Laboratory 3D rock joint roughness evaluation with basic, uncomplicated close-range photogrammetry

Abstract

Photogrammetry-based methods using everyday, easily available photographic equipment and free software have gained relevance for roughness measurement of rock joints. However, the influence of some aspects, such as the number and orientation of camera poses, the parameters of the Structure-from-Motion (SfM), Multi-View Stereo (MVS) and meshing algorithms, which influence the resolution and accuracy of the reconstructed models, require proper appraisal. To assess the surface roughness of a granite rock joint specimen using such photogrammetry methods, 3D models generated using different settings (i.e., camera sensors, camera poses, open/free software and workflows), were compared with a reference model obtained by contact digitization. The results suggest that comparable results can be achieved if the photos adequately cover the specimen and, at least, equivalent vertex densities are attained. Percentiles p5 and p95 of surface deviations of the tested models to the reference mesh were, in general, lower than ±0.1 mm. Results also showed that this methodology is far more accessible, easier to use, faster to implement, and less expensive than most currently available equipment and approaches.