The comparison between the manual solution and the AAT solution for the 1:3500 images showed that (a) the RMS value of control points and the standard deviation are of the same order and (b) a lower a-posteriori value for A is observed in AAT (Table 3). The feature based matching approach provides very accurate and reliable exterior orientation parameters due to its capability of generating many redundant tie points due to the strong geometry configuration. The computational time was about 3 minutes per image and the A value was 0.30-0.35 pixel, given that the system used had four Pentium Pro 200MHz
processors, with 128MB RAM and Ultra SCSI HDD. Today on a modern system built around two Pentium IV Zeon 3.2GHz processors, with 2GB RAM the time required would be less than 1.5 minutes per image.