Multi-unit global-local registration for 3D bent tube based on implicit structural feature compatibility

Point cloud registration for evaluating the shape of 3D bent tubes is a preferred method for improving the forming quality and reducing fabrication costs. In this process, large nonlinear deformations, smooth regions, and low overlap result in massive outliers, making accurate registration for forming iterative optimization a challenging yet indispensable technique. We propose a new registration method based on implicit structural feature compatibility to predict the global-local rigid transform for multi-unit 3D bent tubes, called ISFC. In the two-stage tactic of ISFC for the alignment of the cross-source point cloud, the rigid compatibility in overlap regions and non-rigid compatibility in deformation regions are discriminated by the soft-distance consistency metric for global correspondence initialization. A new implicit axial structure constraint is established by evolution from the surface point to the interior based on the grassfire analogy, which joins faithful anchor points to generate a robust global correspondence hypothesis. Based on the global pose transformation, an innovative multipliers method named PC-ADMM is proposed for sequential local registration, which introduces a processing constraint into the optimization objective of the Lie group to refine tube unit transformation. The robustness and accuracy of the proposed method are confirmed by extensive registration experiments on synthetic and real-world tube datasets.