In-flight Camera Calibration for Direct Georeferencing

Direct georeferencing is increasingly applied in connection of the photogrammetric film cameras. The prerequisite for the use of this technique is an airborne system calibration. The calibration issue was investigated by analysing 10 calibration blocks obtained with four GPS/IMU/optics-combinations. The earlier studies already showed that in-flight interior orientation determination was highly relevant with the data. The objectives of this study were to investigate the further extension of the system calibration model with the typical image deformation parameters and to evaluate efficient calibration routines for daily use. The physical image deformation parameters appeared to be quite problematic due to their high correlations with other parameters. Mathematical image deformation model of Ebner appeared to have a consistent behaviour; with the examined data the maximum corrections for image coordinates were 4-12 μm depending on the optics. It appeared that the accuracy of the direct orientation observations was the limiting quality factor. A minimal block geometry with a single bi-directional flight line and no ground control points (GCPs) allowed the determination of the principal point and boresight unknowns; the calibration with this minimal block structure was clearly advantageous. Single GCP improved the reliability, but in order to obtain good accuracy, several GCPs were needed.