Method of Space Point Positioning Based on Structure-from-Motion

In view of the difficulty of full-scale measurement of large workpieces, a portable method of space point positioning based on structure-from-motion (SfM) is proposed. First, the coded target with unique identity is pasted on the surface of the measured object to achieve the stable matching of the corresponding points of each view. Then, to avoid the cumulative error caused by the position transformation in different coordinate systems, a unified coordinate system is selected, and a reference location algorithm based on the center of barycenter constraint is proposed. On this basis, the robust estimation of the camera motion parameters is further determined, and the 3D coordinates of the mark points are reconstructed by the multi view geometric constraints, and the global optimization of the 3D reconstruction results and the intrinsic and extrinsic parameters of the camera is carried out by the beam adjustment. The experimental results show that the method can achieve high precision measurement for large workpieces. The maximum error of 3D measurement is 0.133 mm and the average error is 0.031 mm, which can meet the requirements of industrial field measurement precision for large workpieces.