- Splinter Historical   (virtual room E)

A simple toolkit for virtual globes

Georg Zotti
Ludwig Boltzmann Institute for Archaeological Prospection and Virtual Archaeology, Vienna, Austria

A classical tool for simulating the orientation of the celestial sphere at a particular time and location was the celestial globe. Nowadays largely replaced by simple stellar planispheres and computer desktop planetarium programs, existing historical globes are mostly kept in museums and are off-limits for regular visitors who are thus limited to seeing just a small part of the whole globe. Globes were often produced by affixing paper gores onto spheres made from wood or plaster. Where copper printing plates or raw prints survived, it is nowadays moderately simple to scan and combine the gores digitally into complete maps of the sky as the creator had intended to show. However, dedicated mapping tools like ArcGIS may not be affordable for most historians. Some years ago I have created a tool set to rapidly create interactively movable digital globes from scanned gores that ideally should show a coordinate grid. Grid point coordinates in a scanned map are just clicked in a web browser window. The resulting text file describes the grid coordinates and associated pixel coordinates (“texture coordinate” in 3D computer graphics terminology). A converter program then generates a virtual globe in the widely used Wavefront OBJ 3D model format. Apart from globe gores, any map that covers a significant part of a globe and that shows a coordinate grid, like Ptolemy’s world maps in medieval manuscripts or various early world maps from the age of discovery offers itself for conversion into at least a partial globe. It is also possible to process good photographs taken from real globes and assemble them into a virtual representation when the grid shown on the globe is reasonably dense. This allows for studying the map image where some globe makers like Vincenzo Coronelli (1650-1718) have added information relevant for their time, like comet paths. The resulting virtual globe can be used in many 3D contexts like Virtual Reality representations of historical buildings with working inventory, demonstrations, or just displayed on a museum’s collection website. I have made a few virtual globes for my private website at https://homepage.univie.ac.at/Georg.Zotti/virtual_globes/index.html