Method of 3D reconstruction of underwater concrete by laser line scanning

High-precision 3D (three-dimensional) reconstruction of underwater concrete is helpful for the detection and analysis of underwater concrete diseases. A prevalent method involves mounting optical cameras in waterproof housings to enable the 3D reconstruction of underwater concrete. Achieving millimetric accuracy in underwater 3D reconstruction poses a significant challenge in current research. The refraction of light on surfaces of different media and its reflection underwater complicate the process. In this paper, a 3D reconstruction method of underwater concrete based on laser line scanning is proposed. Firstly, the underwater imaging model is established by the ray tracing method, and the refraction conversion matrix is derived. Then, based on this matrix, the conversion relationship between the measured 3D size and the real 3D size of the underwater object is obtained. Finally, image restoration technology is introduced in the process of laser stripe extraction to eliminate the influence of reflected light on the extraction of laser stripe center, to improve the reconstruction accuracy. We used the independently developed laser line 3D scanning equipment to carry out experimental analysis. The results showed that the error rate caused by direct reconstruction of underwater objects was 9.75 %. Additionally, the error rate obtained from 3D reconstruction of underwater objects using the conversion model was 2.89 %. This study provides technical support for the 3D detection of underwater concrete.