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SpatialNews Press Release

Attention Software Developers and Vendors Supporting SDTS Raster Profile

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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 those 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. The USGS used "SRPE: RASTER PROFILE and EXTENSIONS" in the Identification module (file xxxxIDEN.DDF). The FGDC compliant value is "SRPE: SDTS RASTER 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_pt5/.

The USGS sincerely appreciates your efforts to promote FGDC standards. We encourage you to modify, retest, and announce to your users about the need 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 geopositional error. Only use integer data type. Approximately 15 million downloads.

b) USGS typo "SRPE: RASTER PROFILE and EXTENSIONS" Available from GIS Data Depot 7/2001?9/2001. Contain incorrect profile 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 profile identifier. Note in README explains which errors are fixed, so customers know when they have corrected data.

In 1997, the 7.5-minute DEM holdings were converted en mass to the draft form of the SDTS Raster Profile (Table 1a). These DEMs were distributed free from the EDC GeoData Web/FTP site from 1998 through June 2001. These 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 not 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 new profile identifier; 2) a new elevation data type of binary floating point*; 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 using the correct profile identifier (Table 1c). These DEMs will be distributed 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) rather 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

Hylan Beydler, USGS
National Mapping Program Standards, SDTS Task Force
1400 Independence Road
Rolla, MO 65401


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