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QUALITY MEASURES FOR DIGITAL TERRAIN MODELS

In the last few years a lot of new possibilities for the acquisition of terrain data were developed. Next to new developments in the area of digital photogrammetry due to automated image matching techniques, laserscanning has revolutionized the capturing of topographic data. For digital terrain models (DTMs) derived from “traditional” photogrammetric techniques accuracy measures, which were derived from theoretical but also from practical studies, are in use. With the upcoming of the new technologies the question of quality “How accurate is the DTM?” has to be studied new. This paper gives several solutions for the computation of different quality parameters. On the basis of these measures two different methods are presented. First, the empirical stochastic approach, which is mainly dependent on the point density of the data set, the root mean square error (RMS) and the local curvature of the DTM, is introduced step-by-step. Afterwards, a geometrically based approach is shown. It allows the computation of the DTM accuracy based on the local curvature of the DTM and the distance from each grid point of the DTM to the original terrain point next to it. The last quality measure helps to determine areas with unreliable surface description. The presented theories are independent from the data source, the modelling process and the software. For the verification of the theory the quality measures were practically tested with a typical airborne laserscanner data set. Additionally, the usability of the developed method was checked with photogrammetric data. A final section gives a short summary and a short outlook on future research work. * Corresponding author.