Evaluating methods of field-based 3D visualization and their application to mapping metamorphic terranes: An example from the Panamint Mountains, California

Field geology has traditionally relied on 2D, paper-based workflows, but digital mapping techniques are rapidly replacing these outdated methods because they allow for more efficient and accurate mapping. This research applies digital mapping techniques and two terrestrially-based 3D visualization technologies, photogrammetry and Light Detection and Ranging (LiDAR), to the study of metamorphic terranes in the Panamint Mountains, California. This study reports on the spatial accuracy of TINs (triangulated irregular networks) generated from both photogrammetry and ground-based LiDAR using a terrestrial laser scanner (TLS) and discusses how spatial accuracy can be increased. Two levels of comparison were used to test spatial accuracy. First, the TINs generated from photogrammetry were directly compared to those generated from the TLS in 3D space. The second level of comparison involved making geologic interpretations on both the photogrammetrically- and TLS-derived terrain models and qualitatively comparing them in 2D space to interpretations made in the field. In both levels of comparison, spatial accuracy of the photogrammetrically-derived TINs depends primarily on the ratio between the length of the baseline (line that connects the camera positions) and the distance to the farthest feature in the scene, the number and distribution of ground control points, the number of photographs taken, model error, and GPS precision. The final analysis compared orientation measurements taken from LiDAR-derived TINs to orientations taken from the field. Orientations obtained from LiDAR-derived TINs in areas that could not be reached in the field can supplement field orientation, thus filling in data gaps to yield a more complete understanding of the structure. The workflows developed in this research represent a step toward implementing 3D visualizations into field studies, particularly studies of metamorphic terranes. These workflows may change the way geologists approach field work