Correction of the Asymmetrical Circular Projection in DLT Camera Calibration

The objective of camera calibration is to establish the relationship between 3D world coordinates and their corresponding 2D image coordinates. There are various kinds of control points used in the calibration procedure. However, many of them are too sensitive to the thresholding error. Circular control points do not have this problem but they need to be corrected the distortion caused by the asymmetric perspective projection. In this paper, we present a camera calibration method using circular control points. The perspective transformation matrix is first estimated using DLT method. The centers of circle in the image plane are then corrected with the elements of perspective transformation matrix that will be recomputed after correction. After several iterations the remaining error will be small. The mathematical formulations of the correction terms are discussed. Real data has been used to test the proposed technique. The results indicate that the error component of calibration is reduced compared with uncorrected points.