This paper presents a camera calibration method using circular control points whose centers need to correct bias error caused by asymmetric projection. The mathematical formulations of the correction terms are discussed. The perspective transformation matrix is first estimated using DLT (Direct Linear Transformation) method without decomposition. And then the projection of the circle is obtained directly using the elements of perspective transformation matrix. The centers of circle in the image plane are then corrected with the elements of perspective transformation matrix that will be recomputed after correction. The proposed method avoids the transformation between different coordinates. The relationships between bias error and the parameters of the circle are reported through synthetic. The real tests show that the calibration error is 0.19437 pels when the resolution of camera is 780×582 pels and the radius of circle is 20mm. The accuracy is improved after correcting asymmetric projection

and the presented algorithm is feasible and valid.