基于圆环点的亚像素摄像机自标定方法

针对现有的摄像机自标定算法抗噪声性能差等问题,分析了基于圆环点的摄像机自标定方法的原理,对现有方法作出了改进.充分利用Harris算子和Fostner算子的优点设计了一种亚像素的角点检测算法,提取的角点位置可精确到亚像素级;同时引入了等效圆心的概念,最大限度地降低了噪声干扰.然后充分利用射影几何调和共轭的理论求取摄像机的内参数.实验结果表明,该标定方法原理简单,标定结果鲁棒性较好且标定精度较高,可应用于高精度的视觉测量.     

一种基于三消隐点的摄像机自标定算法

提出了一种对摄像机进行自标定的方法.该方法是利用自然场景中三组两两正交的平行线所获得的消隐点之间具备的约束条件来实现标定的,并能够对获取的消隐点进行优化校正.利用该方法开展了实验研究,并与采用传统标定方法得到的结果进行了比较,结果表明本文所提出的算法具有较好的应用前景.     

基于等边三角形的摄像机标定方法

利用摄影儿何中交比不变性的性质,从给定的n幅图像中捉取所需要的点坐标,求解出三纽两两正交的直线的消失点的坐标.根据光心与消失点的连线为直线的方向建立3n个方程,从中线性的求解出相机的内参数.实验证明该方法不需要特定的标定模板,具有一定的实用价值.     

一种摄像机自动标定方法的设计与实现

设计并实现了一种摄像机内外参数的自动标定方法：提出了一种无伪的标定模板图像角点的自动提取,以及与对应物理空间坐标的匹配算法;进而,以此结果作为标定基础数据,采用Tsai[Tsai R Y．A versatile cameraca libration technique for high-accuracy 3D machine vision metrology using offthe-shelf TV cameras and lenses[J]．IEEE Journal of Robotics and Automation RA,1987,3(4)：323-344．]的两级标定法,获取摄像机的内外参数;以LabVIEW为平台,开发了一个摄像机自动标定系统,并进行了实验验证。     

基于辅助摄像机的机器人延伸手眼标定方法

针对机器人手臂上装载的工件等对象与摄像机之间空间关系的标定问题,本文在传统机器人手眼标定的基础上提出了机器人延伸手眼标定的概念,将机器人手眼关系拓展为延伸手眼关系.该方法通过引入辅助摄像机,利用平面标定靶标以及由机器人延伸手上的矩形特征衍生出的大量标定特征点,实现了机器人延伸手眼标定.实验结果表明,该算法可有效的解决机器人延伸手眼标定问题,标定精度取决于机器人延伸手的几何尺寸精度和获得特征点的精度,文中实验结果的RMS为0.113mm.     

一种摄像机自标定的线性方法

提出了一种基于空间共面直线从单幅图像进行摄像机自标定的线性方法.本方法结合工程应用实际,直接利用场景的直角信息,根据点的中心投影关系,推导直线的投影关系,基于平面上不平行的3条直线,由单幅图像线性的高精度的标定出摄像机内、外参数.算法用仿真实验和实拍图像都得到了精确、可靠的结果,在精度上明显优于基于共面点的算法.     

基于共面点的摄像机线性标定法

提出了一种线性求解摄像机内外参数的方法。通过分解参数确定相机主点坐标和纵横比,利用径向平行约束求解大部分的外参数,再引入新的畸变模型线性求解其余内外参数。该法特点是采用共面点标定物,且不需摄像机做任何运动就可以实现全过程的线性标定。既避免了非线性优化的繁琐和不稳定,也解决了其它线性法中部分内参数的标定问题。两套实验结果误差分别为0.3391pixels和0.6004pixels,表明该法具有较高的精度,是一种简单、有效、实用的标定法。     

回转类锻件视觉测量系统自标定

针对回转类锻件视觉测量系统标定问题,本文提出了一种基于被测对象自约束特征的系统参数自标定方法.首先,利用筒类锻件和支撑轴的回转特性,通过共轴截面曲线圆环点和极线约束建立摄像机系统内参数约束方程,求解测量系统所有内部参数.其次,在求得的内参数矩阵的基础上,通过锻件回转轴和截面图像的成像特点建立测量系统外参数方程,求解测量系统外部参数.实验结果表明,该方法只需利用被测对象自身几何约束,不需任何标定板和标定块,标定过程简单有效.     

基于双目摄像机的目标标定及校正方法研究

本文采用的是平行双目立体视觉机,主要目的是从摄像机获取的立体图像出发,根据两个摄像机之间的相对位置关系得到场景中物体的深度信息,以便实现运动人体的检测与识别。     

一种基于智能优化的摄像机标定方法研究

针对现有包装设备上对摄像机标定中传统优化算法存在的缺点,如对初始值敏感、收敛性差、易陷入局部最优解等,研究了量子粒子群优化算法在摄像机标定中的应用,提出了一种基于智能优化的摄像机标定方法,并给出了具体的步骤。实验结果表明该标定方法可以克服传统算法的不足,具有较高的精度,可以满足计算机视觉在包装工程中的应用。     

A high-accuracy monocular self-calibration method based on the essential matrix and bundle adjustment

Accurate camera calibration is necessary in photogrammetry systems. While traditional calibration methods need precise calibration pattern, this paper introduces a high-accuracy self-calibration method that doesn’t need any metric information of the scene. The proposed method combines epipolar geometry and bundle adjustment, and both intrinsic and extrinsic parameters are obtained. Synthetic data as well as real data have been used to test the method, and the simulation result shows that the mean absolute relative calibration errors of the focal lengths and the principal point are about 4.5e-4 and 8e-4, respectively, under zero-mean Gaussian noise with 0.1 pixels standard deviation. Compared with existing calibration methods, the proposed method is cost-effective and simple with comparable accuracy.     

Binocular self-calibration performed via adaptive genetic algorithm based on laser line imaging

Abstract

An accurate technique to perform binocular self-calibration by means of an adaptive genetic algorithm based on a laser line is presented. In this calibration, the genetic algorithm computes the vision parameters through simulated binary crossover (SBX). To carry it out, the genetic algorithm constructs an objective function from the binocular geometry of the laser line projection. Then, the SBX minimizes the objective function via chromosomes recombination. In this algorithm, the adaptive procedure determines the search space via line position to obtain the minimum convergence. Thus, the chromosomes of vision parameters provide the minimization. The approach of the proposed adaptive genetic algorithm is to calibrate and recalibrate the binocular setup without references and physical measurements. This procedure leads to improve the traditional genetic algorithms, which calibrate the vision parameters by means of references and an unknown search space. It is because the proposed adaptive algorithm avoids errors produced by the missing of references. Additionally, the three-dimensional vision is carried out based on the laser line position and vision parameters. The contribution of the proposed algorithm is corroborated by an evaluation of accuracy of binocular calibration, which is performed via traditional genetic algorithms.     

A proposed circle/circular arc detection method using the modified randomized hough transform

Abstract

The randomized Hough transform (RHT) is a useful tool to locate patterns in an image. In this study, we propose a modified RHT to detect circles/circular arcs efficiently. First, we segment an image into sub‐images based on edge information, then we use the proposed circular arc analysis and density check rule to modify RHT for circle/circular arc detection. In the experiments, real images are used to show the capability of the proposed method.     

Frontal gait recognition based on spatio-temporal interest points

This paper proposes a spatio-temporal interest point (STIP)-based human gait recognition method for frontal gait videos. The proposed method extracts histograms of oriented gradient (HOG) for STIPs directly from gait videos without involving a gait cycle segment, which is required by silhouette analysis as used by most gait recognition methods. Moreover, silhouette extraction may be affected by noise and carried objects leading to consequent recognition error. Matches of STIPs between two gait videos are then found in terms of HOG to measure the similarity of two videos so as to achieve the goal of gait recognition. The experimental results offer evidence that our method outperforms the existing methods on the Carnegie-Mellon University Motion of Body database and the Chinese Academy of Sciences Institute of Automation data-set B.     

一种基于截距的圆形窗口线裁剪算法

在圆形窗口圆心为坐标原点的前提下,确定两端点同时在外切正方形某边界之外或至少有一端点在圆形窗口之内的线段之后,当线段两端点都在圆形窗口之外时:如果线段所在直线在x或y任意坐标轴上截距的绝对值小于或等于圆半径r,则可快速判断线段与圆形窗口是否相交;否则,再根据点-线位置关系以及所引切线与线段分别相交外切正方形边的交点坐标相比较判断线段与圆形窗口是否相交。该方法可以加快线段与圆形窗口的求交进程,避免复杂的辅助操作,显著提高裁剪效率。     

双目视觉中距离约束的小波变换同名点匹配

针对一类特殊小波变换系数不同尺度下的过零点能提供在不同尺度下信号急速变化点的位置信息,提出了一种基于小波变换的多尺度过零点的双目立体视觉模型的同名点匹配方法,该方法采用由粗到细的匹配策略,利用转化的距离信息先匹配大尺度的小波变换系数的过零点,记录其过零点位置信息,然后应用顺序约束,即物体在左右影像点的投影顺序的一致性,匹配小尺度的小波变换系数的过零点,降低了同名点匹配搜索的复杂性,减少了误匹配,解决了同名点准确匹配难、计算量大等问题.采用该方法对篦冷机内水泥熟料高度进行测量,实验表明该方法能较精确的得出水泥熟料料层的分布状况.     

Left-handed metamaterials based on only modified circular electric resonators

Abstract

The novel design of a single-sided left-handed metamaterial (LHM) based only on modified circular electric resonators (MCERs) is presented experimentally and numerically in this letter. A capacitive gap is introduced in the middle arm of the electric resonator. Through adjusting the geometrical dimensions properly, the two frequency bands corresponding to negative permittivity and permeability overlap, which is validated by the parametric retrieval algorithm and equivalent circuit analysis. Furthermore, a dual-band LHM is achieved by combining two kinds of MCERs within the same unit cell. Compared to previous composite structures, the MCERs have the advantages of simple pattern, flexible design and fabricating three-dimensional LHMs readily.     

A diagonal-mass-matrix triangular-spectral-element method based on cubature points

The cornerstone of nodal spectral-element methods is the co-location of the interpolation and integration points, yielding a diagonal mass matrix that is efficient for time-integration. On quadrilateral elements, Legendre–Gauss–Lobatto points are both good interpolation and integration points; on triangles, analogous points have not yet been found. In this paper, a promising set of points for the triangle that were only available for polynomial degree N ≤ 5 are used. However, the derivation of these points is generalized to obtain degree N ≤ 7 points, which are referred to as cubature points because their selection is based on their integration accuracy. The diagonal-mass-matrix (DMM) triangular-spectral-element (TSE) method based on these points can be used for any set of equations and any type of domain. Because these cubature points integrate up to order 2N along the element boundaries and yield a diagonal mass matrix, they allow the triangular spectral elements to compete with quadrilateral spectral elements in terms of both accuracy and efficiency, while offering more geometric flexibility in the choice of grids. It is shown how to implement this DMM TSE for a variety of applications involving elliptic and hyperbolic equations on different domains. The DMM TSE method yields comparable accuracy to the exact integration (non-DMM) TSE method, while being far more efficient for time-dependent problems.     

A functional for shells of arbitrary geometry and a mixed finite element method for parabolic and circular cylindrical shells

In this study a higher‐order shell theory is proposed for arbitrary shell geometries which allows the cross‐section to rotate with respect to the middle surface and to warp into a non‐planar surface. This new kinematic assumption satisfies the shear‐free surface boundary condition (BC) automatically. A new internal force expression is obtained based on this kinematic assumption. A new functional for arbitrary shell geometries is obtained employing Gâteaux differential method. During this variational process the BC is constructed and introduced to the functional in a systematic way. Two different mixed elements PRSH52 and CRSH52 are derived for parabolic and circular cylindrical shells, respectively, using the new functional. The element does not suffer from shear locking. The excellent performance of the new elements is verified by applying the method to some test problems. Copyright © 2000 John Wiley & Sons, Ltd.