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H. Kager:
"The Importance of Exact Geo-referencing of Airborne LIDAR Data";
GIS@Development Asia Pacific (invited), Natural Resource Management: Going Critical (2006), Vol. 10 Issue 4; 1 - 10.

This paper deals about the importance of exact geo-referencing of airborne LIDAR data. Flying companies usually deliver their point cloud data (and even derived products as DTMs or DSMs) in a co-ordinate system specified by the client. For that purpose they use transformation elements between e.g. WGS-84 datum and the appropriate national surveying system. Nevertheless, the original navigation data (GPS, IMU) are not free from errors, esp. small systematic errors. Moreover, the calibration of the scanning system´s components is not perfect. These imperfections together yield discrepancies between overlapping laser-scanner strips which can be easily visualized by colour-coded difference-DEMs created from overlapping strips. We assume, these discrepancies are stemming from non-sufficient system calibration. They are unsatisfactory phenomena for end-users of the ground data - appearing in height as well as in ground plan.

Nevertheless, these gaps can be eliminated to a great portion doing a simultaneous 3D adjustment by least squares. An operative adjustment strategy for doing that is outlined: correcting exterior orientation elements, as well as interior orientation elements concerning the system components (misalignments, eccentricities, etc.). The method applied reminds of photogrammetric block adjustment with self-calibration.

The distribution of control-features (instead of control-points) is discussed.
Final quality checking also uses colour-coded difference-DEMs.

http://aleph.ub.tuwien.ac.at/F?base=tuw01&func=find-c&ccl_term=AC06586651

http://www.gisdevelopment.net/magazine/years/2006/april/42_1.htm