# GRASS Help System

## EXTRACTING DIGITAL ELEVATION DATA

Elevation data are used in a variety of GRASS applications. Alone, they can be used to generate maps of slope, aspect, and 3-D graphics. They can also be used in combination with other data types as, for example, with vegetation or soils to delineate species' habitats or correlate changes in vegetation or soil types with elevation. Other applications include hydrologic modeling, soil erosion evaluation and prediction, and line of sight analyses. Before such data can be used, however, they must be converted to a raster format usable within GRASS. "DTED and DEM Elevation Data Extraction" describes specific procedures by which users can convert digital elevation data produced by the Defense Mapping Agency (DMA) and the U.S. Geological Survey (USGS) into GRASS raster format. It also details processes for generating slope and aspect raster map layers from the imported elevation data, and for rescaling these elevation data.

See also "Options for Acquiring Elevation Data" for a more detailed look at how elevation data are produced and the forms in which they are available.

The U.S. Geological Survey (USGS) and the Defense Mapping Agency (DMA) distribute digital elevation data at several resolutions and in different tape formats. These data are referred to as digital elevation models (DEMs) and digital terrain elevation data (DTED). The GRASS programs listed below extract this data from 1/2" magnetic tape, list tape contents and rotate the data.

- m.examine.tape - m.dted.examine
- m.dem.examine - m.dted.extract
- m.dem.extract - m.rot90
- m.dmaUSGSread

For more information on a specific command, select a command and press ESC.

For more information on the different digital elevation data products, production methods, and distribution information available from the USGS, DMA or private comapanies, select an area from the list below.

1) Elevation Data Distributed by the USGS
2) Elevation Data Distributed by the DMA
3) Elevation Data Distributed by Private Companies

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