射电望远镜主反射面的浮动式视觉测量技术研究

The large radio telescopes need to realize real-time and high precision measurement in a few minutes, but none of the total station, the laser tracker, the monocular or binocular vision can meet this requirement. Floating binocular vision measurement system includes two floating workbenches, and each workbench is fixed with a target measurement camera and an attitude measurement camera. The intersection measure of two target measurement cameras guarantees the precision of view field by limiting the single field of view in a small scale. Meanwhile, the two workbenches drive the target measurement cameras to move and obtain different intersection areas, so the measurement range can be expanded. Firstly, based on the camera self-calibration technology in computer vision, we use uncontrolled points to calibrate the initial values of the cameras’ intrinsic parameters and the normalized extrinsic parameters. Then, we resolve the real translation parameters by a distance constraint, because through self-calibration we got that the translation parameters are normalized. Finally, bundle adjustment is applied to get the final values of the intrinsic and extrinsic parameters. This calibration method improves the precision and robustness, meets the requirement of the measurement. Furthermore, the structure of floating cameras reduces the requirement for equipments. We use each attitude measurement camera to detect the target attitudes, and convert them into the corresponding attitude of the intersection measurement camera in the same workbench. The relative position of the two attitude measurement cameras can be got by the on-line field calibration. This system doesn’t need global control points; the measurement error is equivalent to single measurement error, thus the accumulate errors can be avoided while expanding the measurement range.

大型射电天文望远镜，要在数分钟内对主反射面面型进行实时动态、高精度测量，全站仪、激光跟踪仪、单目或固定式双目，难以满足要求。浮动式双目视觉测量系统有两个浮动工作台，每个工作台上固结目标测量相机和姿态测量相机。两个工作台的目标测量相机进行交会测量，单视场限制在较小范围内，保证单视场精度；工作台带动两台目标测量相机指向不同交会区域，拓展测量范围。由计算机视觉中摄像机自标定技术，用非控制点，标定得到内参数和归一化外参数的初值；用一个距离约束对外参数平移量解归一化；用光束平差方法，算出内外参数终值；这种内外参数标定方法，可以提高标定精度和鲁棒性，满足现场测量需要。两个交会测量相机的姿态是浮动的，降低对现场支撑的要求；姿态测量相机检测姿态靶、换算得到同一工作台上的交会测量相机姿态；两个分立姿态靶的相对位置由现场标定得到。系统不需要全局控制点；测量范围拓展时，测量误差相当于单次误差、不会累积。

在大空间范围内坐标测量的要求中，例如FAST射电望远镜主反射面面型检测的场合，传统的测量方法，如全站仪、激光跟踪仪等，难以满足测量精度和测量速度的要求，为此，我们研究满足这一测量要求的视觉测量方法。.移动式的单相机测量方法难以满足测量速度的要求，固定式双目视觉测量方法的测量范围有限。为此，我们研究浮动式视觉测量方法中的关键问题，摄像机内参数的标定，摄像机外参数的检测等。.研究了摄像机自标定技术，采用非控制点就可以实现对摄像机内参数的高精度标定，可以满足对摄像机内参数的现场实时标定的要求。建立了浮动式双目视觉测量的系统模型；不依赖于全局坐标系，用两个分立式的姿态靶标，标定同一工作台上目标测量相机和姿态测量相机的空间姿态变换矩阵。.该测量系统不需要辅助的精密装置，即浮动工作台不需要提供精密的旋转量和平移量，测量过程中需要的所有量都是通过图像测量的方式进行量测。.因为两个测量单元是分别安装在各自的测站工作台上，且两个测站工作台都具有6个自由度，可以很方便的通过调节工作台来测量不同的区域。特别对于不同测量区域间可以不包含重合区域也可以进行测量。.不论测量哪个待测的小目标区域，所重构的标识点的坐标都是建立在基准靶坐标系下，所以对不同的小测量区域的测量结果不需要再进行统一坐标系转化，故在拓展测量区域的过程中，不会有累积误差产生。.在实际测试中，进行10组测试，摄像机焦距(4672像素)的标准差小于0.04像素，摄像机主点(1024像素)的标准差小于0.005像素，两个摄像机之间姿态变换矩阵中三个欧拉角的标准差为6角秒、2角秒、5角秒。