Geometric Potential of IKONOS- and QuickBird-Images

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 rigorous mathematical model. Rational polynomial functions for the ground coordinates in relation to image coordinates should not be determined directly based on control points, this will hide discrepancies at the control points and do not guarantee a sufficient geometric quality 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 some problems of the IKONOS images with the information about the view direction which is included also in the rational functions distributed by SpaceImaging. 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). DEMs also can be generated by automatic image matching of IKONOS and QuickBird Images. Stereo pairs taken from the same orbit do not cause any problem with the generation of DEM’s; this is different for images taken with a larger time interval from different orbits. The change of the vegetation, but also the change of the length of shadows and other radiometric differences may lead to problems with the automatic image matching.