现有标定方法得到的相机参数与真实物理意义并不能精确对应，因为物理参数不能作为独立的未知数出现在方程中而是耦合在一起。当需要独立使用某参数时，必须分解投影矩阵，造成很大误差。为此提出了一种逐级标定相机各参数的方法。鉴于位姿对等效焦距敏感，基于位姿估计的变化量来标定等效焦距，然后采用平面单应提供的约束方程求解主点，用正交迭代算法来估计外参，最后计算畸变系数。实验验证了方法的正确和高精度。避免了参数之间的耦合，各参数与其物理意义相符，可独立使用。

Because physical camera parameters do not exist independently in equation but couple to each other, the camera parameters obtained by existing calibration methods do not actually match their physical meanings. Decomposing parameter directly from projection matrix can cause considerable error. To cope with this problem, a stepwise method for camera calibration is proposed. Since pose estimation is sensitive to equivalent focal length, equivalent focal length can be calibrated based on pose estimation variance; then principal point is calibrated by homographic constraint; extrinsic camera parameters are calibrated by orthogonal iteration algorithm; finally the distortion coefficients are calculated. Experiments have proved this method′s correctness and high precision, and show that this method can effectively avoid coupling of camera parameters, in which way each parameter can match its own physical meaning pretty well, and can be used independently.