Exploiting Geometric Restrictions in a PTZ Camera for Finding Point-orrespondences Between Configurations

A pan-tilt-zoom (PTZ) camera, fixed in location, may perform only rotational movements. There is a class of feature-based self-calibration approaches that exploit the restrictions on the camera motion in order to obtain accurate point-correspondences between two configurations of a PTZ camera. Most of these approaches require extensive computation and yet do not guarantee a satisfactory result. In this paper, we approach this problem from a different perspective. We exploit the geometric restrictions on the image planes, which are imposed by the motion restrictions on the camera. We present a simple method for estimating the camera focal length and finding the point-correspondences between two camera configurations. We compute pan-only, tilt-only and zoom-only correspondences and then combine the three to derive the geometrical relationship between any two camera configurations. We perform radial lens distortion estimation in order to calibrate distorted image coordinates. Our purely geometric approach does not require any intensive computations, feature tracking or training. However, our point-correspondence experiments show that, it still performs well-enough for most computer vision applications of PTZ cameras.