A SELF-DRIVE VIRTUAL FIELD TRIP TO THE VREDEFORT IMPACT STRUCTURE, S.A., INCORPORATING VIRTUAL SPECIMENS AND DIGITIZED LEGACY MAPPING DATA

For her master’s thesis, Simpson (1977) studied the structure of the Vredefort Rim Synclinorium, part of the world’s oldest preserved impact structure located southwest of Johannesburg, S.A. Her maps, photographs, and field notes have been stored in laboratory drawers ever since then. Using “map inversion” concepts from De Paor and Sharma (2007) – see also Simpson and De Paor (2010) – we created a Google Earth virtual field trip featuring: (i) scanned maps draped over the Google Earth digital terrain model using the "Add...image overlay" menu item; (ii) georeferenced field notes and scanned field photographs imported via the “add...photo” menu item; (iii) emergent cross sections created in Google SketchUp and imported as COLLADA models; and (iv) virtual specimens scanned from thesis rock samples. The latter were made with a NextEngine 3-D laser scanner that uses laser triangulation and two cameras to drape high-resolution images over a wire mesh model. 3-D object files are exported to MeshLab software, and then imported into the Google Earth API as COLLADA models. KML commands control the position, size, and orientation of each specimen. Models can be manipulated using Javascript slider controls on associated HTML5 web pages. An innovative aspect of this virtual field trip is the use of a COLLADA model of a “self-drive” field vehicle that students control, thus emulating real field experience more closely than traditional virtual field trips. On the self-drive virtual field trip, students steer a virtual Jeep to a field location where they can view the above virtual specimens, map overlays, and original images of the site. Virtual specimens become visible when the virtual field vehicle is in close proximity of source outcrops. Very few students or even professionals get to visit Vredefort in person and given that it is now a UNESCO World Heritage Site, those who do visit are discouraged from casual specimen collection. By making scanned virtual specimens available over the Internet, students from every corner of the Earth can see close-up views of pseudotachylite and shatter cone structures associated with the impact.

References:

Simpson, C. 1977. M.Sc. Thesis, Univ of Witwatersrand, 257p

De Paor D. G. and Sharma, A. 2007. G.S.A. Abstr. with Progs, 39 - 41.

Simpson C. and De Paor, D.G. 2010. Geol. Soc. Lond. Spec. Pub. 335, 429–441.