| Optical measurement has been widely used in civil engineering related fields,especially in bridge inspection and monitoring due to its non-contact,high-efficiency,and rapid characteristics.Many scholars at home and abroad have already made rich research on digital image processing methods.However,the application scenarios considered by traditional optical measurement methods are often based on a fixed camera.For certain cases,camera fixation does not meet the practical needs well,leading to necessary research under this kind of occasions where camera movement needs to be considered.For example,in the deformation measurement of slender components that are often encountered in civil engineering,on the one hand,fixed cameras cause insufficient vertical resolution.,on the other hand,the site does not always provide fixed cameras a suitable position to ensure sufficient coverage of the object.In addition,in the process of using digital image methods to measure the deflection of the real bridge,the experimenters will have difficulties in the two steps of measuring target positioning and determining the scale factor due to the interference of ambient light and the limited indication performance of traditional rangefinders.Therefore,based on the digital image processing method,this article has done the following two aspects for the above-mentioned limitations in the traditional measurement method:A whole-field deformation measurement method based on homography matrix and a moving single camera is proposed.In practical applications,a single camera is held to move and shoot multiple component pictures to realize the full-field deformation measurement of slender components,which solves the problems that the camera is fixed and it is difficult to shoot the full-field and the vertical resolution is insufficient.It has the advantages of simple operation and flexible experimental layout.Among them,in order to improve the accuracy of solving the homography matrix,set the coding mark points,and optimize the RANSACK matching results based on manual screening.The reliability of the measurement method is verified in the indoor bending mechanics test of a concrete beam with a length of 6 meters.The deflection value of the key point obtained by the full-field measurement method proposed in this paper and the result of the displacement meter installed in advance are more moderately consistent.Developed a standing camera measurement system based on digital images.At present,related products have inconvenience in experimental operation,difficulty in target positioning,and difficulty in determining the scale factor.Therefore,this research has carried out an integrated design of high-performance laser pointer,rangefinder and attitude sensor in the hardware design,combined with novelty the IC-GN image processing method which has the advantages of convenient target positioning,integrated angle and distance measurement,and image acquisition.Its reliability has been verified by the positioning of the displacement stage and the measurement results of the system.Finally,based on the image measurement method,the deflection response of the Nanjing Yangtze River Bridge in daily operation is measured,and the bridge measurement effect is qualitatively measured from the practical application level.The measurement results accurately capture the changes of each key point of the bridge span when the train passes,and the changes are consistent with the laws of mechanics,thus confirming the applicability of the deflection measurement method adopted by the measurement system. |
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