Development and assessment of a photogrammetry system for rock specimen surface characterization

The use of field and laboratory three-dimensional imaging techniques are commonly used to assess the roughness of planar rock joint surfaces for shear strength estimations. A photogrammetry system for capturing the surface features of cylindrical rock specimens is presented. They system consists of a DSLR camera, photo-turntable, scale block, photogrammetry software and point cloud processing software. The process to develop a cylinder shaped point cloud, unwrap the point cloud, and triangulate the unwrapped point cloud is presented. The photogrammetry system was assessed using a smooth limestone specimen as a benchmark. Increasing the number of digital images used to generate the point cloud increased the number of points in the point cloud. However the increase in the number of point significantly decreased when using more than eight digital images. A minimum of six digital images are required to fully capture the surface of the specimen. The computing time ranged between ten and twenty-four minutes to generate a point cloud consisting of approximately twenty million data points using twenty-four digital images.