3D rock slope data acquisition by photogrammetry approach and extraction of geological planes using FACET plugin in CloudCompare

Structure from motion (SfM) permits a fast and inexpensive way to obtain data necessary for geotechnical characterization of rock slope. Unlike scanline survey, a traditional technique, SfM can reduce the risk, time, cost, bias in measurement and improve the accessibility, quantity and quality of data collection. A small and low cost Unmanned Aerial Vehicle (UAV), DJI Phantom 4 Pro mounted with 20 megapixels camera is utilized to capture high quality images in this study with Real-Time Kinematic Global Positioning System (RTK-GPS) being used to obtain coordinates of 10 Ground Control Points (GCP) distributed evenly on the rock slope. Images registered and aligned with GCP render better accuracy results compared to images aligned without GCP. With photogrammetry software, dense point cloud, digital surface model (DSM) and orthophotos can be generated. 3D dense cloud reconstructed in the setting of high accuracy, with millions of points of a rock surface, can be imported into CloudCompare to extract the geological planes using FACET plugin. The major discontinuity sets can be observed and the orientation (dip/dip direction) of the discontinuity sets obtained from the algorithm is accurate and reliable for future geotechnical work such as rock slope stability analysis.

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