基于Halcon的单目相机标定方法与测量实验

机器视觉已经在现代工业自动化生产中得到了广泛应用,尤其是在三维测量领域。物体三维空间与二维图像间的关系求解离不开相机标定,尤其是相机标定结果的优劣直接决定了机器视觉的测量精度。通过搭建单目相机视觉系统实验平台,先分析了相机标定的工作原理,再利用Halcon软件的标定助手功能对型号为GB050-2-7×7的圆点标定板进行相机标定,获得了相机的内参和外参。在进一步测量实验中验证了单个特征圆点测量偏差为0.03862 mm、多个特征圆点测量平均偏差为0.05655 mm,二者测量精度都高于0.1 mm,说明了利用机器视觉进行测量能够满足常用精度需求。     

宽覆盖面阵CCD测绘相机标定方法

本文首先对宽覆盖面阵测绘相机的组成和工作原理进行介绍.针对这种相机的特殊性,提出了对相机内方位元素的标定方法.通过对所研制相机参数的测量,利用偏最小二乘回归理论方法标定出了相机的内方位元素.并通过对标定结果的分析,验证了标定方法的正确性以及精度的可靠性.     

一种星球漫游车的增强环境地形重构

本文提出一种基于相机自标定和准稠密匹配相结合的星球漫游车的环境地形重构方法,通过SIFT特征点提取,Kruppa方程的相机自标定、准稠密匹配以及三维重构,生成漫游区域的环境地形图. 与传统方法相比,该方法首先通过Kruppa方程可以不依赖星球地形地貌场景的几何结构实现车载相机参数的自标定,解决车载相机参数不一致性问题;其次,通过基于SIFT特征点的准稠密匹配能够快速获得更多可靠而准确的匹配点;最后,利用相机参数标定结果和匹配点实现稠密的、高精度的星球漫游车环境地形重构.实验结果证明了该方法的有效性.     

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。     

多场景下基于快速相机标定的柱面图像拼接方法

针对目前利用相机标定参数进行图像拼接的方法存在受场景限制大、标定过程复杂而耗时长的问题,提出一种多场景下基于快速相机标定的柱面图像拼接方法。首先,利用棋盘格标定板角点特征提取精度高的特点,使其分别位于两两邻接图像的重叠视场中,对该图像序列依次进行角点提取、精确化和匹配等预处理,以准确快速求解出待拼接图像间的配准参数;然后利用标定得到的配准参数快速拼接图像,通过柱面投影以保持图像的视觉一致性,并采用多频段融合以保留图像的细节信息;最后,将整个系统搭建在低功耗嵌入式平台,实现可在多场景下完成快速标定及基于标定参数的拼接过程。实验结果表明,该文方法在室内及隧道等场景下可准确快速完成相机标定,图像拼接过程耗时短,同时可保证较高的拼接精度和较好的成像效果,具有较强的鲁棒性。     

遗传算法在双激光雷达位姿标定中的应用

本文针对双激光雷达相对位姿标定的问题,提出了一种基于遗传算法优化的标定算法。本文首先介绍了基于激光雷达定位的移动机器人定位系统,说明了激光雷达定位的具体原理及步骤,提出双激光雷达定位的必要性。然后建立标定模型,构建参数的成本方程,利用最小二乘法初步求解出标定参数后,又提出了新的优化目标方程,同时引入遗传算法实现了3个自由度的同时优化,包括1个旋转自由度和2个平移自由度。整个优化过程中,详细介绍了遗传算法的优化流程及相关参数的选取,最后通过实验对比验证,表明优化算法的有效性。     

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.     

数字近景摄影测量中相机内参数校准

以数字近景摄影测量中相机内参数为研究对象,分析了相机成像模型和镜头畸变模型,使用基于平面标定物的方法对内参数进行了校准。根据数字近景摄影系统的特点和用途,设计和制作了具有多种特征的标定板,给出了相机内参数校准的步骤。对角点检测函数做了算法上的分析,编写了适合标定板的角点检测函数。用该方法对数字近景摄影相机的内参数进行了校准试验,角点检测的平均误差＜0.02 pixel。     

Catheter localization using C-arm with flat-panel

比较了影像增强器型C臂和平板C臂这两种C臂系统在空间定位上的优劣势,在此基础上设计了一种针对平板C臂的定位方法,该方法借助相机的针孔模型标定C臂系统成像模型,应用三角测量原理进行空间点的定位.利用自行设计的标定模板进行了单、双平板C臂的标定及立体定位试验.试验结果表明,双平板C臂的定位精度高于单平板C臂,两者定位的最大误差均小于1.25mm,平均误差小于0.62mm,均能满足临床应用需要.该方法具有原理简单、易实现的优点,由于成像原理的一致性,对不同厂家生产的平板C臂具有通用性.     

一种面结构光投影仪的标定方法

目的 研究并提出一种简单的面结构光投影仪的标定方法,结合试验搭建的测量平台,实现对饮料瓶、易拉罐、瓶盖等形状规则的包装件以及轮廓复杂人脸的准确测量。方法 首先借助二维灰度棋盘格标定板并采用张正友法标定好摄像机,再向标定板投影设定好的黑白棋盘格图案,然后结合图像阈值分割和形态学操作方法获取相机捕获投影图案的特征点坐标,最后使用标定好的摄像机参数来标定投影仪。结果 文中提出的标定方式相对操作简单、成本低,且在x和y方向的重投影误差基本都小于1个像素。结论 测量实验结果表明,文中标定方法能保证对人脸模型较理想的测量精度,有较好的应用范围。     

Stereo calibration of binocular ultra-wide angle long-wave infrared camera based on an equivalent small field of view camera

ABSTRACT

In this paper, a stereo calibration method for binocular ultra-wide angle long-wave infrared camera is proposed on the basis of an equivalent small field of view camera. Extrinsic parameters are calibrated through the corrected images from the left and right cameras. They can be viewed as images taken by a small field of view camera. The calibration procedure consists of three steps: monocular calibration, distortion correction and extrinsic parameters calibration. In order to evaluate the accuracy of the method, stereo vision of the camera is modelled and a 3D reconstruction approach is presented. A series of experiments, including intrinsic parameters, extrinsic parameters and 3D reconstruction, are conducted to validate the proposed method. The results show that the baseline length error decreases to 0.67%, and the relative error for the 3D reconstruction of corners is smaller than 8.11%. In contrast to the common stereo calibration method, it improves calibration accuracy.     

一种立体视觉测量高精度标定新方法

提出一种实现通用摄像机标定和现场高精度立体视觉传感器标定的新方法。该方法无需预先给定初始参数,而是根据投影矩阵计算摄像机参数的初始值,结合镜头畸变的标定数学模型,实现通用摄像机标定;在立体视觉传感器三维测量模型基础上,引入目标距离约束建立结构参数标定优化目标函数,从而得到使空间距离偏差最小的最优结构参数,实现传感器现场高精度标定。实验结果表明,上述方法标定精度较高,已标定传感器空间距离测量相对误差小于0.45%。     

Novel method of calibration with restrictive constraints for stereo-vision system

Regarding the calibration of a stereo vision measurement system, this paper puts forward a new bundle adjustment algorithm based on the stereo vision camera calibration method. Multiple-view geometric constraints and a bundle adjustment algorithm are used to optimize the inner and outer parameters of the camera accurately. A fixed relative constraint relationship between cameras is introduced. We have improved the normal equation construction process of the traditional bundle adjustment method, so that each iteration process occurs just outside the parameters of two images that are taken by a camera that has been optimized to better integrate two cameras bound together as one camera. The relationship between the fixed relative constraints can effectively increase the number of superfluous observations of the adjustment system and optimize higher accuracy while reducing the dimension of the normal matrix; it means that each iteration will reduce the time required. Simulation and actual experimental results show the superior performance of the proposed approach in terms of robustness and accuracy, and our approach also can be extended to stereo-vision system with more than two cameras.     

Static error budget analysis for a land-based dual-camera mobile mapping system

A mobile mapping system (MMS) is developed based on a direct sensor orientation technique that integrates GPS/inertial measurement unit (IMU) and digital cameras. This system is capable of directly mapping geospatial information without the requirement of ground control. In this article, an MMS composed of two digital single-lens reflex cameras and an Applanix POS AV-510^© is described. There are several systematic errors that need to be calibrated before achieving the goal of direct georeferencing. These are related to lens distortion, the lever-arm between the GPS and the camera's perspective center, and the boresight misalignment angles between the IMU and the camera frame. Experimental results show that the calibration field is the major error source. However, with the designed system, we can achieve a maximum three-dimensional positioning error of less than 18.27 and 7.74?cm at distances 20?m using a single camera with parallel imaging and dual-cameras with convergent imaging, respectively. The results demonstrate that the potential of high-accuracy land-based MMS applications is promising.     

基于标准球的显微图像测量系统标定方法

提出一种利用标准球对显微图像测量系统进行标定的方法．该方法利用显微系统小视场小景深的成像特点简化计算模型,减少标定参数．通过标准球图像在水平和垂直方向上的直径比计算比例因子;利用标准球边缘图像的边缘点集．运用优化的方法来计算成像系统的畸变系数和主点位置．系统的放大倍数由标准球的实际直径来标定得出．利用标准球在多摄像机公共视场内其轮廓在任何位置均可见这一特性,可同时对显微图像测量系统中的多个摄像机进行标定,简化标定过程．实验结果表明,该方法标定精度较高,标定后的测量系统的极限误差3σ为2．4μm．     

A two-point spatial mapping method for hybrid vision systems

We propose a new spatial mapping method for hybrid vision systems consisting of an omnidirectional camera and an active perspective camera. We calculate the relative position between the optical centers of the two cameras based on pre-acquisition parameters of two sample points from the observed scene, avoiding the difficulty and error in direct measurement, and at the same time using fewer points. We derive the formula of the relative position between the omnidirectional camera’s optical center and the active camera’s optical center from the distance between two points, and give a method for calculating the corresponding pan and tilt angles of the active camera from the coordinates in the omnidirectional image. Simulation and real experiments show that the two-point spatial mapping method has higher estimation accuracy than the homography calibration method, and at the same time has higher consistency among test points.     

An improved two-point calibration method for stereo vision with rotating cameras in large FOV

At present, binocular stereo vision is gradually being applied for 3D coordinate measurements in large fields of view (FOVs). In this study, a binocular stereo vision system with fixed and non-zooming cameras in a large FOV is constructed, in which cameras can rotate horizontally and vertically. All intrinsic parameters except the focal length of the cameras are set to default values and these focal lengths are calibrated offline in advance. Only the pitch angle and yaw angle of each camera need to be obtained during rotation. Therefore, we present a novel calibration method by using two control points and transform the imaging model of the pitch and yaw angles into a quadratic equation of the tangent value of the pitch angle so that the closed-form solutions of the pitch and yaw angles can be obtained. Computer simulation and real experiments demonstrate the effectiveness of the proposed method.     

基于视觉标定的包装搬运机器人定位方法

目的为了提高包装搬运机器人的定位精度,提出一种基于机器视觉的末端执行器定位方法。方法基于OpenCV设计一种视觉标定算法,该算法包括摄像机标定和位姿标定,可实现待码放物体图像坐标和机械手坐标之间的变换。结合工控机和运动控制卡设计其控制系统,同时给出硬件设计和软件设计方法。最后进行实验研究,包括原点定位和重复定位。结果实验结果表明,所述控制方法能够提高搬运机器人的定位精度,原点定位误差约为0.14 mm,重复定位误差约为0.6 mm。结论该搬运机器人定位方法能够满足包装码垛要求。     

用三线法标定车载摄像机的外部参数

根据摄像机透视投影原理,三条互不重合的平行线在图像平面上具有相同的消失点和不同的斜率。按照针孔成像模型,经过数学推导可以建立摄像机的外部参数与消失点和成像斜率之间的解析表达式,无需经过迭代和优化计算。实现过程只需要地面上有三条平行线,然后通过手工或自动的方式确定出这三条直线成像的交点和斜率,就可以标定出摄像机的外部参数。实验表明,该方法可以在不同环境下进行车载摄像机标定,方位角和俯仰角的标定误差小于百分之一弧度。     

The effects of a camera's intrinsic parameters on the determination of a coordinate frame

Abstract

In this paper, two methods, the Individual Calibration Method (ICM) and the Simultaneous Calibration Method (SCM), are used to calibrate a vision system with two cameras. The first approach calibrates a camera individually. For the second approach, two or more sets of camera intrinsic and extrinsic parameters are determined simultaneously such that the position errors for the 3‐D points are minimized. We show, theoretically and experimentally, the following results: (a) the offsets of the image centers do not affect significantly the position and orientation of a coordinate frame with respect to a stereo vision system with two cameras; (b) the lens distortion will not change dramatically the position and orientation of a coordinate frame with respect to a stereo vision system. We also find that (a) there is a difference in the determination of an object's location for the simultaneous and individual calibration methods; (b) the approach of calibrating two cameras simultaneously has the advantage of better accuracy over the method of individual calibration.