Vision technique for deflection measurements based on laser positioning

Abstract

This paper proposes a vision-based target-free deflection measurement method of bridge. This method eliminates the trouble of installing artificial targets on the structure. The proposed method utilizes multi-point laser projection as a reference point, which can eliminate the error caused by vibration at the camera position, and also avoids the difficulty of finding the background building as a reference point. The proposed method controls the measurement accuracy by adjusting the size of the captured video area. Through the method of camera scanning, large-scale multi-point deflection measurement is carried out under the premise of certain precision. The video laser spot reference point (LSRP) before loading is selected by the image segmentation algorithm. The Oriented features from accelerated cegment Test (FAST) and rotated binary robust independent elementary features (BRIEF) (ORB) feature detection and extraction algorithm is used to detect and extract key features in the region of interest (ROI) near the LSRP. The extracted key feature points calculate the displacement of each frame of the entire video by using the Lucas-Kanade Tracking (KLT) algorithm, which ensures the maximum number of matches of key points between consecutive images. The mismatched outliers are discarded by using the Random Sampling Consistency (RANSAC) algorithm. The accuracy of the proposed method was verified by an indoor and outdoor beam experiment. In the experiment, the results obtained by the proposed method are compared with the vertical displacement values of the corresponding positions acquired by the displacement meter obtained by the high-precision DH3816N dynamic strain test system to verify the validity and accuracy of the proposed method.

Keywords:

• Bridge deflection
• target-free
• laser spot reference point
• multi-point deflection measurement
• vision-based
• image processing
• high precision

Acknowledgements

The author would like to thank the anonymous reviewers for their constructive comments, which will help improve the quality of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Supports from the National Natural Science Foundation of China (Nos. 41877251, 51708552 and 61671470), the Natural Science Foundations of Jiangsu Province (No. BK20170752), the National Key Research and Development Program of China (No. 2016YFC0802904) are gratefully acknowledged.