Common problems encountered in 3D mapping of geological contacts using high-resolution terrain and image data

Abstract

An experiment has been carried out to find a reliable method to map 3D geological contacts using high-resolution Digital Elevation Models (DEMs) and pictures. Various airborne and ground-based photos, and a classical geological map, have been draped by several users on DEMs of the Scex Rouge Mountain (Vaud, Swiss Alps) producing several 3D textured models of the relief. On each of these photorealistic models, geological contacts were then drawn as polylines by hand. The locations of resulting polylines have been then compared. The draping procedure, actually the choice of pairs of control points used for the texturing step, appears to be the main source of discrepancies between the results of the different models. The subjectivity of users in drawing polylines is of lesser importance. We observed also that the widely accepted geological map of the area does not provide an accurate representation of the local geology in steep areas, especially near-vertical rock faces where this effect is marked. Even if high quality and high-resolution data are becoming increasingly more available, a robust way to map geological structures directly in 3D is still lacking. In addition, there is a crucial lack of tools, with editing capabilities able to handle large point cloud datasets and gigapixel images. Finally, the methodology described in this Technical Note is intended to be useful for modelling simple geological structures, such as cylindrical folds, in a complex environment comprising near-vertical rock faces.

Keywords:

• 3D geological mapping
• digital outcrop
• LiDAR
• gigapixel photography