Assessment of the Accuracy of Close Distance Photogrammetric JRC Data
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Poropat, George
Gratchev, Ivan
Balasubramaniam, Arumugam
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Abstract
By using close range photogrammetry, this article investigates the accuracy of the photogrammetric estimation of rock joint roughness coefficients (JRC), a measure of the degree of roughness of rock joint surfaces. This methodology has proven to be convenient both in laboratory and in site conditions. However, the accuracy and precision of roughness profiles obtained from photogrammetric 3D images have not been properly established due to the variances caused by factors such as measurement errors and systematic errors in photogrammetry. In this study, the influences of camera-to-object distance, focal length and profile orientation on the accuracy of JRC values are investigated using several photogrammetry field surveys. Directional photogrammetric JRC data are compared with data derived from the measured profiles, so as to determine their accuracy. The extent of the accuracy of JRC values was examined based on the error models which were previously developed from laboratory tests and revised for better estimation in this study. The results show that high-resolution 3D images (point interval ≤1 mm) can reduce the JRC errors obtained from field photogrammetric surveys. Using the high-resolution images, the photogrammetric JRC values in the range of high oblique camera angles are highly consistent with the revised error models. Therefore, the analysis indicates that the revised error models facilitate the verification of the accuracy of photogrammetric JRC values.
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Rock Mechanics and Rock Engineering
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© 2016 Springer-Verlag Wien. This is an electronic version of an article published in Rock Mechanics and Rock Engineering, 2016, Volume 49, Issue 11, pp 4285–4301. Rock Mechanics and Rock Engineering is available online at: http://link.springer.com/ with the open URL of your article.
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Civil engineering
Civil geotechnical engineering
Resources engineering and extractive metallurgy