Color and depth data fusion using an RGB-D sensor for inexpensive and contactless dynamic displacement-field measurement

There are numerous applications in the field of structural dynamics that require the accurate measurement of evolving deformation fields. Although there are several sensors for direct displacement measurements at a specific point in a uniaxial direction or multicomponent deformations, there are only very limited, and relatively quite expensive, methodologies for obtaining the 3-dimensional components of a displacement of a dynamically evolving (i.e., not pseudostatically) deformation field. This paper reports the results of a comprehensive experimental study to assess the accuracy and performance of a class of inexpensive vision-based sensors (i.e., RGB-D sensors) to acquire dynamic measurements of the displacement field of a test structure. The sensor was subjected to a broad variety of different dynamic motions of varying amplitude and spectral characteristics and with varying configurations of the position and orientation of the sensor with respect to the target structure. Particular attention was devoted to quantifying the influence of various test conditions, such as amplitude, frequency, sampling rate, spatial distortion, and relationships between the RGB pixel-based measurements and the depth measurements. It is shown that the class of sensors under discussion, when operated under the performance envelope discussed in this paper, can provide, with acceptable accuracy, a very convenient and simple means of quantifying 3-dimensional displacement fields that are dynamically changing at relatively low-frequency rates typically encountered in the structural dynamics field.