Last updated 4/4/2000. DAS.
NGSDEM99 is a 1 x 1 arcsecond Digital Elevation Model (DEM) of the Northwest
United States, covering the region 39 - 49N latitude, and 234 - 256E longitude.
It was built at the National Geodetic Survey (NGS) in July 1999. The
primary data sets used were a combination of DEM data (10 meter and 30 meter)
from the United States Geological Survey
DTED level 1 data from the National Imagery and Mapping Agency
(NIMA). After extensive cleansing these
data were re-gridded into the NGSDEM99 data set.
- How big is NGSDEM99?
- Although great pains were made to keep the disk space to a minimum
(i.e. storing the data in a 2-byte integer format), the total disk space to
hold NGSDEM99 is 6.3 Gb.
NGSDEM99 is stored in 250 files, each spanning 1 x 1 degree
areas, and each being 26 Mb.
- Where can I get my hands on NGSDEM99?
- At the moment, in general, you can't. Because we have used NIMA DTED level 1
data in NGSDEM99, we may only distribute NGSDEM99 to a very limited set of persons.
However, we have plans for the production of a new DEM, NGSDEM99B which
will use USGS 3 arcsecond DEM data rather than NIMA DTED level 1 data,
which will allow us to freely distribute NGSDEM99B to the general public.
We plan for NGSDEM99B to be available as soon as we possible, but the
priority for this is currently low.
The only agencies authorized for release of the original NGSDEM99 files
are United States Department of Defense agencies. Additionally, other
United States Government agencies may request the data. E-mail Dr. Dru Smith
firstname.lastname@example.org for details.
- Where can I find more information on NGSDEM99?
- We have written a paper, but it is not yet published. It may be
referenced however as: Smith, D.A. and D.R. Roman, 2000: A new
high-resolution DEM for the Northwest United States, accepted for publication
in Surveying and Land Information Systems.
- I just want the RAW USGS DEM data. Where may I find that?
- You can find the RAW USGS 10 and 30 meter DEM data, in SDTS format,
on their web site. Click
here to go to it.
- What about the USGS NED data set? Is that the same thing as NGSDEM99?
- The USGS NED (National Elevation Dataset)
begins with nearly the same data
as NGSDEM99, but there are a few key differences between NGSDEM99 and NED:
- There is no NIMA DTED Level 1 data in the NED files
- The NED covers all of the USA and Alaska and is continually updated
- There has been no published list of blunders which were fixed for the NED (the blunder list is
an appendix of the Smith and Roman (2000) paper, above).
- The NED was built using "mean profile filtering", for various reasons. The NGSDEM99 data
has no filtering, aside from blunder correction.
- The NGSDEM99 is freely available with special permission from NIMA. The NED is sold at $1 per
quad (plus other charges).