Abstract: Georgia Tech has developed the Virtual GIS (VGIS) system, a real time visualization system for terrain, image, and geographic information systems (GIS) data sets. The initial systems developed at Georgia Tech were non- realtime, but had fast generation of perspective scenes from multisources data sets and the ability to query for GIS attributes associated with terrain of 3D structures inserted within the terrain. The basic concept of a virtual GIS was implemented in realtime using the Silicon Graphics International graphics language. This system has been extended in capability to allow realtime traversal within a very large geographic database and to show the finest detail information available when it is near to the view point. Extensive work has been done in the management of large arrays of information and the efficient paging of that information into the rendering system. An effective level of detail management system is implemented to dynamically allocate the appropriate amount of detail relative to the viewer location. A major use of this system has been in the area of battlefield visualization. The advent of OpenGL as a defacto standard has now made it possible to provide the VGIS capacity on a number of other platforms, thereby extending its usefulness to other applications and users. OpenGL has been developed as a general purpose Graphics rendering toolkit that will be supported on various computers and special purpose rendering systems. There are hardware and software implementations of OpenGL. This should allow VGIS to operate on many systems, taking advantage of specialized graphics hardware when it is present. This paper addresses the implementation of the VGIS system in OpenGL and the use of the system in driving the Evans and Sutherland Freedom series graphics rendering hardware. !25
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