Abstract
This work presents the development of a three-dimensional (3D) model of an outcrop of the Corumbataí Formation (Permian, Paraná Basin, Brazil) using Structure from Motion - Multi-View Stereo (SfM-MVS) technique in order to provide a structural analysis of clastic dikes cutting through siltstone layers. While traditional photogrammetry requires the user to input a series of parameters related to the camera orientation and its characteristics (such as focal distance), in SfM-MVS the scene geometry, camera position and orientations are automatically determined by a bundle adjustment, an iterative procedure based on a set of overlapping images. It is considered a low-cost technique in terms of hardware and software, also being able to provide point density and accuracy on par to the ones obtained withTerrestrial Laser Scanning. The results acquired on this research have good agreement with previous works, yielding a NNW main orientation for the dikes measured in the field and on the 3D model. The development of this work showed that SfM-MVS use and practice on geosciences still needs more studies on the optimization of the involved parameters (such as camera orientation, image overlap and angle of illumination), which, when accomplished, will result in less processing time and more accurate models.
Highlights
In geology, the understanding of structures can be too complex to be reached using only field methods
Considering that the use of Structure from Motion - Multi-View Stereo (SfM-MultiView Stereo (MVS)) in the geosciences is expanding rapidly, and that a successful Digital Outcrop Model (DOM) generation might involve more factors than initially considered by the non-experienced user, we present a brief summary of the processes and algorithms involved in the SfMMVS workflow, as well a list of best practices for fieldwork, derived from the experience gained by the authors in the development of this project
The mesh — usually a Triangulated Irregular Network (TIN) — can receive a texture provided by the photographs (Hanusch 2008), that assigns real-world color to the digital surface
Summary
The understanding of structures can be too complex to be reached using only field methods. ■■ Three-dimensional (3D) outcrop navigation/exploration, providing “access”to out-of-reach or hazardous areas. Among such techniques, SfM-MVS (Structure from Motion - Multi-View Stereo) workflow has gained strength in the geosciences over the past years (Tab. 1), mostly because when compared to other digital surveying it is capable of producing high-resolution data at low cost, fast and virtually independent of spatial scale. An example of a complex structure that can take advantage of the use of SfM-MVS are clastic dikes, which are discordant subvertical sheets, tabular bodies of clastic sediments that can form by hydraulic fracturing and infilling (Hargitai & Levi 2014). Even for traditional field survey, the analysis of such structures can be challenging and, to date, no work has presented it through the use of 3D models
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