# GRASS Help System

## CHARACTERISTICS OF DMA'S DTED-2 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-2 Data Characteristics:

* Coverage is limited. Production has only been done for special
projects. Inquire at the DMA about coverage for your
area of interest.
* 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
1 arc-second (roughly 30 meters). This provides for a
30 meter resolution data file. The information content
is approximately equivalent to the contour information on a
1:50,000 scale map.
* Elevations are in meters relative to mean sea level.

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Automatically created on: Thu Oct 14 02:12:26 2004