Changes between Version 5 and Version 6 of Processing/SRTMDEMs

Timestamp:

Sep 9, 2010, 3:26:57 PM (14 years ago)

Author:

benj

Comment:

--

Processing/SRTMDEMs

@@ -1 @@
-== Creating DEMs from SRTM data ==
+== Creating DEMs from ASTER or SRTM data ==
 
-The Shuttle Radar Topography Mission mapped global elevations at a 3 arc second (90m posting) resolution between 60N and 56S. This is relatively coarse for DEM usage but is sufficient in some cases. To create a DEM from this data:
+The ASTER GDEM is a global elevation dataset at 1-arc-second (30m) horizontal resolution, covering the earth from 83S-83N. More data about the dataset is available at http://www.ersdac.or.jp/GDEM/E/2.html, the dataset itself can be downloaded from http://asterweb.jpl.nasa.gov/gdem-wist.asp.
 
-1. Obtain data from SRTM ([http://srtm.usgs.gov/ http://srtm.usgs.gov/]). This is most easily done via their [http://earthexplorer.usgs.gov Earth Explorer] - expand the "Digital Elevation" link on the left and tick the box labelled "SRTM". Enter bounding co-ordinates for the area you want data for, clicking the green "+" icon after each one. Note that this currently seems not to always work correctly for locations in DMS format (at least in Firefox), you may need to switch to decimal degrees (which work fine). Click on the "Search" button in the bottom-right, and you should be presented with a list of items matching your search (there should be only one thing in it). Click on the "SRTM" link (you may need to enable pop-ups if you've got them blocked), and you will be presented with a list of matching SRTM tiles and download links - download the data you want to use. Note that only SRTM 3-arc-second resolution data is available for sites outside North America. For sites in North America higher resolution data can be obtained via the USGS [http://seamless.usgs.gov/ Seamless Server]
+The Shuttle Radar Topography Mission mapped global elevations at a 3 arc second (90m posting) resolution between 60N and 56S. More information is available from http://srtm.usgs.gov/, and the data are available via the [http://earthexplorer.usgs.gov USGS Earth Explorer]
 
-2. Unzip the downloaded zip file and descend into the directory structure to find the file w001001.adf - this holds the actual data, though you can't move it without the rest of the directory structure.
+Both of these are relatively coarse for ARSF DEM usage but are sufficient in some cases. To create a DEM from these data:
+
+1. Obtain DEM data. ASTER should be used in preference to SRTM unless there is a good reason not to.
+ * ASTER from http://asterweb.jpl.nasa.gov/gdem-wist.asp. You will need to register, define the search area you're interested in and create an appropriate data order.
+ * SRTM from http://earthexplorer.usgs.gov. Expand the "Digital Elevation" link on the left and tick the box labelled "SRTM". Enter bounding co-ordinates for the area you want data for, clicking the green "+" icon after each one. Note that this currently seems not to always work correctly for locations in DMS format (at least in Firefox), you may need to switch to decimal degrees (which work fine). Click on the "Search" button in the bottom-right, and you should be presented with a list of items matching your search (there should be only one thing in it). Click on the "SRTM" link (you may need to enable pop-ups if you've got them blocked), and you will be presented with a list of matching SRTM tiles and download links - download the data you want to use. Note that only SRTM 3-arc-second resolution data is available for sites outside North America. For sites in North America higher resolution data can be obtained via the USGS [http://seamless.usgs.gov/ Seamless Server]
+
+2. Unzip the downloaded zip file. ASTER data will contain two GeoTIFFs (you want the "_dem" one). For SRTM data, descend into the directory structure to find the file w001001.adf - this holds the actual data, though you can't move it without the rest of the directory structure.
 
 3. Fire up Grass. Select a location in lat/long projection using WGS84 datum (create one if none avaialble), make a note of the selected location and mapset names.
 
-4. Import the SRTM data file:
+4. Import the data file:
+For ASTER data:
+{{{
+r.in.gdal input=<aster_tile>_dem.tif output=aster_data
+}}}
+For SRTM data:
 {{{
 r.in.gdal input=w001001.adf output=srtm_data