Accuracy Assessment of Commercial Self- Calibrating Bundle Adjustment Routines Applied to Archival Aerial Photography

The use of archival or historical photography for photogrammetric purposes often involves a lack of data concerning the aerial cameras employed, difficulties in identifying control points on the photos and inappropriate conservation of the photography. When camera calibration parameters are unknown, they should be estimated by means of a self-calibrating bundle adjustment. Several calibration models available in the Leica Photogrammetry Suite software have been tested on two archival datasets, captured in 1956 and 1977, covering the same working area. The accuracy of the dataset triangulation was found to depend significantly on the self-calibration method and the number of ground control points used; when the latter ranged from six to nine per stereopair, self-calibrating bundle adjustment techniques were found to slightly, but not always significantly, improve the photogrammetric capability of archival aerial photography. Thus, the adoption of selfcalibration cannot guarantee the improvement of results when working on poorly conserved imagery. Results from such datasets are very dependent on numerous local variables which cannot be extrapolated to other areas for the same camera since each dataset is unique and may present systematic errors of a different nature.