 |
GRASS Help System |
CHARACTERISTICS OF DMA'S DTED-1 ELEVATION DATA
A digital elevation data file consists of a sampled array of elevations
for ground positions that are generally at regularly-spaced intervals.
The Defense Mapping Agency (DMA) produces an elevation product called
Digital Terrain Elevation Data (DTED). DTED is available in two levels,
DTED-1 and DTED-2. The level refers to the resolution of the elevation
data. The resolution is the amount of space between each sample elevation
point in the data file. DTED-1 has a resolution of roughly 100 meters,
while DTED-2 has a resolution of roughly 30 meters.
Although Both the DMA and the USGS distribute DTED data, each distributes
it in a different tape format. The program you use to extract DTED data
from tape will therefore depend upon your source of the data (DMA or USGS).
DTED-1 characteristics are given below:
The unit of coverage is a 1-degreeX 1-degree block. This
corresponds to the east or west half of a 1:250,000 USGS map
sheet. However, these blocks are referenced by their
southwest corner coordinates (Lat., Long.) rather than by
the names of the corresponding USGS map sheets.
* Coverage is available for many regions worldwide, although
predominantly for those within the Northern Hemisphere.
* The data are ordered from south to north in profiles that are
ordered from west to east.
* Elevation points along each profile are spaced at intervals of
3 arc-seconds (roughly 100 meters). This provides for
a 100 meter resolution data file. The information content
is approximately equivalent to the contour information on a
1:250,000 scale map.
* Spacing of the elevation points between each profile varies by
latitude. From 0 degrees N to 50 degrees N, the spacing is
3 arc-seconds. From 50 degrees N to 70 degrees N, the spacing
is 6 arc-seconds. North of 70 degrees N, the spacing is
9 arc-seconds.
* Elevations are stated in meters relative to mean sea level.
GRASS Help
GRASS Documentation
GRASS WWW Home
Please use your browser buttons to navigate this documentation!
Automatically created on: Tue Mar 30 00:23:51 2004