High precision 2D-displacement measurement of lattice pattern using image processing

2D-displacement measurement with real time image processing is developed. The target of camera image is a lattice pattern drawn on the paper sheet. The range of measurement depends only on the size of target sheet, so that high resolution power as well as large measuring range are realized with proposal method. The histogram distribution of the image of the lattice pattern is calculated, and the position of the grid lines are detected from the peak positions of the distribution. By continuously performing this detection, it is possible to calculate the movement of the image. From the target grid lines spacing (in mm) and the grid lines spacing on the image (in pixels), the calculation of the displacement is done automatically. The features of this method are that real-time measurement can be performed with high-speed processing, measurement can be easily performed simply by setting the grid line interval (mm), and measurement can be performed with sub-pixel accuracy. In this research, the measurement accuracy and the tolerance to poor image quality of the proposed method were evaluated. As a result, it has been shown that the position of the grid line can be detected with sub-pixel accuracy even in a poor-quality image. As an application of this method, the relative displacement between the base and tested building was obtained with the measurement during 3-dimensional vibration tests.