The introduction of active (pan-tilt-zoom or PTZ) cameras in Smart Rooms in addition to fixed static cameras
allows to improve resolution in volumetric reconstruction, adding the capability to track smaller objects with
higher precision in actual 3D world coordinates. To accomplish this goal, precise camera calibration data
should be available for any pan, tilt, and zoom settings of each PTZ camera. The PTZ calibration method proposed
in this paper introduces a novel solution to the problem of computing extrinsic and intrinsic parameters
for active cameras. We first determine the rotation center of the camera expressed under an arbitrary world
coordinate origin. Then, we obtain an equation relating any rotation of the camera with the movement of the
principal point to define extrinsic parameters for any value of pan and tilt. Once this position is determined,
we compute how intrinsic parameters change as a function of zoom. We validate our method by evaluating the
re-projection error and its stability for points inside and outside the calibration set.Postprint (published version