To realize accurate self-calibration of pan-tilt camera with nonideal structure, an accurate pan-tilt camera model is built, and a self-calibration method for intrinsic camera parameters and pan-tilt structural parameters is proposed based on self-constraint characteristics in rotation. Firstly, according to the structural feature of the system, an accurate pan-tilt camera model, different from the ideal model, is built to describe the relative orientation and position offset among pan axes, tilt axes and the camera. Secondly, fixed entities in rotation are calculated by taking advantage of the self-constraint characteristics in rotation, and then combining with the polarizing constraint, the constraint equations of the image for an absolute conic are established and computed to obtain the intrinsic camera parameters by Cholesky's factorization. Finally, based on the intrinsic matrix of the camera, the pan-tilt structural parameters are solved by using the projection characteristics of the rotation axes and cross sections. Experimental results indicate that, for 0.5 pixel noise level, the calibration errors in focal length are less than 0.73% and in principle points are less than 0.52%, and mean error in reprojection of real images is 2.38, all of which are better than those by self-calibration method based on ideal model. The whole calibration process only utilizes the geometric constraint in active rotation of pan-tilt camera, without the information of outside scene or calibration object.
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