2022 Volume 78 Issue 2 Pages I_775-I_780
This study proposes the use of image geometry transformation as a method of water surface refraction correction, which is necessary when the three-dimensional shape of underwater structures is determined using photogrammetry. Three image geometry transformations (depth-dependent affine, depth-independent affine and depth-independent perspective transforms) are proposed to transform images of underwater structures taken from a camera above water into images taken from an apparent camera position calculated by ray tracing considering refraction of light rays at the surface of the water. Accuracy verification experiments using a chessboard method showed that the depth-dependent affine and depth-independent perspective transforms were highly accurate, with u- and v-directional grid spacing errors of about 1% in the case of θ≤10°. The depth-independent perspective transformation was also found to correct trapezoidal distortions. Depth-independent perspective transformation does not require depth information and is therefore considered to be an effective refraction correction method for photogrammetric surveying of underwater structures.
