Digital Earth Workbench is a computer program that facilitates retrieval of Earth-related imagery and viewing of the imagery on either an ordinary computer video screen or a virtual-reality (head-tracked stereoscopic) display system. Examples of imagery that can be processed by
this software include (but are not limited to) high-resolution topography, photographic images, maps, and images synthesized from geophysical data. Image data can be retrieved from storage at remote sites. The user can easily navigate to the data pertinent to any location on Earth and browse through imagery for that location. For images that are not topographical, the user can view the images overlaid on high-resolution Earth topography.
The development of Digital Earth Workbench was prompted by a desire for a system that is simple enough for use by a child and powerful enough to be useful to a scientist and that, in comparison with similar prior software, offers faster processing of image data and better performance as a virtual-reality interface. Digital Earth Workbench incorporates software components that exploit the capabilities of advanced computer hardware, mediate the exchange of data with virtual-reality display systems, implement advanced rendering concepts, and generate real-time graphical displays. These components are integrated in such a way as to focus them on displaying Earth-science data. The virtual-reality components of this software are particularly valuable because they provide an easy-to-use interface for obtaining three-dimensional-appearing views of data in relation to the Earth.
In this software, the topography of the entire surface of the Earth is divided into tiles. Each tile is further divided into subtiles. Each tile and subtile provide representations of the topography at several different levels of detail. As the user roams through geographically indexed data, the appropriate tiles, subtiles, and level of detail of each are selected on the basis of their proximity to the location selected by the user: this selection scheme limits the amount of graphical information that must be processed, so that the frame rate can remain high.
For overlaying images on Earth topography (and/or on a corresponding base Earth image), the software utilizes a multipass rendering mechanism. After the components of an overlay have been set up, the topography is redrawn, using the overlay information as texture superimposed on the topography. The redrawing process is limited to the largest topographical tile or subtile needed to encompass the overlay, in order to minimize the amount of geometrical information that must be processed. Multiple overlays are blended by use of common translucency techniques.
This work was done by Stephen Maher of Goddard Space Flight Center. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Software category.
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