【作者】 于海雁；

【导师】 乔晓林；

【作者基本信息】 哈尔滨工业大学 ， 信号与信息处理， 2007， 博士

【摘要】 在交通事故现场勘查中,应用计算机视觉测量系统通过图像之间对应点的关系可以恢复目标点的三维坐标,从而进行事故现场的事后测量和事故场景的重建。但是,大多数计算机视觉系统的三维重建只是度量重建。要想恢复出真正的欧氏重建,往往需要在现场放置尺度标杆或标定模板。而基于定焦相机构成的双目视觉系统虽然能够实现真正意义上的欧氏重建,但是由于焦距固定,使得拍摄场景范围受限。这在很大程度上降低了系统应用的灵活性,同时测量精度低或测量范围也都受到了很大的影响。针对这一问题,本文对计算机视觉的多视图三维重建技术进行了研究。通过对摄像机自标定与三维重建技术的深入研究,将传统标定技术与自标定技术相结合,应用到变焦双目系统,从而解决现有计算机视觉测量系统中的测量精度与系统应用的灵活性问题。首先,论文对固定内参数情况下的线性自标定技术进行了研究,针对现有自标定技术中绝对二次曲线的像(IAC)或二次曲线的对偶像(DIAC)矩阵必须正定这一问题,提出了新的分层自标定方法。算法利用摄像机内参数可以估计这一特点,直接对内参数矩阵进行了标定,避开了IAC或DIAC的正定问题。同时采用遗传算法进行参数求解,解决了一般算法中需要精确初值的问题。为了验证算法的性能,论文设计了大量的仿真实验和真实图像实验。实验结果表明,算法对参数标定的精度较高,在一定的噪声条件下,算法具有可行性。大多数自标定算法中只考虑了摄像机的线性投影模型,但是镜头畸变带来的图像非线性失真常常是基于图像测量中不可忽略的因素。而对于非线性模型的标定目前都是采用网格模板通过离线标定的方法。但是对于变焦系统,畸变参数随着焦距的变化而改变,这就要求我们必须采用在线标定的方法。本文针对这种情况,利用Hough变换检测直线,将直线与Canny算子检测的边缘之间存在的误差作为畸变误差,从而实现了固定内参数下的摄像机非线性投影模型的在线标定。为了获得系统应用的灵活性,本文进一步对变焦相机的自标定技术进行了研究。通过对Kruppa方程的推导,实现了两视图焦距的标定。在理论上证实了从两幅图像也可以实现焦距的标定。实验结果表明,两视图可以实现不同焦距的标定,但是其结果对噪声较为敏感,因此一般采用三幅以上视图标定摄像机焦距。在单目视觉系统研究基础上,论文对双目视觉系统的三维重建技术和自标定技术也进行了研究,并提出了将传统标定方法与自标定方法相结合的变焦双目视觉系统,即采用传统标定方法进行主点等内外参数标定,而采用自标定技术进行焦距和畸变参数标定的双目视觉系统。在此过程中,为了提高系统的标定精度,论文提出了将立体对运动前后的变换矩阵引入到匹配过程作为匹配约束的方法,提高了变换矩阵的求解精度,同时也降低了误匹配概率。这一系统有效地结合了传统标定与自标定的优点,避免了测量过程中使用标定模板的问题,在确保系统精度的前提下提高了系统应用的灵活性,为交通事故现场勘查提供了更多的方便。更多还原

【Abstract】 The computer vision measurement system can be used to investigate the traffic accident later and reconstruct the scence. The 3D structure of the objects can be recovered from the correspondences of image pairs. However, most of computer vision systems can only get metric reconstruction, and the Euclidean reconstruction is necessary for our application. So staff gauge or calibration temple are placed on locale to achieve it in these systems which will affect the accuracy and bring inconvience. And if we use stereo system with constant focal, the Euclidean reconstruct can be obtained, while the measurement scope is limited. This debases the flexibility of the system, and the measurement accuracy and scope are all affected.In this paper, the 3D reconstruction from multiple views is researched to solve this problem. Based on the researching of 3D reconstruction and self-calibration, the technique which integrates the traditional calibration and self-calibration is applied to varying focal stereo rig.Firstly, the linear self-calibration using constant intrinsic parameter is researched. A novel stratified self-calibration method is presented in this paper to solve the problem that the image of absolute conic (IAC) or dual image of absolute conic (DIAC) must be positive definite for self-calibration techniques. Because the intrinsic can be estimated, so it is possible to avoid the positive definite problem with optimizing the intrinsic parameters directly. The genetic algorithm is used to get the intrinsic parameters which need not initial values. The performance of method is confirmed by a lot of synthetic and real images. The results show that the algorithm has good accuracy and is practicable.Common self-calibration use linear camera model, but the distortion from lens can not be ignored for high accuracy measurement. The grid template is used to calibrate the linear model generally. But this method is not usable if we use vary focal system. So a calibration method on line is presented in this paper. Hough transform is used to detect lines, and canny algorithm is applied to find edges and connect edges. Therefore, the difference between the edges and lines is the distortion which can help us rectify the distort image. Because of the need of system, the self-calibration on varying focal is researched. The Kruppa equation is deduced to calibrate the focal lengths from two views. The method is verified by theory and real test result. But the method is sensitivity to image noise, so the three or more images are advised.Based on the research of single camera system, the 3D reconstruction and self-calibration of stereo rig are also studied. A stereo rig system with varying focal cameras is presented which integrates traditional calibration and self-calibration. Principal points of the cameras and other parameters are calibrated by traditional method, and only focal length and distortion parameters are calibrated by self-calibration. And the transform matrix restriction is introduced to improve on images matching during this process. This method can depress the ratio of error match and get accurate transform matrix. This system combines the advantages of traditional calibration and self-calibration method and decrease the inconvenience for using template. Good accuracy and flexibleness can be acquired for traffic accident investigation.更多还原