A method for acquiring and processing ground-based lidar data in difficult-to-access outcrops for use in three-dimensional, virtual-reality models

Abstract

Lidar (light detection and ranging) data provide a centimeter-scale-resolution digital outcrop model. This technology supplements and improves conventional outcrop investigations by providing ways for geoscientists to digitally visit and analyze outcrops on their computers or workstations. Our current processing workflow includes creation of an optimized, triangulated surface, onto which high-resolution photographs are rectified and draped. For optimal resolution, lidar data should be acquired along a direction perpendicular to the outcrop face. Field constraints, such as sea cliffs or exposures without a good vantage point, sometimes necessitate scanning the outcrop in an oblique direction. And yet 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 elongated triangles. In addition, combining multiple scans shot from different angles minimizes data shadow. This procedure lets us 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 to accurate photo draping and virtual-reality model creation. © 2007 Geological Society of America.