Structural and Orientation Analysis of 3D Virtual Outcrop Models

Two methods are currently used to create photorealistic 3D virtual models of geological outcrops. One method creates a triangulated irregular network (TIN) model from LIDAR point clocud scans of the outcrop and then drapes photographs of the outcrop onto the TIN model. The other method uses stereo-pair photographs of the outcrop and creates the model using methods derived from aerial photogrammetry techniques. Both approaches result in a TIN model with a photographic image of the outcrop draped on the TIN model. Software modules have been created which enable the analysis of the orientation and structural characteristics of such 3D outcrop models. The models are first georeferenced in world coordinates. Then, strike-dip values are computed from the orientation of selected triangles or points on a planar surface or by picking points along the contact edge of two bedding layers which have dimensional relief from erosion. Trend-plunge values are computed from the intersection of two strike-dip planes or from the selection of two points along a linear feature. Fold cross-sectional profiles are created by projecting points selected along the edge of the fold onto a plane perpendicular to the fold trend-plunge direction. Bedding thickness is measured by selecting a point on one edge of a bed and projecting it to the strike-dip plane of the other edge of the bed. Orientation of all of the surfaces of the model can be automatically classified and color coded based upon specified orientation values. These algorithms have been implemented in ArcGIS software platform using the ArcScene interface. The TIN models are first converted into an ESRI multipatch format. The model is then accessible for viewing and analysis using the GeoDimensional extension to the ArcGIS software that we have developed. The tool set will be ported to an open source software platform over the coming year.