Application of Airborne Laser Scanning-based Technology for Bridge Geometric Alignment Measurement

To address the low efficiency, long operation time, and limitations of high-altitude measurements associated with traditional total station methods in main cable profile measurement and cable clamp positioning of suspension bridges, this study proposes an airborne LiDAR-based measurement approach. A UAV equipped with a Global Positioning System/Inertial Navigation System (GPS/INS) is employed to acquire full-bridge three-dimensional point cloud data. By incorporating geometric constraints, automatic segmentation of key components, including main cables, cable clamps, and hangers, is achieved. Subsequently, edge detection and geometric fitting methods are applied to extract critical parameters such as the main cable profile and clamp inclination angles. Field validation is conducted on the Nanjing Xianxin Road Yangtze River Crossing, and the results are compared with those obtained from total station measurements. The results indicate that the maximum error in clamp inclination is 0.2°, with an average error of 0.11°, both of which are within the specification limit of 0.5°. In addition, the fitted main cable profile shows excellent agreement with the design profile. Moreover, the proposed method enables rapid acquisition of complete and continuous bridge data, significantly improving measurement efficiency. The findings demonstrate that airborne LiDAR technology can achieve high-precision, non-contact measurement of key geometric parameters during suspension bridge construction, exhibiting strong practical applicability and potential for engineering implementation.