DIGITAL CLOSE RANGE PHOTOGRAMMETRY AS PART OF A TERRESTRIAL BASED DIGITAL GEOLOGIC MAPPING PROGRAM

The 3D modeling program at the University of Texas at Dallas, is exploring the application of 3D virtual models derived from both laser scanning and photogrammetric techniques. Photogrammetry compliments the development work based upon the creation and analysis of 3D virtual models of geological outcrops which are derived from the overlaying (draping) of photographs onto Triangulated Irregular Networks (TIN) from laser scans. The photogrammetric method has the capability of providing very high resolution models. With proper controls the models can be used for spatial measurements. Both Sirovision® and Photomodeler® are being evaluated for this purpose. Initially, models were built using a single camera method using tape measures and low resolution laser range finders for survey control. This effort is being extended to explore the use of a two camera system with high resolution survey measurements using a total station and RTK GPS. The two camera system is essential to long range photogrammetry because the lighting environment, which strongly affects the model building, often changes as a single camera is moved over distances of 10's to 100's of meters (the distance between camera setups must be approximately 1/7 of the distance to the target). In addition, the benefits of using a custom made stable camera platform mounted on survey tripods and incorporating reflector prisms for maximum accuracy in surveying the camera locations are being explored. The intent of the program is to merge small area high resolution photogrammetric models with lower resolution large area models to provide a hybrid model which conveys both the large scale attributes of the site with the high resolution attributes needed for detailed structural analysis of the site. This method is being tested at several sites in the Texas-Oklahoma area.