Method for extrinsic parameters calibration of Pan-Tilt camera using intersecting lines from two images

Abstract

Pan-Tilt (PT) cameras are widely used in video surveillance because of larger field of view. The camera’s intrinsic parameters remain unchanged and the extrinsic parameters calibration of the PT camera should be addressed when it comes to visual geometric measurement. In this paper, the unknown parameters of the PT camera are only reduced to the rotation angles in horizontal and vertical directions, and a method for extrinsic parameters calibration using intersecting lines from two images is presented. An improved feature point matching algorithm is proposed to obtain the natural feature point pairs between images acquired before and after rotation, and direct linear transformation method is employed to obtain the rough rotation angles by using the natural feature point pairs. Based on rotation constraint, the optimization function established by the projections of the intersections of the straight lines in natural scene is then used to calculate the refined extrinsic parameters. Computer simulations and real experiments prove the effectiveness of the improved feature point matching algorithm and the proposed calibration method. Experimental data reflects the extrinsic parameters estimated by our method are close to reference values from high-precision stepper motors, and the average deviation of Euler angles representing rotation matrix and translations from our method relative to reference values does not exceed 0.03° and 0.27 mm, respectively.