Accurate 3-D Shape Measurement for Large Objects Using Speckle-Assisted Fringe Projection and Global Markers Localization

Digital fringe projection (DFP) three-dimensional (3-D) shape measurement technique has been extensively researched and applied due to its advantages of high accuracy and high efficiency. To retain the measurement accuracy for large objects, results of multiple measurements are required to be aligned based on the combination of DFP and auxiliary positioning instruments, which decreases the measurement efficiency and limits the practical application. This article presents an accurate and efficient scheme for large-scale 3-D shape measurement based on speckle-assisted fringe projection and global markers localization. Taking advantage of the triple-view geometric constraints and stereo structured-light (SL) model, arbitrary 3-D surface can be reconstructed with high quality by projecting only four patterns. To align multiple local shape data of large objects without using auxiliary positioning instruments, an accurate data registration method based on global markers reconstruction and localization is presented, which first calculates the 3-D coordinates of all noncoded markers pasted on the object surface by sequential matching, incremental markers reconstruction, and global optimization based on bundle adjustment followed by multiple local data registration through local-to-global iterative closest point (ICP) matching. The experimental results indicate that the proposed method can substantially decrease the accumulated measurement error and achieve commensurate accuracy with the auxiliary positioning methods.