An Efficient Approach for the Calibration of Multiple PTZ Cameras

Abstract

In this paper, we propose an efficient approach to infer the relative positioning and orientation among multiple pan-tilt-zoom (PTZ) cameras. In this approach, the tilt angle and altitude of each PTZ camera are estimated first based on the observation of some simple objects lying on a horizontal plane. With the estimated tilt angles and altitudes, the calibration of multiple cameras can be easily accomplished by comparing the back-projected world coordinates of some common vectors in 3-D space. This calibration method does not require particular system setup or specific calibration patterns. The sensitivity analysis with respect to parameter fluctuations and measurement errors is also discussed. Experiment results over real images have demonstrated the efficiency and feasibility of this approach. Note to Practitioners-This paper was motivated by the problem that pan-tilt-zoom (PTZ) cameras may change their poses from time to time to achieve better monitoring results. Whenever there is a change, we need to recalibrate the extrinsic parameters again. In this paper, we demonstrate a new and efficient approach to calibrate multiple PTZ cameras. The concept of our approach originated from the observation that people could usually make a rough estimate about the tilt angle of the camera simply based on some clues revealed in the captured images. Based on our approach, we can simply use some A4 papers on a table to calibrate multiple PTZ cameras. In our approach, there is no need to calculate the commonly used homography matrix. For real cases, once a set of PTZ cameras is settled, we can simply place a few simple patterns on a horizontal plane. These patterns can be A4 papers, books, boxes, etc.; and the horizontal plane can be a tabletop or the ground plane. The whole procedure does not need specially designed calibration patterns and requires only a light computational load. In the near future, we will work on the extension of the proposed approach so that we will be able to perform dynamic calibration when the PTZ cameras are under movement