Digital sampling moiré (DSM) method is a newly developed vision-based technique that uses the phase information of moiré fringes to measure movement of an object. The moiré fringes are generated from a sequence of digital images, containing a cosinusoidal grating pattern attached to the object, through down-sampling and interpolation. As the moiré fringes can magnify the pattern’s movement, this technique is expected to provide more accurate displacement measurement than the other vision based approaches. In this study, a method combining DSM with monocular videogrammetric technique is proposed to measure in-plane rotation and translation of structures. In this method, images of a two-dimensional (2D) grating pattern attached to a moving structure are acquired and decomposed into two perpendicular gratings through Fourier transform. The DSM method is used to obtain 2D phase distributions of the gratings which provide an estimation of physical coordinates for those points on the grating pattern. A previously developed monocular videogrammetric technique can then be used to obtain the rotation angle and the translation of the grating pattern. The proposed method is validated using both numerical simulation and laboratory tests.
Xinxing Chen and Chih-Chen Chang, "In-plane motion measurement by using digital sampling moiré method," Proc. SPIE 9803, Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2016, 980311 (Presented at SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring: March 22, 2016; Published: 20 April 2016); https://doi.org/10.1117/12.2217259.
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