Underwater bridge pier morphology measurement method via refraction correction and multi-camera calibration

Underwater structural inspection is essential for ensuring the safety and longevity of bridges. To improve the efficiency and accuracy of these inspections, this paper presents a method for measuring the morphology of bridge piers through refraction correction and multi-camera calibration. Using an underwater visual inspection platform with appropriate lighting, the measurement equipment mitigates low visibility challenges. A coplanar camera refraction parameter calibration method based on encoded markers is proposed to reduce the effects of refraction, along with the development of a multi-refraction correction model. Additionally, a novel multi-camera extrinsic calibration method is introduced to stitch point clouds. A comparative analysis of the two extrinsic calibration methods, conducted both in air and underwater, has been performed to validate the accuracy and efficiency of the proposed approach. Finally, the circular cross-section shape of the underwater bridge pier was successfully measured, and the results of defect localization were effectively presented.