In-Plane Movement Measurement Technique Using Digital Sampling Moire Method

Digital sampling moire (DSM) method is a vision-based technique that uses phase differences of the moire fringes to measure two-dimensional (2D) translations. However, it assumes no in-plane rotation is present, and its accuracy would be affected if rotation is involved with translation. To decompose translation and rotation, we propose an enhanced DSM (EDSM) method in this study. First, the EDSM method used the derivatives of phase values to calculate the in-plane rotation angle, and then employed the 2D rigid transformation algorithm to compute the translation. We performed laboratory tests to compare the proposed EDSM method with the DSM method and the photogrammetric method using the Harris corner detector. The results revealed that the EDSM method outperforms the DSM method when rotation is applied in the motion, and the EDSM method is more robust to the image scaling factor compared with the photogrammetric method. To verify its applicability, we then applied the EDSM method to track displacements of a steel beam and a bamboo bridge. This study provides an accurate and robust method for structures' in-plane motion measurement. (c) 2019 American Society of Civil Engineers.