Accurate measurement of six Degree Of Freedom small-scale ship motion through analysis of one camera images

A new six Degree Of Freedom (6DOF) motion measurement technique for small-scale physical models of floating bodies is presented, based on analysis of image sequence from one camera. The proposed system consists of one camera and one target: the method estimates the 3-D rigid motion following the time evolution of the target of known pattern fixed to the moving body and framed by the camera. In particular, the rotation matrix and the translation vector of the 3-D rigid motion between initial still position and a generic moved position are calculated by assuming the existence of a planar homography between the camera CCD plane and the plane passing through the flat target surface. Geometrical relationship allows one the calculation of wanted 6DOFs for every point of the modeled body. In the paper, the method is mathematically presented in terms of equations of rigid motion with its associate accuracies. The image-based technique is illustrated on some tests carried out in an experimental multipurpose wave basin.

► An experimental optical tool was designed to measure the 6DOFs of a floating body in an experimental multipurpose wave basin.
► Accuracy of the proposed technique was estimated.
► Test done showed that variations in the model ship operating conditions and in the environmental forces could be ascertained using the imaging method.