效率进行分析。根据智能卡的计算能力,比较不同坐标系中的计算代价,选用实现效率最高的坐标系组合对上述方案进行评估。在此基础上提出一种改进方案,该方案主要选取坐标系的最优组合并且将密钥分解为长度相同的多组短密钥。应用结果表明,ECC算法在智能卡中的抗攻击能力没有减弱,且执行效率提高1/4以上。     

Four-arc approximation to ellipses: The best in general

So far, the four-arc approximations to an ellipse E are made under the condition that the major and minor axes keep strictly unchanged. In general, however, this condition is unnecessary. Then the fitting can be further improved. Considering a representative quadrant of E, we first draw two auxiliary circular arcs tangent to E at the axes but having a gap ε at their boundary, such that the small arc S lies outside the large arc L. Meanwhile the extreme errors of S and L w.r.t. E are ε and −ε respectively. Giving the radii of S and L a decrement −ε/2 and an increment ε/2 brings them to join smoothly. Thus, reducing the overall error to minimum, an analytic solution in implicit form is derived.     

上海市公安局出入境管理大楼

通过对上海市公安局出入境管理大楼的设计回顾,阐述建筑师对形象的标志性、空间的流动性、功能的有序性等方面的追求,提供了一个在城市中心区处理建筑个性与城市空间协调性的案例。