Automatic tie elements detection for laser scanner strip adjustment

Measurements with airborne laser scanners are performed in strips, usually with multiple length strips and a few cross strips. Due to i) wrong or inaccurate calibration of the entire measurement system and due to ii) the limited accuracy of the exterior orientation determination with GPS and IMU and systematic errors of these devices, adjacent strips can show discrepancies in their overlap. For removing these discrepancies strip adjustment algorithms require quantification on these offsets at various locations within the overlapping zones. We present a general method for determining these discrepancies automatically based on segmentation of the overlap. A method to determine the accuracy of these discrepancy observations is demonstrated as well. In the examples we reconstruct mean offsets between neighbouring strips of a few centimetres, which, also show substantial variation along the strip axis. The accuracy of this discrepancy observations is in the order of 2cm. The method developed for discrepancy determination can be applied to height or full 3D strip adjustment. It can be used for approaches using the original measurements, the coordinates of the measured points, or only the offsets between surfaces.