检校场标定长焦航测相机参数
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摘要
为实现长焦航测相机内参数及畸变参数标定,提出利用室外检校场对相机进行标定的方法。介绍了该方法由初值到精确值的两步法的求解步骤、计算过程及实验过程。首先通过给定已知特征点位置信息以及不同角度不同位置下拍摄的影像,通过特征点提取及匹配,根据像点坐标与世界坐标的线性对应关系,基于直接线性变换算法建立约束方程求取相机参数初值,进而通过混合LMQN(Levenberg-Marquardt与Qusai-Newton)迭代优化加速求解精确值。与精密测角法比无需精密设备的操作及记录,只需不同位置不同姿态拍摄多张包含精确位置信息的检校场影像即可。最后进行标定实验并对结果分析,基于检校场的标定方法在参数解算中特征点最大投影误差为2.471pixel,标定参数主点精度为9.7μm(<2pixel),主距精度为4.3μm(<1pixel),解算相机拍摄位置精度0.035m,满足测绘应用的精度需求。
A two-step method was proposed to estimate parameters of long focal mapping camera by means of calibration field.The direct linear transform formulation(DLT)was used to obtain initial values for the hybrid LMQN iterative speed method by giving the feature points and the images taken from several positions and attitudes,and the whole process of calculating and experiment was described in detail.Compared with precise angle measurement method,operation and recording of accurate equipment are dispensable.It was only needed that images of calibration field with precise position information were taken from several different positions and orientations.The calibration results of experiment based on calibration field method indicate that the maximum re-projection error of fea-ture points is 2.471 pixel,the calibration accuracies of principal point and principal focal distancereach9.7μm(<2 pixel)and 4.3μm(<1 pixel),respectively,the calculated position accuracy of the camera is 0.035 m,which meets precision requirements of mapping application.
A two-step method was proposed to estimate parameters of long focal mapping camera by means of calibration field.The direct linear transform formulation(DLT)was used to obtain initial values for the hybrid LMQN iterative speed method by giving the feature points and the images taken from several positions and attitudes,and the whole process of calculating and experiment was described in detail.Compared with precise angle measurement method,operation and recording of accurate equipment are dispensable.It was only needed that images of calibration field with precise position information were taken from several different positions and orientations.The calibration results of experiment based on calibration field method indicate that the maximum re-projection error of fea-ture points is 2.471 pixel,the calibration accuracies of principal point and principal focal distancereach9.7μm(<2 pixel)and 4.3μm(<1 pixel),respectively,the calculated position accuracy of the camera is 0.035 m,which meets precision requirements of mapping application.
引文
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[3]赵振庆,叶东,张鑫,等.改进的精密测角法标定面阵摄像机参数[J].光学精密工程,2016,24(7):1592-1599.ZHAO ZH Q,YE D,ZHANG X,et al..Calibration of area-array camera parameters based on improved exact measuring angle method[J].Opt.Precision Eng.,2016,24(7):1592-1599.(in Chinese)
[4]ZHANG Z Y.A flexible new technique for camera calibration[J].IEEE Trans Pattern Analysis and Machine Intelligence,2000,22(11):1330-1334.
[5]陈刚,车仁生,叶东,等.一种基于立体模板的双目视觉传感器现场标定方法[J].光学精密工程,2004,12(6):626-631.Cheng G,CHE R SH,YE D,et al..Stereo vision sensor field calibration method based on volume template[J].Opt.Precision Eng.,2004,12(6):626-631.(in Chinese)
[6]刘伟毅,丁亚林,贾继强,等.借助于星点标定相机的内方位元素[J].光学精密工程,2010,18(9):2086-2093.LIU W Y,DING Y L,JIA J Q,et al..Calibration of inner orientation elements for camera by means of star points[J].Opt.Precision Eng.,2010,18(9):2086-2093.(in Chinese)
[7]戴东凯,王省书,胡春生,等.基于天文观测的相机标定及姿态测量技术研究[J].光学学报,2012,32(3):312005.DAI D K,WANG SH SH,HU CH SH,et al..Camera calibration and attitude measurement technology based on astronomical observation[J].Acta Optica Sinica,2012,32(3):312005.(in Chinese)
[8]周富强,邾继贵,杨学友,等.CCD摄像机快速标定技术[J].光学精密工程,2000,8(1):96-100.ZHOU F Q,ZHU J G,YANG X Y,et al..A high speed CCD camera calibration technique[J].Opt.Precision Eng.,2000,8(1):96-100.(in Chinese)
[9]杨景豪,刘巍,刘阳,等.双目立体视觉测量系统的标定[J].光学精密工程,2016,24(2):300-308.YANG J H,LIU W,LIU Y,et al..Calibration of binocular vision measurement system[J].Opt.Precision Eng.,2016,24(2):300-308.(in Chinese)
[10]孔筱芳,陈钱,顾国华,等.GPS双目摄像机标定及空间坐标重建[J].光学精密工程,2017,25(2):485-492.KONG X F,CHEN Q,GU G H,et al..GPSbased binocular camera calibration and space coordinate reconstruction[J].Opt.Precision Eng.,2017,25(2):485-492.(in Chinese)
[11]王冬,冯文灏,卢秀山,等.基于多片空间后方交会的CCD相机检校[J].测绘科学,2006,31(4):64-67.WANG D,FENG W Y,LU X SH,et al..CCD camera calibration based on space resection with multi-images[J].Science of Surveying and Mapping,2006,31(4):64-67.(in Chinese)
[12]MADSEN K,NIELSEN H B,TINGLEFF O.Methods for non-linear least squares problems[M].2nd ed.Informatics and Mathematical Modelling,Technical University of Denmark.