Image rectification with the pinax camera model in underwater stereo systems with verged cameras

Vision methods are very commonly used in underwater robotics. However, the cameras must be enclosed in a sealed housing for which flat-pane windows are the most economical and hence most popular solution. But they cause non-trivial refraction-based distortions at the air-glass-water interface. Recently, a new model for underwater cameras calibration called Pinax was introduced, which combines aspects of an axial and a pinhole camera model to derive an as accurate as possible and at the same time computational feasible solution. Here it is shown, how the Pinax model can be applied to stereo cameras when two verged cameras are behind a single flat glass panel. Real world experiments under different water conditions show that our method outperforms standard methods using pinhole models in combination with in-water calibration.