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| GeoCommunity Mailing List |
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| Mailing List Archives |
| Subject: | GISList: Attention S/W Developers & Vendors Supporting SDTS Raster Profile |
| Date: |
08/29/2001 01:55:56 PM |
| From: |
Hylan L Beydler |
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|
Attention Software Developers and Vendors Supporting SDTS Raster Profil=
e,
If your software can currently process USGS SDTS DEMS, then it may fail=
after October 1, 2001. A non-compliant profile identifier was used in =
the
USGS SDTS DEMS that were released for vendor software testing, and thos=
e
subsequently released to the public at the GeoCommunity GIS Data Depot.=
If
you coded to our example, and not the FGDC Raster Profile standard, you=
unknowingly perpetuated our non-compliant profile identifier string. T=
he
USGS used "SRPE: RASTER PROFILE and EXTENSIONS" in the Identification
module (file xxxxIDEN.DDF). The FGDC compliant value is "SRPE: SDTS RAS=
TER
PROFILE and EXTENSIONS".
The compliant USGS SDTS DEMS will be available from the GIS Data Depot =
to
the public circa October 1, 2001. Sample test datasets are at
ftp://sdts.er.usgs.gov/pub/sdts/datasets/raster/dem. The FGDC Raster
Profile is at http://www.fgdc.gov/standards/documents/standards/sdts_pt=
5/.
The USGS sincerely appreciates your efforts to promote FGDC standards. =
We
encourage you to modify, retest, and announce to your users about the n=
eed
for the software change. If you need further information from the USGS,=
please contact the SDTS Task Force at sdts@usgs.gov.
More Details on the Legacy of the USGS SDTS DEMS
Table 1: Summary of Profile Identifier Variants and SDTS DEM
Characteristics
a) Draft Identifier "SDTS RASTER PROFILE"
Available from USGS EDC GeoData site 1998?6/2001. Contain geopositi=
onal
error. Only use integer data type. Approximately 15 million download=
s.
b) USGS typo "SRPE: RASTER PROFILE and EXTENSIONS"
Available from GIS Data Depot 7/2001?9/2001. Contain incorrect profi=
le
identifier. Includes decimeter DEMs with binary floating point
elevation values. Approximately 50,000 downloads.
c) FGDC Profile Identifier "SRPE: SDTS RASTER PROFILE and EXTENSIONS"=
Available from GIS Data Depot beginning 10/2001 contain correct prof=
ile
identifier. Note in README explains which errors are fixed, so custo=
mers
know when they have corrected data.
In 1997, the 7.5-minute DEM holdings were converted en mass to the draf=
t
form of the SDTS Raster Profile (Table 1a). These DEMs were distribute=
d
free from the EDC GeoData Web/FTP site from 1998 through June 2001. Th=
ese
SDTS DEMs contain the draft profile identifier of "SDTS Raster Profile"=
. In
providing technical support to our data customers, we discovered a
geopositional error that was introduced during the conversion. The
elevation values were not affected, but the post position could be off =
as
much as 30 meters horizontally. This affected some applications, but n=
ot
all. There were approximately 15 million SDTS DEMs downloaded.
In February 2001, the 7.5-minute DEM holdings were converted en mass to=
the
ratified FGDC SDTS Raster Profile (Table 1b). Changes included: 1) A n=
ew
profile identifier: 2) a new elevation data type of binary floating poi=
nt*:
3) a corrected geopositional conversion: and, 4) improved metadata
regarding data quality. These DEMS are being distributed from the
GeoCommunity GIS Data Depot site as of July 2001.
In August 2001, the 7.5-minute DEM holdings will be converted en mass u=
sing
the correct profile identifier (Table 1c). These DEMs will be distribu=
ted
from the GeoCommunity GIS Data Depot site circa October 2001. Check the=
web
site for the current status.
* The DEM product changed to decimal units for the elevation values so =
most
DEMs made after 1999 use a data type of floating point (i.e. 810.25) ra=
ther
than the previous integer type (i.e. 850).
Additionally, we provide space on our web site (
http://mcmcweb.er.usgs.gov/sdts/implement-priv.html) for developers and=
vendors who support SDTS. If you wish to add your product information =
to
our site please email your request to sdts@usgs.gov.
Thank you,
Hylan
Hylan Beydler, USGS
National Mapping Program Standards, SDTS Task Force
1400 Independence Road
Rolla, MO 65401=
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