Research on 3D dimensional measurement of structures based on a dual monocular structured light system

In recent years, machine vision has been increasingly applied in automated monitoring of civil engineering. However, the rapid and accurate acquisition of displacement and shape changes of structures remains a challenge. In the use of structured light to measure medium and large-sized objects, there generally exist shadow and insufficient field of view problems, especially for the traditional monocular structured light measurement method. To solve these, this article discusses a dual monocular structured light measurement method, which projects two-way stripe structured light and performs three-step phase shift, also proposes a new phase-unwrapping method of structured light, and discusses a point filtering algorithm of fusion and stitching of the point cloud data. The phase-unwrapping method and the point filtering algorithm proposed, respectively, improves the measuring speed, especially for large-sized objects, and accuracy, compared with gray-coding method and traditional ICP (iterative closest point) method. This article performs three-dimensional measurements of ball work pieces, and the experimental results show that the fused and stitched data is significantly better than the single-field data, and the diameter error is <0.15mm for 35mm ball workpieces, and 0.32mm for 45mm ball workpieces. In addition, this article compares the experimental results with gray-coding method and traditional ICP method.