A method for obtaining 3-D data in alpine skiing using pan-and-tilt cameras with zoom lenses

The direct linear transformation (DLT) was applied for three-dimensional reconstruction in Alpine skiing. Because of the large field of view it is necessary to follow the skier with the cameras to receive frames with a suciently large image of the skier. In our implementation, the DLT parameters are computed for each frame of each camera separately. Consequently it is possible to rotate the cameras and to zoom the lenses. The locations of the cameras need not be known. Control points were distributed on the slope. Their coordinates were determined by geode- tic surveying. The method requires at least six control points visible in each frame. Using more than six control points reduces the reconstruction error considerably. Under optimal conditions the mean errors are less than 5 cm in each coordinate. This accuracy is sucient for inverse dynamics if the data are smoothed and the