Easy Calibration for Para-catadioptric-like Camera

For omnidirectional cameras, most of the previous calibration methods from lines use conic fitting. This paper presents a calibration method for para-catadioptric-like cameras from lines without conic fitting under a single view. We establish equations on the five camera intrinsic parameters. These equations are linear for the focal lengths and skew factor once the principal point is known. The principal point can be approximated well by the center of the imaged mirror contour in practice or can be accurately estimated by quadric equations. After obtaining the principal point, we propose an algorithm to calibrate the focal lengths and skew factor. The algorithm needs neither prior structure knowledge nor conic fitting and is linear, which make it easy to implement. Other omnidirectional cameras can also use this presented work if high accuracy is not required. Experiments demonstrate the efficiency of the proposed algorithm.