A Method for Acquiring and Processing Ground-Based LiDAR Data in Difficult to Access Outcrops for use in 3-D Virtual-Reality Models

Florence L. Bonnaffé, David C. Jennette, John R. Andrews, David R. Pyles, Renaud Bouroullec, and Mark Tomasso
Bureau of Economic Geology, John A. & Katherine G. Jackson School of Geosciences, Austin, TX

LiDAR (light detection and ranging) data provide a cm-scale resolution digital outcrop model. This technology supplements and improves conventional outcrop investigations by providing geoscientists ways to digitally visit and analyze outcrops on their computer or workstation.

Our current processing workflow includes the creation of an optimized triangulated surface onto which high resolution photographs are rectified and draped. To obtain optimum resolution, LiDAR data should be acquired along a direction perpendicular to the outcrop face. Field constraints, such as sea cliffs or exposures without good vantage point, sometimes dictate to scan the outcrop with an oblique direction. Acquiring LiDAR data from an oblique direction creates large shadows (zones of no data) and anomalously elongated triangulated areas. Using a three-dimensional transformation matrix that modifies the direction of triangulation, we can correct for these effects. This procedure allows to obtain an optimized triangulated surface as if it were shot from an inaccessible angle, without altering the position or density of the original digital data. This angle correction method is essential for accurate photo draping and virtual reality model creation.

This methodology can be especially beneficial for cases where the stratigraphic interpretation is carried out directly on photodraped 3-D models. In addition, vegetation and other obstacles altering the view of the exposures can be digitally removed to create a perfectly continuous outcrop rendering that greatly help stratigraphic analysis and mapping of sedimentary bodies.