Difference between revisions of "HOWTO import USGS elevation data"

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The US Geological Survey offers a variety of digital elevation models through the [http://seamless.usgs.gov/website/seamless/viewer.php Seamless Distribution System]. Here is an approach to working with them in GRASS.
The US Geological Survey offers a variety of digital elevation models through the [http://seamless.usgs.gov/website/seamless/viewer.php Seamless Distribution System]. The highest resolution offered is 1/9 second (= about 3 meters) with limited coverage of the USA. Most areas not covered by 1/9 arc-second are covered in 1/3 arc-second, with roughly 10-meter resolution. Here is an approach to working with them in GRASS.


== Importing USGS 1/3" NED datasets into GRASS ==
== Importing USGS 1/3 arc second NED datasets into GRASS ==


1. Download the datasets you desire. They will arrive in a zip archive of a directory containing a subdirectory containing a file called w001001.adf, which is the main data file (tip: this is the biggest file).
1. '''Download the datasets you desire''' through the provided web interface. They will arrive in a zip archive of a directory containing a subdirectory containing a file called w001001.adf, which is the main data file (tip: this is the biggest file).


2. '''Create a new GRASS location to work with the DEMs.'''
2. '''Create a new GRASS location to work with the DEMs.'''
<BR>From a GRASS shell:
<BR>Pick one DEM to start with. From a GRASS shell:
: <code>cd 18437824/18437824</code>  ''(example directory names --- replace with your actual names)''
: <code>cd 18437824/18437824</code>  ''(example directory names --- replace with your actual names)''
: <code>r.in.gdal location=''name_of_your_new_location'' in=w001001.adf out=dem</code>
: <code>r.in.gdal location=''name_of_your_new_location'' in=w001001.adf out=dem</code>


3. (re)Start GRASS in the new location.
3. '''Start GRASS''' (or restart) in the new location.
: <code>grass name_of_your_new_location/PERMANENT</code>


4. Import additional files as needed (note the <code>-e</code> flag causing the location's bounds to be extended as needed):
4. If you have more than one DEM archive, import additional files as needed (note the <code>-e</code> flag, which causes the location's bounds to be extended to accomodate the new data):
: <code>r.in.gdal -e in=w001001.adf out=dem2</code>
: <code>r.in.gdal -e in=w001001.adf out=dem2</code>
: ''.. etc.''
: ''.. etc.''


5. Use r.patch to combine the tiles into one continuous map, if desired.
5. Use r.patch to combine the tiles into one continuous map, if desired.
==Alternatives to the USGS DEM data==
Other sources of digital elevation models include:
* SRTM: [[HOWTO import SRTM elevation data]]


[[Category:FAQ]]
[[Category:FAQ]]
[[Category: Import]]
[[Category:HowTo]]

Latest revision as of 14:08, 7 August 2013

The US Geological Survey offers a variety of digital elevation models through the Seamless Distribution System. The highest resolution offered is 1/9 second (= about 3 meters) with limited coverage of the USA. Most areas not covered by 1/9 arc-second are covered in 1/3 arc-second, with roughly 10-meter resolution. Here is an approach to working with them in GRASS.

Importing USGS 1/3 arc second NED datasets into GRASS

1. Download the datasets you desire through the provided web interface. They will arrive in a zip archive of a directory containing a subdirectory containing a file called w001001.adf, which is the main data file (tip: this is the biggest file).

2. Create a new GRASS location to work with the DEMs.
Pick one DEM to start with. From a GRASS shell:

cd 18437824/18437824 (example directory names --- replace with your actual names)
r.in.gdal location=name_of_your_new_location in=w001001.adf out=dem

3. Start GRASS (or restart) in the new location.

grass name_of_your_new_location/PERMANENT

4. If you have more than one DEM archive, import additional files as needed (note the -e flag, which causes the location's bounds to be extended to accomodate the new data):

r.in.gdal -e in=w001001.adf out=dem2
.. etc.

5. Use r.patch to combine the tiles into one continuous map, if desired.

Alternatives to the USGS DEM data

Other sources of digital elevation models include: