Orthoimages and DEMs by QuickBird and IKONOS

摘要

The very high resolution space images from IKONOS and QuickBird are today in a competition to aerial images. The resolution is sufficient for the generation of Orthoimages at a scale of approximately 1:8000 up to 1:5000. Also the geometric potential is satisfying, but it is necessary to use a strict geometric model. Rational functions for the relation of the image to the ground coordinates should not be determined directly based on control points, because this will hide discrepancies at the control points and do not guarantee the correct geometry for areas with poor control point distribution. The geometric models used for CARTERRA Geo-images (IKONOS) and QuickBird Basic Imagery are explained together with the existing problems, especially the problems of the IKONOS images with the information about the view direction which is included also in the rational functions. The mayor geometric limitation for the production of Orthoimages is not the stable geometry of the space images; it is caused by the used existing digital elevation models (DEMs) from the national mapping agencies or from published DEMs like the GTOPO30 or based on SRTM. DEMs also can be generated by automatic image matching of IKONOS and QuickBird Images. Stereo pairs taken in the same orbit do not cause any problem with the generation of DEM's; this is different if images taken with a larger time interval from different orbits shall be handled. The change of the vegetation, but also the change of the length of shadows and other radiometric differences can lead to problems with the image matching.