Social infrastructures are rapidly aging, and there are concerns about the increasing cost and effort required for maintenance and management. Deflection measurement is critical in evaluating the integrity of bridges as transportation infrastructure. The sampling moiré method was developed to accurately measure the displacement of structures by capturing the regular patterns (i.e., moiré markers) attached to the structures with a digital camera. The conventional approach rigidly attaches a camera to a tripod or a fixed point. However, finding a place to photograph bridges over the sea or mountains can be challenging in real scenarios. In recent years, camera-equipped drones have rapidly become an inspection technology for bridges and other transportation infrastructure. Here, we believe drone cameras open a new door for unconstrained bridge vision inspection using the moiré phase analysis method. Therefore, we are striving to develop a novel displacement measurement method that can measure the deflection of bridges by drone aerial photography. We measured the vertical displacement of a target with a 50-mm-pitch grid pattern in the laboratory to verify its effectiveness. The newly developed measurement technology alleviates the restriction that the camera must be fixed and enables the measurement of the deflection of a more significant number of bridges under various real situations.
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