Difference between revisions of "USGS SDDS"
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Revision as of 11:33, 12 May 2009
The National Elevation Dataset (NED) is a new raster product assembled by the U.S. Geological Survey. NED is designed to provide National elevation data in a seamless form with a consistent datum, elevation unit, and projection. Data corrections were made in the NED assembly process to minimize artifacts, perform edge matching, and fill sliver areas of missing data. NED has a resolution of one arc-second (approximately 30 meters) for the conterminous United States, Hawaii, and Puerto Rico and a resolution of two arc-seconds for Alaska. More info can be found at http://gisdata.usgs.net/NED/.
SRTM 30m and SRTM 90m data is also available from the the USGS Seamless Distribution site. Information on the SRTM data can be found at http://srtm.usgs.gov/ .
How to download
The data can be downloaded at http://seamless.usgs.gov/. There is online help available by clicking help in the upper right corner.
- First click either NED, 1/3 NED, 1/9 NED, SRTM 30m or SRTM 90m under "Download Layers" Uncheck all others.
- Define the area by either clicking the "Select by Rectangle" tool under "Download" or by clicking "Define Area By Coordinates".
- Once the area is defined you will be taken to the download page. You will need to click "Modify Data Request" and change the format to the BIL format. Click "Save Changes & Return to Summary".
- Click "Download". You will be prompted to save the file once it is ready for download
How to use the seamless NED and SRTM data with the Pathloss program.
Decompress the dataset to its own directory. The dataset is comprised of 10 files…
| *.BIL | METADATA.DBF |
| *.BLW | METADATA.PRJ |
| *.HDR | METADATA.SHP |
| *.PRJ | METADATA.SHX |
| *.STX | METADATA.TEX |
The NED (CONUS) data uses the NAD83. NAD27 Coordinates are transformed automatically.
The NED (Alaska) data uses the NAD27. NAD83 Coordinates are transformed automatically.
The SRTM data uses the WGS84. NAD83 and NAD27 Coordinates are transformed automatically.
In the Pathloss program click "Configure" – "Terrain Database" and depending on the dataset select either "NED CONUS", "NED Alaska" or "SRTM" from the drop down list. Click Setup Primary (or Secondary depending on your selection). Click the file button and browse to find and load the file with the BIL extension. The program is now setup to use the selected BIL file.
