ICGCM Papers:
Ground Control Monitoring Systems and Practices
 
 
A Practical Application of Photogrammetry to Performing Rib Characterization Measurements in An Underground Coal Mine Using a DSLR Camera
35th International Conference on Ground Control in Mining
A Practical Application of Photogrammetry to Performing Rib Characterization Measurements in An Underground Coal Mine Using a DSLR Camera
by
Brent A SlakerKhaled M Mohamed, NIOSH, Office of Mine Safety and Health Research, Pittsburgh, United States
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[Conference] 35th International Conference on Ground Control in Mining
[Price] Free  [Comments] 0
[Topical Area] Ground Control Monitoring Systems and Practices
[Author] Brent A SlakerKhaled M Mohamed, NIOSH, Office of Mine Safety and Health Research, Pittsburgh, United States
[Abstract] 
Key Conclusions:
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Using a non-metric camera, a successful photogrammetry survey will prioritize sufficient feature overlap with changing camera locations, then lighting conditions, and lastly optimized camera settings. An organized and methodical approach to photogrammetry eliminates common mistakes and significantly reduces processing time.
Key Findings:
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Several experiments showed that the lighting method did not matter significantly, assuming the scene was sufficiently and appropriately illuminated allowing features to be distinguished. The distance to the subject only serves to increase the potential resolution of the reconstruction, which has a minimal impact on result accuracy at DSLR pixel densities and in coal mine geometries. It was found, however, that an increasing resolution was preferable when measuring plane orientations, but a high point cloud density would likely be excessive otherwise. F-stop changes do affect the depth of field, and were found to significantly affect image quality in situations where multiple angles are necessary to establish cleat orientations. Photograph overlap is very important to proper reconstruction, and at least 70% overlap between photograph pairs is ideal to avoid unnecessary post-processing.
Objective of the Paper:
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To test the practical use of photogrammetry in underground coal using a non-metric camera, several experiments were performed at the NIOSH Safety Research Coal Mine using different lighting conditions, distance to subject, camera settings, and photograph overlap. The suggestions and guidelines proposed are designed to increase the quality of photogrammetry inputs and outputs as well as minimize processing time, and serve as a starting point for an underground coal photogrammetry study.
Problem Statement:
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Due to the variability in underground opening geometries and ground behavior, point measurements often fail to capture the true behavior of mine workings. Photogrammetry is a potential fast, cheap, and precise alternative to extensometers, tape measures, or lasers, but its application in underground coal has been limited.