Development and evaluation of a long range image-based monitoring system for civil engineering structures

Ehrhart, Matthias; Lienhart, Werner

doi:10.1117/12.2084221

Cited by 19 publications

(17 citation statements)

References 18 publications

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“…Highly accurate data can be obtained using a telescope camera, because it uses telescope optics and magnification; however, we must also perform camera calibration, which involves the determination of intrinsic camera parameters. The intersection of the optical axis with the image sensor plane, i.e., principal point image coordinates, the focal length in the horizontal and vertical directions, and an arbitrary number of coefficients to compensate for radial and tangential lens distortions are intrinsic parameters which must be determined during camera calibration [59]. The distance between the camera center and the principal point is the focal length of pinhole cameras integrated in today's IATS.…”

Section: Iats System and Camera Calibrationmentioning

confidence: 99%

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Technological Development and Application of Photo and Video Theodolites

et al. 2021

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Theodolites are fundamental geodetic measuring instruments for all practical geodetic tasks, as well as for experimental geodetic scientific purposes. Their development has a long history. Photo and video theodolites represent the advanced development of classic theodolites. Development started in 19th century, but only in the last 15 years has commercial application been achieved in the geodetic profession. The latest development, called image-assisted total stations (IATS), is a theodolite which consists of a classic robotic total station (RTS) with integrated image sensors. It was introduced in the early 2000s. With the development of theodolites, their application became much wider; today, they can be used for structural and geo-monitoring, i.e., for the determination of static and dynamic displacements and deformations of civil engineering structures such as bridges, dams, wind turbines, and high buildings, as well as natural structures, such as mountain slopes. They can be implemented in geodetic monitoring systems, which are an integral part of engineering structural diagnosis, and they provide essential information about the current condition of the structure. This paper describes the technological development of photo and video theodolites divided into phases according to the main innovations in their development. The application of modern video theodolites (i.e., IATS) is presented through several experimental studies that were performed. The procedure of conducting measurements with this kind of instrument, as well as the analysis of acquired data and achieved results, is elaborated. Lastly, the authors conclude, according to the achieved results, that IATS can today be used for determination of quasi-static and dynamic displacements with small and high amplitudes.

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Section: Iats System and Camera Calibrationmentioning

confidence: 99%

“…The frequencies included in a time series, which can be computed via Fourier analysis, are independent of the physical unit of the time series. This is due to the linear property of the Fourier transform (Equation ( 1)), where a constant factor c may be applied before or after the transformation [59].…”

Section: Iats System and Camera Calibrationmentioning

confidence: 99%

Technological Development and Application of Photo and Video Theodolites

et al. 2021

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“…Other feature point matching methods are also validated only in short-range 185 monitoring tests (Ehrhart andLienhart, 2015a, 2015b;Khuc and Catbas, 2017b). …”

Section: Correlation-based Template Matching 139mentioning

confidence: 99%

Vision-based systems for structural deformation measurement: case studies

2018

Proceedings of the Institution of Civil Engineers - Structures

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Vision-based systems offer a promising way to measure displacement and are receiving increased attention in civil structural monitoring. However, the working performance of vision-based systems, especially their measurement accuracy and robustness to different field conditions, is not fully understood. This study reports three cases studies of vision-based monitoring tests including one in a laboratory, one on a short-span bridge and one on a long-span bridge. The tracking accuracy is quantified in laboratory conditions in the range from 0·02 to 0·20 pixel, depending on the target patterns as well as the tracking method selected. The measurement performance under several field challenges is investigated, including long-range measurement (e.g. camera-to-target distance of 710 m), low-contrast target patterns, changes of target patterns and changes in lighting conditions. Three representative tracking methods for the video processing, namely, correlation-based template matching, Lucas–Kanade optical flow estimation and scale-invariant feature transform were used for the analysis, indicating their advantages and shortcomings for field measurement. One of the main observations in field application is that changes in lighting conditions might cause some low-frequency measurement errors that could be misunderstood without prior knowledge regarding structural loading conditions.

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“…Elgemal et al [22] included computer vision in an integrated system to create a ''decision support system'' for bridges and other lifelines. It is good to note that recently several studies have been conducted to address the issue of measuring displacement of civil structures using videos cameras [23][24][25][26][27][28][29][30][31].…”

Section: Introductionmentioning

confidence: 99%

Eulerian-based virtual visual sensors to detect natural frequencies of structures

Shariati

Schumacher

Ramanna

2015

J Civil Struct Health Monit

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Natural frequency of vibration data are often used to study the behavior of structures. They are also used to calibrate finite element models and some studies have proposed that the presence and location of damage can be estimated using these data. Along this line, we earlier proposed the concept of Eulerian-based virtual visual sensors to estimate natural frequencies of structural vibrations based on the change of pixel intensity captured in a digital video. Benefits of this approach are that it allows for distributed sensing and is contactless. However, as intensity does not reflect any physical quantity, such as displacement, and the range of values is difficult to control, the signal-to-noise ratio (SNR) can be relatively low. Furthermore, impulsive changes of intensity caused by large deformations compared to the pixel size can result in an impulse train in the frequency domain which leads to ambiguity in determining peak frequencies. As a result, it is often only possible to estimate the first fundamental mode of vibration. In this paper, we present strategies using targets mounted to the structure combined with signal processing methods that significantly improve the SNR and allow for detecting higher natural frequencies of vibration. The concepts, their mathematical background, laboratory tests to prove the accuracy and enhancement of SNR, as well as an example of an in-service pedestrian bridge are presented and discussed.

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Development and evaluation of a long range image-based monitoring system for civil engineering structures

Cited by 19 publications

References 18 publications

Technological Development and Application of Photo and Video Theodolites

Technological Development and Application of Photo and Video Theodolites

Vision-based systems for structural deformation measurement: case studies

Eulerian-based virtual visual sensors to detect natural frequencies of structures

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