Underwater stereo calibration utilizing virtual object points

For 3D-reconstruction of underwater scenes, a camera calibration handling refractive effects is indispensable. We present a novel geometry-based approach for calibration of stereo-camera-systems in a single underwater housing with a flat interface. Our approach consists of three steps. First, we show a hypothesis on how to relate the location of virtual object points non-ambiguously to the true object location in water. Secondly, axis determination and thirdly, distance determination of a refractive interface towards the cameras is performed with the aid of this hypothesis. We propose, that the calibration can be done with just one stereo-view of a known calibration pattern, that axis determination can be done from stereo correspondences alone and that our hypothesis is a valid constraint for stereo 3d-reconstruction. We evaluated our approach on simulated data with ground truth and real data.