A Point Cloud Registration Method for Steel Tubular Arch Rib Segments of CFST Arch Bridges Based on Local Geometric Constraints

The multi-station registration of concrete-filled steel tubular (CFST) arch rib segments poses significant challenges due to structural complexity and environmental constraints during terrestrial laser scanning, requiring multi-angle acquisition for comprehensive coverage. This study introduces a cascaded registration framework comprising: (1) a coarse registration method utilizing local geometric features of segmented tubular joints, where equidistant cross-section partitioning extracts inherent circularity constraints from cylindrical segments, and (2) a refined registration stage employing the Coherent Point Drift (CPD) algorithm with k-d tree acceleration for computational efficiency. Experimental results demonstrate that the coarse registration achieves 31 mm RMSE with R2= 0.889, eliminating 88.9% of initial misalignment. The CPD refinement reduces RMSE to 4 mm (87% precision improvement), reaching sub-centimeter accuracy with exceptional congruence (R2 = 0.995, residual error = 0.5%). Notably, k-d tree acceleration decreases computational time by 34.2% (13.30 s vs. 20.21 s) compared to conventional CPD. Validated on 2.2 m CFST specimens, this method provides an efficient solution for multi-station point cloud registration of complex steel structures.