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Open AccessArticle

An Improved Vision Method for Robust Monitoring of Multi-Point Dynamic Displacements with Smartphones in an Interference Environment

by 1,2,* and 1
1
School of Civil Engineering and Transportation, South China University of Technology, Guangzhou 510641, China
2
State Key Laboratory of Subtropical Building Science, South China University of Technology, Guangzhou 510641, China
*
Author to whom correspondence should be addressed.
Sensors 2020, 20(20), 5929; https://doi.org/10.3390/s20205929
Received: 4 August 2020 / Revised: 10 October 2020 / Accepted: 16 October 2020 / Published: 20 October 2020
(This article belongs to the Section Intelligent Sensors)
Current research on dynamic displacement measurement based on computer vision mostly requires professional high-speed cameras and an ideal shooting environment to ensure the performance and accuracy of the analysis. However, the high cost of the camera and strict requirements of sharp image contrast and stable environment during the shooting process limit the broad application of the technology. This paper proposes an improved vision method to implement multi-point dynamic displacement measurements with smartphones in an interference environment. A motion-enhanced spatio-temporal context (MSTC) algorithm is developed and applied together with the optical flow (OF) algorithm to realize a simultaneous tracking and dynamic displacement extraction of multiple points on a vibrating structure in the interference environment. Finally, a sine-sweep vibration experiment on a cantilever sphere model is presented to validate the feasibility of the proposed method in a wide-band frequency range. In the test, a smartphone was used to shoot the vibration process of the sine-sweep-excited sphere, and illumination change, fog interference, and camera jitter were artificially simulated to represent the interference environment. The results of the proposed method are compared to conventional displacement sensor data and current vision method results. It is demonstrated that, in an interference environment, (1) the OF method is prone to mismatch the feature points and leads to data deviated or lost; (2) the conventional STC method is sensitive to target selection and can effectively track those targets having a large proportion of pixels in the context with motion tendency similar to the target center; (3) the proposed MSTC method, however, can ease the sensitivity to target selection through in-depth processing of the information in the context and finally enhance the robustness of the target tracking. In addition, the MSTC method takes less than one second to track each target between adjacent frame images, implying a potential for online measurement. View Full-Text
Keywords: computer vision; multi-point displacement measurement; motion enhanced spatio-temporal context; optical flow computer vision; multi-point displacement measurement; motion enhanced spatio-temporal context; optical flow
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Chen, T.; Zhou, Z. An Improved Vision Method for Robust Monitoring of Multi-Point Dynamic Displacements with Smartphones in an Interference Environment. Sensors 2020, 20, 5929.

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