Virtual outcrop geology comes of age: The application of consumer-grade virtual reality hardware and software to digital outcrop data analysis

In this work, the application of consumer-grade virtual reality (VR) hardware and software to the analysis of digital outcrop data is explored. Here, we utilize a widely available VR hardware platform (HTC Vive) and VR based freeform 3D visual arts software package (Google Tilt Brush), to digitize fault traces from photo-textured digital outcrop models of exposures of the Penrith Sandstone Formation (Lacy's Caves), in northwest England. Using MATLAB routines provided herein, triangular meshes output from Tilt Brush are used as the basis for 3D fracture trace map extraction, which in turn, are used to generate fracture properties (trace length, orientation, areal fracture intensity). We compare the results of this analysis to two equivalent datasets obtained from the Lacy's Caves model using digital outcrop analysis deployed via a conventional flat panel display: namely (1) a 3D trace map extracted using optical ray tracing from manually interpreted calibrated images and (2) 3D traces fitted directly the Lacy's Caves textured mesh using manual polyline interpretation within an established digital outcrop analysis software platform (OpenPlot). Fault statistics obtained using VR based analysis are broadly equivalent to those acquired from 3D trace maps extracted using the flat panel display deployed analyses presented herein. In this case study, it was found that VR based digital outcrop analysis provided faster data acquisition than the comparative pixel-based approach, which requires linkage and merging of traces mapped from multiple contiguous images. Manual raster analysis and optical ray tracing did however provide 3D trace maps with significantly higher areal fault intensity, with VR analysis incurring censoring of finer fault traces, due to the limited resolution of the outcrop model textured mesh. Whilst data acquisition times and resultant fault intensities proved similar between the VR and OpenPlot workflows, it was noted anecdotally, that the VR analysis holds some advantages for the operator when interpreting models exhibiting complex geometries, such as mine workings and caves systems, with the clip point implemented within the viewport of conventional digital outcrop analysis software tools obstructing the user from obtaining an optimum view of the outcrop surface. VR based digital outcrop analysis techniques, such as those presented here, provide an immersive analytical environment to the operator. This allows users to fuse powerful 3D visualizations of photo-realistic outcrop models with geological interpretation and data collection, fulfilling the early promise of ‘virtual outcrops’ as an analytical medium that can emulate traditional fieldwork. It is hoped that this study and its associated code library will facilitate the evaluation of emerging VR technologies for digital outcrop applications, by provided access to VR analytical tools for non-specialists in virtual reality systems. Finally, prospects for the use of VR technology within the field of digital outcrop geology, as well as within the wider geosciences, are also discussed.