Camera Calibration Using Multiple Sheets Planar Pattern

Camera calibration is a necessary step in 3D vision measurement. Classic technique uses a volume calibration pattern with control points distributing in a 3D space, which is expensive to be made and difficult to be used everywhere. Zhang proposed a planar pattern based calibration method, making the calibration process accessed to almost everyone. Nowadays, consume camera with zoom lens is populated and always used for measurement. Such a camera has the advantage to zoom the lens to get a maximum resolution images for objects with different sizes at an adequate distance. The size of Zhang's planar pattern is fixed, not suitable for a zoom lens. In this paper, a multiple sheets planar pattern is used to deal with this situation. The calibration pattern is made of 1-4 sheets of planar pattern distinguished with coded markers, and the total size. can be modified by changing the distance between the planar sheets or the number of sheets to suit for different lens setting. Such composed calibration pattern is easy used both for laboratory and industrial situation. In the calibration process, one sheet of the planar pattern is first used to get an initial calibration according Zhang's method, and also the initial coordinates of all the control points in the sheets of planar patterns. Then a bundle adjustment algorithm is carried out incorporating of the planar constraints and distance constraints in the planar patterns to obtain a set of precision parameters. Some examples are presented to show the effeteness of the method.