The files were downloaded, decompressed, logged into the VICAR image processing system. The size of the files are 1201 lines by 1201 samples. The imagery was reduced to 258x258 for the Vistapro small format, 514x514 for the large format, and 1026x1026 for the huge format. The files were then read into Vistapro with the Load Binary option, and then saved with the Save DEM option. The resulting files were then compressed with PKZIP, a readily available shareware DOS compression utility. Almost all decompression utilities can handle PKZIP files as it is a "de facto" compression standard.
Warning! These files, especially
the large and huge formats, are very big. They
will take quite a bit of time to download. The sizes are listed on the
download/selection pages, the text only version lists the compressed sizes
only. The graphics version lists both the compressed size as well as the
decompressed size. In total, the compressed size of the small
files add up to 905,592 bytes, decompressed they total 1,512,994 bytes.
The large files total 2,780,689 bytes compressed and 5,202,739
bytes decompressed. The huge total a whopping 8,161,857 bytes
compressed and 17,633,881 byted decompressed. These files will be placed on
the next version of the CASDE CD-ROM, so you may not want to download the
entire state at this time.
If 1° x 1° coverage is too small for you, you can combine the files
to cover a larger area. For example, before loading any files into Vistapro,
set the DEM size to large. Then load in one of the
small files. The program will recognize the file as being
258x258 and ask you if you want to place the file manually or automatically
into a 4x4 grid. Choose manually as it does not seem to place them
correctly in the automatic mode. Then load the other three quadrants, again
placing them manually. In this manner, you can create a 2° x 2° DEM
file for use by Vistapro. Be forwarned that processing will not be as fast
as using the smaller files, so this rendering in this manner may be an
overnight process for your students. Using this technique, you can "mix
and match" to make as big of a mosaic as you want. The maximum is using the
mega DEM size with the small files. This yields
an 8° x 8° Vistapro DEM file. Keep in mind that the State of
Nebraska is only 3° North and South by 9° East and West. Not an
optimal ratio for this method, but usable in any case.
This is version 1.0 of these pages. Please send your feedback to me via
e-mail at steven@dial.jpl.nasa.gov so that I can incorporate your
suggestions into the next version. Thank you, and happy computing.
(These notes just thrown together. Page not checked for proper
spelling and grammer.)
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