AN EFFICIENT INTERACTIVE METHOD FOR AUTOMATIC DIGITAL ANALYSIS OF THE ORIENTATIONS OF FAULT AND JOINT STRUCTURES USING 3D VIRTUAL MODELS OF OUTCROPS

The orientations, such as strike-dip, of the structures of a geological outcrop are mapped to stereonets by computing the surface normals to the triangles of the Triangulated Irregular Network (TIN) which models the outcrop morphology. Methods have been developed to create photorealistic 3D virtual models by accurately mapping (draping) photographs onto TIN models derived from point clouds captured by fast terrestrial laser scanners. During this processing, the quality of the resultant photorealistic model is improved by selecting for each TIN triangle the single photograph, among several, which has the smallest angle between the surface normal to the triangle and the camera lens axis. The extraction of these surface normals can also be used to determine the orientation of the surfaces which comprise the TIN model. A more user friendly, interactive method is being developed to perform analysis of faults, joints, and bedding planes, which will allow for the analysis of deformation in the 3D virtual model of the outcrop for research and for in-classroom instruction. The development of this capability will allow an interactive determination of the orientation of selected surfaces, the display of various hinge axes and axial surfaces as well as fault and joint surfaces using planes which cut the model, and the color coding of surfaces with common orientations. When applying this to 3D photorealistic models of outcrops it is possible to select regions of outcrops by their structural domains or lithology for more detailed analyses. The 3D models are displayed in the open-source OpenSceneGraph viewer. Results from analyzing data from Texas, Oklahoma, Arkansas and other locations will be shown.