Analytical Calibration of the Airborne Photogrammetric System Using A Priori Knowledge of the Exposure Station Obtained from Kinematic Global Positioning System Techniques
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Date
1991-10
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Ohio State University. Division of Geodetic Science
Abstract
The airborne photogrammetric system is a complex combination of measuring tools which form a system used predominantly in most modern mapping programs. Classic aerial photogrammetry relies on the projective transformation of known object space coordinates into the photo coordinate system, enforcing the condition of collinearity, in order to solve for the six unknown parameters of exterior orientation for each photograph. Errors due to the imperfect determination of the system calibration, particularly those errors related to the interior orientation elements of the camera lens system, propagate into the exterior orientation parameters due to the high correlation between the orientation parameters. Three of the exterior orientation parameters are the object space coordinates of the camera exposure station. In the future, the position of the exposure station will be determined by very accurate navigation systems such as the NAVSTAR Global Positioning System (GPS). Direct measurement of the exposure station position has the potential of minimizing or totally eliminating the requirement for signalized control in the object space. The positions of object space points can be extrapolated from their image coordinates through the known position of the exposure station. The extrapolation accuracy will be highly dependent on the precise calibration of the entire airborne system under normal operating conditions. Kinematic GPS techniques provide the means to accurately position the airborne system over a dense set of signalized geodetic control points so that the entire airborne can be calibrated in the environment which it normally operates. This research instrumented the calibration technique, analyzed obvious sources of systematic error, and demonstrated the technique by calibrating an airborne system. The lens system, as well as aircraft induced systematic errors, were modelled and verified. Certain systematic errors would not otherwise have been determined by normal laboratory calibrations. The airborne calibration improved the overall performance of the system. Relative positional accuracies of 5 cm were achieved for targeted object space points. These accuracies were achieved from photography obtained at an altitude of 2100 m above the ground at speeds in excess of 80 meters per second without any knowledge of the object space coordinates.