PHOTOGRAMMETRIC EVALUATION PROCEDURES FOR PANNABLE AND TILTABLE CAMERAS OF VARlABLE FOCAL LENGTH

  • Volker DRENK

Abstract

Institut fur Angewandte Trainingswissenschaft Leipzig, Germany To obtain detailed pictures when recording spacious athletic movements it is desirable to follow the athlete's movements with the available cameras and to zoom cameras so as to have close-up shots. Very often, it is only this way that analyses of competitions become possible and sensible at all. Appropriate photogrammetric evaluation procedures need to be developed for the panning, tilting, and zooming of cameras when recording. The development of a procedure is based on the assumption that the camera orientation in an initial position is known, and that for rotating, cameras are attached to a tripod. Changes in orientation may then be functionally described in terms of the geometrical conditions when the camera turns around the panning axis and the tilting axis which turns along. When the situation of the axes of rotation, the angles of rotation, and the change in focal length are known, the camera orientation of the initial position may be transformed into the one of the actual picture. The parameters bf transformation may be calculated using the information provided by control points in the recordings. Since functional relationships are non-linear, and, normally, measuring information available exceeds the number of wanted parameters, this is done by calculus of observations. Two control points will do to obtain the panning and tilting angles and change in focal Length. Beyond the usual comparisons with control points, additional model data was used to validate the correctness of algorithmic and numeric solutions and program technology. These investigations considerably extend the range of procedures to treat pannable and tiltable cameras of variable focal length so far available. The procedures that had been developed so far started from simplified models rather than from a general perspective as shown here. The described procedures have proved particularly successful when we applied them to evaluate jumps in track & field and figure skating training and competitions. Moreover, other users have already used them for movement analysis.