APPLYING 3D AFFINE TRANSFORMATION AND LEAST SQUARES MATCHING FOR AIRBORNE LASER SCANNING STRIPS ADJUSTMENT WITHOUT GNSS/IMU TRAJECTORY DATA

In this article we extend our previous work on the topic of ALS strip adjustment without GNSS/IMU trajectory data. Between overlapping strip pairs the relative orientation as a 3D affine transformation is estimated by a 3D LSM approach, which uses interpolated 2.5D grid surface models of the strips and the entire strip overlap as one big LSM window. The LSM derived relative orientations of all strip pairs in the block together with their covariance matrices are then used simultaneously as observations in an adjustment following the Gauss-Helmert model. This way the exterior orientation of each strip is computed, which refers to a relative block system. If proper ground control data is given, then an absolute orientation of the block of strips can be computed by a final LSM run. In a small example consisting of 4 strips with ca. 70% overlap the improvement in the relative geometric accuracy is demonstrated by the decreasing sigma(MAD) of the height differences from 8.4cm (before) to 1.6cm (after the strip adjustment).