Refraction correction and calibration for planar structured light system in underwater environment: an improved ray tracing method based on projection and mapping

To address the refraction-induced geometric distortion of underwater images, a simple yet effective correction method and its corresponding calibration method for a planar structured light sensor system in underwater environment are presented in this paper. The effects of various media—such as air, sealed glass, and water—on the entire system are considered in this model, along with a streamlined correction approach using an improved ray tracing method based on projection and mapping. For the distorted point cloud data obtained underwater, this method determines the refraction light path by calculating the 3D refraction spatial angles of each point, projects the light path onto a 2D plane, and combines with the 3D geometric mapping transformation to effectively restore the true spatial coordinates of the target. Underwater correction experiments were conducted using the proposed model, followed by the application of a corresponding calibration method to determine the system parameters. After calibration and correction, the 3D positioning of the corner points achieved an error of ∼0.1 mm, and the dimensional error of the corrected part of the fuel assembly was measured to be within 0.4 mm, as well as restoring geometrical integrity with 98.6% of refractive aberration elimination.