Reconnaissance Documentation of Geologic Structure Using Close-Range Terrestrial Photogrammetry: Fid-Bau Portal

Reconnaissance Documentation of Geologic Structure Using Close-Range Terrestrial Photogrammetry

Romo, Pierre E. / Keaton, Jeffrey R.

Terrestrial photogrammetry is a useful tool for reconnaissance-level documentation of slopes in general and of slopes with exposed rock formations in particular. There are several manufacturers of terrestrial photogrammetry systems currently on the market, i.e. Sirovision, Adam Technology, and 3GSM ShapeMetrix3D. Ultimately, they all deliver a similar product to the end user, albeit different field procedures, resolution, and cost. The system by 3GSM (Graz, Austria) used for examples in this paper consists of an optically stable, calibrated digital camera and zoom lens, a range pole, a ground target, and ShapeMetriX3D software. Pairs of photographs taken from two arbitrary camera positions spaced at approximately 20 percent of the distance from the camera baseline to the slope being documented can be used to produce three-dimensional (3D) models suitable for measuring orientations of exposed geologic structures, positions of points, distances between points, and profiles of the model surface on planes of any orientation. The system produces the best results with steep quarries, cliffs, and road cuts that are no more than about 50 m from the camera and is unsuitable for modeling slopes that are distant or obscured by vegetation or dust. Measurements extracted from models of adjacent or nearby slopes can be combined for engineering geologic analyses provided that the models are normalized, rotated to a common north orientation, and translated to a common coordinate system (e.g., UTM or arbitrary). Lower-hemisphere projections of orientation data can be plotted and analyzed with a module in ShapeMetriX3D and exported for manipulation in other software. Measurements of dimensions can be used for characterizing joint spacing and block size. Extracted model-surface profiles can be imported into spreadsheet and GIS software to characterize joint roughness. Rock slope engineering analyses of a highway cut slope and engineering geologic analysis of a sea cliff are used as examples of the technology. This paper will follow the basic procedures for making 3D models and case studies using the 3GSM system.