摄像机模型的建立对于摄像机标定精度至关重要，针对该问题，对摄像机模型进行研 究，对三种畸变模型进行分析，提出了考虑径向畸变和切向畸变的摄像机非线性模型，给出了在此 非线性模型下，三维空间物点投影到二维像平面象素坐标的投影过程。同时在基于平面棋盘格的两 步标定方法的基础上提出三步标定方法。将非线性模型应用到改进的摄像机标定算法中，实验结果 表明:非线性模型下的改进标定算法具有更高的标定精度。

With consideration of the importance on camera calibration precision，camera model is studied and three types of distortion models are analyzed too. Non-linear model with radial distortion and tangential distortion is proposed. Projection course from three-dimensional point to two-dimensional image plane pixel coordinate under the non-linear model is introduced. The three-step calibration method is proposed on the basis of two-step calibration method based on checkerboard. Firstly，the area near the image center is put into compact formula in order to reduce distortion influence. Secondly，linear optimization is applied to solve distortion parameters. Thirdly， global parameters optimization with anon-linear method is finished. The non-linear model is used in the improved calibration method. The experimental results indicate that the improved calibration method under the non-linear model results in more precise calibration parameters.