Continuous Localization and Mapping of a Pan Tilt Zoom Camera for Wide   Area Tracking
  Pan-tilt-zoom (PTZ) cameras are powerful to support object identification and recognition in far-field scenes. However, the effective use of PTZ cameras in real contexts is complicated by the fact that a continuous on-line camera calibration is needed and the absolute pan, tilt and zoom positional values provided by the camera actuators cannot be used because are not synchronized with the video stream. So, accurate calibration must be directly extracted from the visual content of the frames. Moreover, the large and abrupt scale changes, the scene background changes due to the camera operation and the need of camera motion compensation make target tracking with these cameras extremely challenging. In this paper, we present a solution that provides continuous on-line calibration of PTZ cameras which is robust to rapid camera motion, changes of the environment due to illumination or moving objects and scales beyond thousands of landmarks. The method directly derives the relationship between the position of a target in the 3D world plane and the corresponding scale and position in the 2D image, and allows real-time tracking of multiple targets with high and stable degree of accuracy even at far distances and any zooming level. 
Giuseppe Lisanti and Iacopo Masi and Federico Pernici and Alberto Del   Bimbo
cs.CV