Gerard Tyra - SA Technology (gtyra++at++cts.com)
Tue, 1 Apr 1997 10:20:24 -0800 (PST)
A little background information.
DTED is made up of 1 degree by 1 degree cells, 1 cell per file. The
terrain elevation within the cell is sampled at 3 arc second intervals in
latitude and longitude (at higher latitudes the sampling rate in longitude
drops off) for an effective resolution of approximately 100 meters. The
absolute resolution in position is listed as 30 meters.
This, by the way, is for class 1C data. Higher resolution data exists,
but it is very difficult to get even with an applicable contract with the US
Department of Defense.
DFAD is a vector definition of terrain features, both natural and
cultural. It was originally developed for radar applications. As such,
combining it with DTED can cause some very strange artifacts, like rivers
on the sides of hills. Some of the more interesting features, such as
urban areas, are just listed as an enclosed area, not very useful for a
visualization.
Since both of these formats are based on sampled data, there is a fairly
extensive conversion to viewable data. For most applications, a complete
coversion will generate enough geometry to overload any current
machine. Therefore, a runtime loader is not appropriate. If you want
to use the data, I suggest looking at a modeler such as Multigen or
Designer's Work Bench.
Gerry
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