Abstract
Existing vision-based displacement sensors (VDSs) extract displacement data through changes in the movement of a target that is identified within the image using natural or artificial structure markers. A target-less vision-based displacement sensor (hereafter called “TVDS”) is proposed. It can extract displacement data without targets, which then serve as feature points in the image of the structure. The TVDS can extract and track the feature points without the target in the image through image convex hull optimization, which is done to adjust the threshold values and to optimize them so that they can have the same convex hull in every image frame and so that the center of the convex hull is the feature point. In addition, the pixel coordinates of the feature point can be converted to physical coordinates through a scaling factor map calculated based on the distance, angle, and focal length between the camera and target. The accuracy of the proposed scaling factor map was verified through an experiment in which the diameter of a circular marker was estimated. A white-noise excitation test was conducted, and the reliability of the displacement data obtained from the TVDS was analyzed by comparing the displacement data of the structure measured with a laser displacement sensor (LDS). The dynamic characteristics of the structure, such as the mode shape and natural frequency, were extracted using the obtained displacement data, and were compared with the numerical analysis results. TVDS yielded highly reliable displacement data and highly accurate dynamic characteristics, such as the natural frequency and mode shape of the structure. As the proposed TVDS can easily extract the displacement data even without artificial or natural markers, it has the advantage of extracting displacement data from any portion of the structure in the image.
Highlights
IntroductionBuilding structures are exposed to repetitive or temporary external stimuli caused by disasters such as earthquakes and winds and to usage by the occupants of the building during the life cycle
Building structures are exposed to repetitive or temporary external stimuli caused by disasters such as earthquakes and winds and to usage by the occupants of the building during the life cycle.These stimuli may cause small or large deformations of the structures
The core technologies of the target-less vision-based displacement sensor (TVDS) are the image convex hull optimization algorithm for extracting the feature points without the artificial markers attached to the structure or natural markers such as a bolt hole in the structure, and a scaling factor map that converts the pixel coordinates of the extracted feature point to physical coordinates using the external environment between the camera and the structures
Summary
Building structures are exposed to repetitive or temporary external stimuli caused by disasters such as earthquakes and winds and to usage by the occupants of the building during the life cycle. The essential aspects of the proposed TVDS is the scaling factor the method of extracting thecoordinates feature point in the imagecoordinates without targets by method using the convex map for converting the pixel to the physical and the of image extracting the hull optimization. The TVDS proposed in this study can be said to be a VDS without a target because it is a method of obtaining the displacement data by extracting the feature point from the shape of the structure without artificial or natural markers referred as the target in the digitized image. Because the basic assumption of the image convex hull optimization technique in order to extract the shape of the structure is that the structure behave the rigid body motion (see [44]), the reliability of the displacement data will be decreased by the non-rigid body motion resulted from a large deformation of the structure. The image convex hull optimization has a limitation in extracting the feature point when a large deformation occurs
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