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Measurement method of reference points of railway fixed pile based on monocular vision(PDF)


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Measurement method of reference points of railway fixed pile based on monocular vision
FU Qin-yi1 HU Jie-hua2
1. School of Traffic and Transportation Engineering, Central South University, Changsha 410075, Hunan, China; 2. Shenzhen TM Video Technology Co., Ltd., Shenzhen 518109, Guangdong, China
railway engineering track measurement target recognition line detection Harris corner detection Hough transformation perspective transformation
To improve the efficiency of absolute coordinates measurement of railway line fixed pile reference points, a new measurement method was proposed. The single-point measurement model of non-cooperative target was established. The laser target images were captured by monocular camera, the centroid method of saturation point was applied to exact laser spot center. The imaging rules of lines in plane were studied. A homography matrix solving method was constructed based on the orthogonal straight lines, and the image was corrected by perspective distortion. Then the horizontal and vertical offsets of laser spot and target were calculated based on the geometric similarity relationship between corrected image and target. In the indoor environment, orthogonal experiments of target image shooting were carried out. The horizontal and vertical offsets were calculated and compared. Experimental result shows that under the condition that laser spot and target are fixed, the distance from camera to target is constant, and the camera's angle is only variable, after the images are shot and corrected by perspective transformation, the errors between the horizontal and vertical offsets and the expected values are 0.082 and 0.254 mm, respectively. Under keeping the camera's angle and changing the distance from camera to target, the errors of corrected images are 0.126 and 0.014 mm, respectively. When the camera's angle and the distance from camera to target both change, the errors of corrected images are 0.329 and 0.064 mm, respectively. The errors between the horizontal and vertical offsets and the expected values of 3 tests are less than 0.5 mm. The range of horizontal and height measure errors of the system are ±1.52 and ±0.67 mm, respectively. According to the index of railway inspection tester's performance, the horizontal measure errors of railway are within ±3.0 mm and the height measure errors are within ±2.5 mm. Obviously, the precision of the measurement method can meet the railway measurement requirements. The horizontal distance measure error is totally depended on the laser range finder and tilt sensor, while the height measure error is depended on the laser range finder, tilt sensor and the offsets of laser spot to the target. 8 figs, 26 refs.


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Last Update: 2018-05-20