Laser triangulation and photometric stereo are popular optical 3D reconstruction methods but bear limitations in underwater environment because of the refraction phenomenon. Refraction bends the usually straight rays of light to anotherdirections in the interface of a flat underwater housing. It causes the camera to capture the virtual object points instead of the real ones, so that the commonly used pinhole camera model is invalid. Therefore, in this paper, we introduce a flat refractive model for describing the geometric relation accurately between the virtual object points and the real ones, which can correct the distortions in underwater 3D reconstruction methods. The parameters of model can be estimated in a calibration step with a standard chessboard. Then the proposed geometric relation is used for rebuilding underwater three-dimensional relationship in laser triangulation and photometric stereo. The experimental results indicate the effectiveness of our methods in underwater 3D reconstruction.
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