Historically, geologists used stereoscopes to study large-scale aerial photographs, as an aid to field reconnaissance (Pillmore 1989) and to map regional stratigraphic frameworks on well exposed geological outcrops (e.g. Sgavetti 1992; Lebel and de Roza 1999). Technological advances using analytical plotters interfaced with computers, could only generate Digital Elevation Models (DEMs) as the final product (Pringle et al. in review).
Digital photogrammetry, using VirtuoZo software supplied by Supresoft Inc., converts scanned aerial photographic images into 3D digital models. Digital Terrain Models (DTMs) are produced, which give more accurate representation of the topographic surface, with the image pixel positions re-projected to form a geographically referenced Ortho-Rectified Image (ORI) in 2D. The generation of ORIs from stereo photographs removes inaccuracies associated with lens distortion and other photographic effects, which is vital for accurate measurements. The ORIs are then draped over the interpolated DEMs to produce a three dimensional, high resolution, dynamic stereo-model (Figure 2). Multiple users can view the same image for example, by wearing polarised viewing glasses combined with a stereoscopic screen filter which covers the workstation screen (Figure 3). The 3-D model and rectified photographic imagery can then be shared with a wider, non-specialised peer group, none of whom need photogrammetric skills.