Ma Haichi, Ma Hongchao, Liu Ke, Luo Wenjun, Zhang Liang
School of Remote Sensing and Information Engineering, Wuhan University, Wuhan 430079, China.
Department of Oceanography, Dalhousie University, Halifax, NS B3H 4R2, Canada.
Sensors (Basel). 2020 Sep 5;20(18):5056. doi: 10.3390/s20185056.
Airborne Light Detection and Ranging (LiDAR) system and digital camera are usually integrated on a flight platform to obtain multi-source data. However, the photogrammetric system calibration is often independent of the LiDAR system and performed by the aerial triangulation method, which needs a test field with ground control points. In this paper, we present a method for the direct georeferencing of images collected by a digital camera integrated in an airborne LiDAR system by automatic boresight misalignments calibration with the auxiliary of point cloud. The method firstly uses an image matching to generate a tie point set. Space intersection is then performed to obtain the corresponding object coordinate values of the tie points, while the elevation calculated from the space intersection is replaced by the value from the LiDAR data, resulting in a new object point called Virtual Control Point (VCP). Because boresight misalignments exist, a distance between the tie point and the image point of VCP can be found by collinear equations in that image from which the tie point is selected. An iteration process is performed to minimize the distance with boresight corrections in each epoch, and it stops when the distance is smaller than a predefined threshold or the total number of epochs is reached. Two datasets from real projects were used to validate the proposed method and the experimental results show the effectiveness of the method by being evaluated both quantitatively and visually.
机载激光雷达（LiDAR）系统和数码相机通常集成在飞行平台上以获取多源数据。然而，摄影测量系统校准通常独立于LiDAR系统，且通过空中三角测量法进行，该方法需要一个带有地面控制点的测试场。在本文中，我们提出了一种通过在点云辅助下自动校准视轴偏差，对集成在机载LiDAR系统中的数码相机所采集图像进行直接地理配准的方法。该方法首先利用图像匹配生成连接点集。然后进行空间交会以获取连接点的相应物方坐标值，而由空间交会计算得到的高程则由LiDAR数据的值替代，从而得到一个新的物点，称为虚拟控制点（VCP）。由于存在视轴偏差，通过共线方程可以在选择连接点的图像中找到连接点与VCP像点之间的距离。进行迭代过程，在每个历元对视轴进行校正以使距离最小化，当距离小于预定义阈值或达到历元总数时停止。使用来自实际项目的两个数据集对所提方法进行验证，实验结果通过定量和视觉评估表明了该方法的有效性。
