Workflow: From photo-based 3-D reconstruction of remotely piloted aircraft images to a 3-D geological model

Abstract

Geological field mapping is a vital first step in understanding geological processes. During the 20th century, mapping was revolutionized through advances in remote sensing technology. With the recent availability of low-cost remotely piloted aircraft (RPA), field geologists now routinely carry out aerial imaging without the need to use satellite, helicopter, or airplane systems. RPA photographs are processed by photo-based three-dimensional (3-D) reconstruction software, which uses structure-from-motion and multi-view stereo algorithms to create an ultra-high-resolution, 3-D point cloud of a region or target outcrop. These point clouds are analyzed to extract the orientation of geological structures and strata, and are also used to create digital elevation models and photorealistic 3-D models. However, this technique has only recently been used for structural mapping. Here, we outline a workflow starting with RPA data acquisition, followed by photo-based 3-D reconstruction, and ending with a 3-D geological model. The Jabal Hafit anticline in the United Arab Emirates was selected to demonstrate this workflow. At this anticline, outcrop exposure is excellent and the terrain is challenging to navigate due to areas of high relief. This makes for an ideal RPA mapping site and provides a good indication of how practical this method may be for the field geologist. Results confirm that RPA photo-based 3-D reconstruction mapping is an accurate and cost-efficient remote sensing method for geological mapping.

Mapping the fracture network in the Lilstock pavement, Bristol Channel, UK: manual versus automatic

“…Several tectonic phases are inferred from the structures found in the Bristol Channel basin, starting with two events of N-S extension, in the Jurassic to Early Cretaceous and Late Cretaceous to Oligocene, followed by Alpine N-S contraction from the late Oligocene to Miocene and the progressive relaxation during the Late Miocene or post-Miocene (Rawnsley et al, 1998). These events are recorded as conjugate E-W-striking normal faults (Brooks et al, 1988) caused by the extension and conjugate strike-slip faults along with inverted normal faults, which resulted from the subsequent compression (Dart et al, 1995;Glen et al, 2005;Kelly et al, 1999;Nemčok et al, 1995). This study focuses on mode I joints in the limestone layers, which have been studied by Agheshlui et al (2018), Azizmohammadi and Matthäi (2017), Belayneh et al (2006a, b), Belayneh and Cosgrove (2004), Engelder and Peacock (2001), Gillespie et al (2011), Loosveld and Franssen (1992), Matthäi et al (2007), Matthäi and Belayneh (2004), and Peacock and Sanderson (1991, 1994.…”

Automatic and Manual Fracture-Lineament Identification on Digital Surface Models as Methods for Collecting Fracture Data on Outcrops: Case Study on Fractured Granite Outcrops, Bangka

“…In this study, a DJI Mavic Pro drone with a 12-megapixel mounted camera is used to capture sets of images of the outcrops during fieldwork. The images are later processed using Structure-from-Motion (SfM) photogrammetry (Westoby et al, 2015;Madjid et al, 2018;Hansman and Ring, 2019) to construct a three-dimensional model. Fracture data of the outcrops have also been collected with the linear scanline method by using a measuring tape and geological compass to later ground truth and validate the results of DSM methods.…”

SfM-MVS Photogrammetry for Rockfall Analysis and Hazard Assessment Along the Ancient Roman Via Flaminia Road at the Furlo Gorge (Italy)

“…This software can solve the camera interior and exterior orientation parameters and generate georeferenced spatial data such as 3D point clouds, DEMs, DTMs and orthophotos. Agisoft™ MetaShape based on (i) SfM technology for the exterior orientation of images and the creation of the sparse 3D point cloud and (ii) MVS photogrammetry for the dense cloud reconstruction [67,68].…”