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Camera distortion correction method based on cross ration invariance

In order to avoid falling into the local optimal solution in the process of linear optimization, a calibration method for calculating the radial and tangential distortion coefficients is proposed. Firstly, the initial internal and external parameters of the camera are obtained by using the coordinates of the characteristic points in the central region of the calibration image. Camera imaging procedure is dividedinto two separate steps in which ideal image point is moved to actual image point through radial distortion and tangential distortion in sequence. With the distortion model and crossratio invariance, the distortion coefficient of the camera can be solved.. It is assumed that the point after distortion correction conforms to perspective projection principle, and the exact value is approximated step with the distortion model and iteration. Compared with the traditional nonlinear optimization method, the average back-projection error of the corrected image coordinates is significantly reduced and has better robustness and accuracy.