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A message to SDTS List Explaining the USGS-GeoCommunity Agreement

This message was distributed to the SDTS email-based discussion list in response to a thread posted by a concerned member of the GIS Community. This message explains why the USGS is now serving DEM data via The GISDataDepot
 

Re: errors since 1:24,000-Scale DEM SDTS file were move to http://www.gisdatadepot.com/

The U.S. Geological Survey (USGS) has entered into an agreement with the
GeoCommunity to serve updated, SDTS format, Digital Elevation Models (DEMs)
through the GIS Data Depot at http://www.gisdatadepot.com for no charge.
The 7.5' SDTS DEM data are also available for purchase via premium (fast)
download and on CD-ROM from GeoCommunity.

USGS distribution of SDTS DEMs through Earth Explorer has been
discontinued.  A link to the GIS Data Depot from the USGS Geographic Data
Download Web site, http://edcwww.cr.usgs.gov/doc/edchome/ndcdb/ndcdb.html ,
provides direct access to SDTS DEMs for customers coming to the USGS for
these files.

The decision to provide SDTS DEMs through the GIS Data Depot is consistent
with the USGS goal of making more public domain data available at no charge
while enabling the private sector to have a greater role in the
distribution of USGS data.  SDTS DEMs placed on media in response to
customer orders will be sold by the GeoCommunity at a price less than the
USGS currently charges.

The GeoCommunity will continue to receive SDTS versions of the DEMs as they
are made available by the USGS.  Native format DEMs are still available for
sale from USGS on various media and via ftp.  Other websites will also be
hosting the SDTS DEMs in the future.

In addition to correcting positional errors, the draft SDTS Raster Profile
was replaced during the conversion process.  Some slight differences exist
between the two standards which may (if hard coded in GIS software from the
draft standard) cause application failures when using with the new SDTS
DEMs.  Below is a list of some of the differences.  We are currently
investigating an initial work around.

A. The differences between pre and post jan2001SDTS DEMs:

  1)The Profile Identification PRID subfield in the xxxxIDEN.DDF:
      pre  jan2001 have PRID of "SDTS RASTER PROFILE"
      post jan2001 have PRID of "SRPE: RASTER PROFILE and EXTENSIONS"

2)Data type for CEL0 values of SDTS DEMs:
     pre jan2001 z-units were in feet or meters .....data type BI16.
     post jan2001 z-units can be feet, meters or decimal meters....
                       data type can be BI16 (feet or meters)
                       or BFP32 (for decimal meter)

B. The Sol Katz sdts2dem/sdtsedem .exe's does not work on the SDTS decimal
meter DEMs.
     Also, the sdtsedem/sdts2dem .exe's (versions .011 and .012) have map
boundary info in the pre-2001 SDTS DEMs, but incorrect/missing boundary
numbers in the post-2001 SDTS DEMS .... along with incorrect z-values...

C. ArcView 3.2/ERDAS Imagine 8.4 does not recognize PRID of SRPE: RASTER
PROFILE and EXTENSIONS as a
     valid SDTS Profile. There is no problem with ArcInfo8 and
ArcView8...ArcToolbox works OK.

D. DLGv32 does not display SDTS decimal meter DEMs correctly...color
stretch/z values incorrect.

E.  Software vendors that support the new SDTS DEMs with z-units of feet,
meters, and decimal meters:
     ArcInfo 8, ArcView 8 via ArcToolbox.
     ArcView3.2 (requires editing of xxxxIDEN.DDF----contact me if you would
like to try the test work-around)
     ERDAS Imagine 8.4 (requires editing of xxxxIDEN.DDF---contact me if you
would like to try the test work-around )
     FME
     3DEM
     MicroDEM

Please monitor the following websites for updates regarding the new
changes.

http://edcwww.cr.usgs.gov/doc/edchome/ndcdb/ndcdb.html
and
http://mcmcweb.er.usgs.gov/sdts/

We appreciate your comments.  If you have additional questions, please
contact us again.

Sincerely,
Elizabeth McCartney
USGS Earth Science Information Center


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