. The images were orthorectified using Leica Photogrammetric Suite 9.0 (LPS) (Leica Geosystems Geospatial Imaging, LLC). Ground coordinates of 32 ground control points (GCPs) were acquired with a Trimble Pro XR GPS unit and differentially corrected. During image processing, we noticed that the image center coordinates recorded during flight did not coincide with the visually estimated image center coordinates, as estimated from a QuickBird satellite image. For the eight images, the average difference between GPS-recorded and visually estimated image centers was
31.02 m +/- 6.9 m. At the small footprint size of those images, this discrepancy represents 16% of image width and
22% of image height. We found that using the GPS-acquired image center coordinate represented too large of an error for processing in the LPS software and resulted in an inability of the software to acquire automatic tie points or solve the aero triangulation. For that reason, we visually estimated the image center coordinates by comparison with a QuickBird image.