Photogrammetric Reconstruction of Rock Outcrops using Open Source Software

The purpose of this research is to examine the suitability of digital photogrammetry for mapping and processing the 3D rock structure of hard rock outcrops using consumer-grade digital cameras and open source software.
For this purpose, the camera settings for photogrammetric image acquisition were first optimized, including camera positions and light paths to achieve sufficient overlapping and to minimize shadowing. The open source software VisualSFM was then used to conduct feature detection, match images, and determine the camera positions. The dense point cloud was constructed using open source algorithms based on the approaches of Patch-based Multi-View Stereo (PMVS) and Clustering Views for Multi-View Stereo (CMVS). The open source software SfM_georef was then used to merge point clouds of different outcrops into a common coordinate system. The accuracy of different smartphone apps for determining the coordinates of Ground Control Points (GCP) using Global Position System (GPS) was tested as an alternative to high accuracy Real Time Kinematic (RTK) GPS.
Rock structures were extracted from the point clouds using the open source software CloudCompare. The statistical computing of the set-based geometrical parameters of discontinuities was conducted in open source software environment R. The elaborated processing methods were tested for five outcrops having different rock types and structural fabrics. Discontinuity parameters estimated using the digital models are compared with traditional contact-based measurements. The results show that photogrammetric modelling and open source computing provides enormous cost, time and safety incentives in standard engineering practice.