Downloaded USGS NED Data Files
Q: I downloaded NED data from the USGS "Seamless Data Distribution" site. But TAP doesn't recognize the files. What is the problem?
A: TAP6 can read the NED (National Elevation Dataset) elevations in the .BIL format.
First, be sure you are downloading the .BIL (band interleaved) format, since the USGS site has other data formats available.
After selecting the area you want to download on the USGS site:
Click the "Modify Data Request" button.
Then change the Data Format to "BIL_16INT"
Click the "Save Changes & Return" button
Click the "Download" button to start the data download.
Unzip the file you download into a folder where you want to use the data with TAP, such as the DATA folder where TAP is installed. For TAP to use the data, it must be indexed.
If you have a problem indexing the data files, the following may be helpful:
You should have at least the following files for the .BIL download:
.BIL This is the actual data file, almost always the largest
.BLW The "World" file that relates the elevation values in the .BIL file to where they are located in the world
.HDR More header information about the data
.PRJ Projection information about the data (This file may need editing after downloading.)
If all four of these are not there, TAP doesn't have all the information it needs to use the data, and assumes it is not really a .BIL file. (All the other metadata and shapefiles are interesting information used by other software or to document the source of the data, but all TAP needs are those basic four files.)
Try the download again (the USGS site is great when it works, but occasionally I have had problems and needed to download an area again. Not often, but it has happened.)
Give it another try, and assuming you get all four files described above, if you still have a problem, and you have a current Support Subscription, zip the files together and email them to me so I can see what else might be going on. (On a couple of occasions, the files I got from a download don't match the USGS documented format - again, not often, but enough to make me a little suspicious).
A final option - if you want to avoid the hassle, you can email Curt (mailto:curt.alway@softwright.com) for pricing on purchasing the data from us.
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