On-site calibration method for an underwater stereoscopic camera system based on Scheimpflug principle

In this paper, an underwater stereoscopic camera system is modeled according to the Scheimpflug principle. A sphere target-based method is presented to determine intrinsic parameters of each camera and extrinsic parameters describing the relationship between two cameras. Relationship between projection of one sphere center on a tilted image plane and its coordinate under the camera coordinate system is given and demonstrated. When more than two sphere targets are simultaneously captured by two cameras underwater, three-dimensional coordinates of each sphere center under any one camera coordinate system can be calculated. By placing these targets at various positions, the relationship between two cameras can be determined precisely. Experimental results show that the root-mean-square error of our calibration method is about 0.017 mm. Relative error is reduced by about 55.26% compared with one classic calibration method, which proved the precision of our calibration method and descriptive model. Moreover, as the sphere is isotropy and can be located randomly, the proposed calibration method is more suitable to finish on-site calibration tasks.