  Displacement is an important measurement for the assessment of structural
conditions, but its field measurement is often hindered by difficulties
associated with sensor installation and measurement accuracy. To overcome the
disadvantages of conventional displacement measurement, computer vision
(CV)-based methods have been implemented due to their remote sensing
capabilities and accuracy. This paper presents a strategy for non-target
structural displacement measurement that makes use of CV to avoid the need to
install a target on the structure while calibrating the displacement using
structured light. The proposed system called as LAVOLUTION calculates the
relative position of the camera with regard to the structure using four equally
spaced beams of structured light and obtains a scale factor to convert pixel
movement into structural displacement. A jig for the four beams of structured
light is designed and a corresponding alignment process is proposed. A method
for calculating the scale factor using the designed jig for tunable
structured-light is proposed and validated via numerical simulations and
lab-scale experiments. To confirm the feasibility of the proposed displacement
measurement process, experiments on a shaking table and a full-scale bridge are
conducted and the accuracy of the proposed method is compared with that of a
reference laser doppler vibrometer.
