3D model generated from UAV photogrammetry and semi-automated rock mass characterization

This work develops a rock mass characterization of a limestone quarry in northern Spain based on a 3D model obtained by using photographs taken from an unmanned aerial vehicle (UAV) flight and structure-from-motion algorithms. This methodology permits to obtain photogrammetric information in a rapid and low-cost way. Geological planar facets (stratification, faults) are related to the tectonic history of a geological formation and permit assessing slope stability. The spatial orientation of planar features is usually measured with a compass and clinometer, which requires experience and knowledge, it is space limited, and sometimes hazardous. Geological 3D models can mitigate these limitations. A 3D point cloud generated from a series of images obtained using an UAV is included in the open-access applications DSE and FACET, which serve to determine the main discontinuity planes within a limestone quarry. Comparison of the results from software analyses with data handmeasured directly in the field reveals the effectiveness of the use of UAV to develop a virtual outcrop model that permits to obtain accurate measurements. The resultant quarry 3D model has been included in Sketchfab, an open access platform that permits easy and quick access and availability for a wide audience. This study shows that the use of UAV combined with structure-from-motion algorithms is of great interest for geosciences as well as other related disciplines such as mining or civil engineering, and can facilitate decisionmaking for policy makers and authorities. In addition, it is a technique of great use to develop rock mass characterization in a low-cost, rapid, and easy way, and permits to reach areas with difficult accessibility. This way, this methodology can also be very useful for geosciences teaching purposes, as a complement to traditional field lectures, or to develop virtual field trips and laboratories.