Generation of digital orthophotos from IKONOS satellite images

Due to its high spatial resolution, IKONOS imagery has the highest potential for large-scale topographic mapping of the resource satellites currently available. The orthorectification of IKONOS images thus becomes an important task. Since raw image data would, in general, not be provided by the satellite company, we have developed a method that performs the rectification of IKONOS GEO images. The proposed scheme includes the following steps: (1) the correction of relief displacement for ground control points (GCPs); (2) the performing of affine transformation between the ground coordinate system and the image coordinate system; (3) the performing of back projection for each pixel in the orthoimage; (4) the use of digital terrain model to calculate the relief displacement for the pixel in the previous step; and (5) image resampling. The experimental results indicate that the generated orthoimage may reach an accuracy of 2 m, when 6 GCPs are used.