DISCREPANCIES BETWEEN OVERLAPPING LASER SCANNER STRIPS - SIMULTANEOUS FITTING OF AERIAL LASER SCANNER STRIPS

摘要

This paper deals about discrepancies between overlapping laser scanner strips. We assume these discrepancies stemming from non-sufficient system calibration. These discrepancies - in height as well as in planimetry - are unsatisfactory phenomena for end-users of the ground data. Nevertheless, these gaps can be eliminated to a great portion doing a simultaeous 3D adjustment by least squares An adjustment strategy is proposed for doing that: correcting those exterior orientation elements as recorded by dGPS and IMU, as well as interior orientation elements concerning the Scanner-dGPS-IMU system. The method (functional model) chosen is to apply correction polynomials in the time domain to all degrees of freedom as determined by the dGPS-IMU components and to the relative orientation parameters between those scanner-system components All these parameters may be chosen block- or strip-variant and are determined simultaneously with hybrid adjustment by least squares. "Preventive regularisation" is used to catch un-or weakly determinable parameters Automated determination (measurement) of tie features (instead of tie points) is described Since in the point-clouds no corresponding points can be found, tying features- as planes and straight lines as their intersection - are used Noise (e.g.) from the cover of vegetation has to be considered in this context, so, homologous point-clusters with low noise and few exceptions with respect to an adjusting plane have to be searched for. Speaking in the terms of standard photogrammetry, "homologous planes" replace "homologous points" as tying features in block adjustment of strips as unit; "strips" replace "photos" or "models". Nevertheless, an originally photogrammetric adjustment programme could be successfully extended to perform the task. Once, this programme had also been extended to handle scanner images, introducing time dependent parameters. The history of evolution of the mathematical model reveals the strong relationship between laser scanning and photogrammety and geodesy. The distribution of control features (instead of control points) is discussed Colour-coded difference-DEMs are used to judge the improvement of interior and exterior orientation.