Implementation&Engineering Applications Of Image-based Dynamic Displacement Monitoring System

Image processing has a more extensive range of application with the rapid development of computer. Real-time image acquisition and processing can solve many engineering problems. The deflection is one of the key parameters that reflect the bridge health status, deflection measurement is essential in the monitoring of bridge parameters. There are a lot of deflection measurement methods in engineering community, but most of them have shortcomings such as the slow acquisition speed, poor real-time, computer interface inconvenient, so they are often subject to considerable restrictions in practical engineering applications.This subject applies some of the image processing algorithms to actual projects and designs a system to dynamically monitor the deflection of large-bridge. This system consists of an industrial CCD, a telephoto lens, two LED lights and a set of software based on Visual C++platform. Principles of the system are as follows, fix and install two LED lights in the test point of structure. LED lights will produce a shift with the test point. Fix the CCD and telephoto lens in a position where can observe the LED lights in the horizontal direction. High-speed collects digital images of the test site using CCD, at the same time compute the two-dimensional displacement of the spots in the image; get the actual two-dimensional displacement of the test points by converting. Demarcate the transformation parameter of actual distance and pixel distance using two LED lights. We can use the displacement of an LED light or the average displacement of the two LED lights as the displacement of the test points.Image processing algorithms this system used includes:(1)Image threshold segmentation. Gray collected color images, binary the image using the threshold segmentation method this paper proposed for spot images and then split out the location of the spot region.(2)When marking conversion parameters and measuring displacement with two LED lights, calculate the center of gravity coordinates of the two spot using region growing algorithm.(3)When measuring displacement with one LED lights, calculate the center of gravity coordinates of the single spot using center of gravity method.(4)Marquee measuring. Select a part containing the spot with a rectangular box to calculate, without calculating all the pixels of the image, in order to shorten the processing time of an image and improve the real-time performance of the system.When the system was completed, it was tested in laboratory and some actual bridges. Test results show that this system is convenience to be used, has a high measurement accuracy, low cost, broad application prospects and development space. The system applies not only to bridge deflection detection, but also to any large-scale structure displacement measurement.