RGB-D-DIC technique for low-cost 3D displacement fields measurements

Abstract

Optical displacement measurements can provide data on the behavior of structural elements without altering key parameters such as damping, stiffness, and mass. Optical techniques can also substantially simplify the equipment that is required for acquiring data effectively and can map displacements at specified locations of elements with complex geometries, such as steel connections. In addition, these techniques can provide simultaneous data at multiple points using a single imaging device (for plane measurements) or multiple devices (for three-dimensional measurements); however, these systems rely on specialized imaging sensors that are coupled with expensive optics and high-cost software licenses. In contrast, range/depth cameras (RGB-D) can provide a color and 3D imaging solution for capturing motion at an affordable cost. These cameras are widely available and applied in the video game industry using a mass production scheme; hence, they are of low cost. This paper proposes a methodology, along with an experimental validation, of a large three-dimensional displacement field measurement approach that uses artificial vision techniques. This methodology uses digital image correlation (DIC) principles and an RGB-D camera (RGB-D-DIC) for a variety of structural applications, which range from experimental modal analysis, cyclic loading tests, and creep tests to static displacement tests. A low-cost Kinect V2 camera was single- and stereo-calibrated, evaluated and implemented in a comparison test with a commercial three-dimensional DIC system. With the RGB-D camera, the proposed methodology can provide accurate displacement measurements that are comparable to those that are obtained via precise displacement measurement techniques and/or by using sensors; further, this methodology has the advantages of low cost, ease of implementation, and contactless measurement and provides three-dimensional information.