Test and Calibration of a DTP Scanner for GIS Data Acquisition

Abstract

DTP scanners have undergone rapid developments the last few years and have characteristics that make them attractive for use in photogrammetric, cartographic and GIS applications, as for example for scanning of aerial and satellite film imagery, plans and small format maps. This data or other derived products like DTMs and digital orthoimages are important data layers in GIS. However, the DTP scanners also have some deficiencies like format limited in most cases to A3 or A4, a geometric resolution that in best case is 1200 dpi and most importantly exhibit geometric inaccuracies that usually exceed 0.1 mm. While the first two deficiencies can be corrected only by the scanner manufacturers, the last one maybe accounted for by calibration procedures that can be applied by the user. An improvement of the geometric accuracy of DTP scanners by calibration would make their use possible in much more applications. In this paper test patterns and a method for the geometric calibration of the Agfa Horizon DTP scanner are presented. The method, at least conceptually, is applicable to other scanners with similar characteristics. First results show a reduction of the geometric errors after calibration to 7 μm in CCD-line direction and 15 μm in scanning direction.