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Data Problems


Errors with SDTS Data Dictionary/Schema (DDSH) files
NOTE: If you are encountering errors while reading an SDTS Data Dictionary/Schema (DDSH) file for a DLG, the file may corrupt. If you think this may be the case, please download a replacement DDSH from here, and then copy the new DDSH file over the old. (Added 11/12/2003)
Problems using SDTS DEMs available January 1-October 1?
NOTE: This information pertains to data hosted by GeoCommunity July 1-October 1, 2001. (Revised 10/11/2001)
Preliminary workaround for new SDTS DEMs
NOTE: This workaround is designed for USGS 7.5' DEMS available January 1-October 1, 2001. (Revised 10/11/2001)
Problems using SDTS 7.5' DEMs?
Prior to the change in distribution of SDTS DEMS from a USGS web site to the commercial GeoCommunity site, the USGS reprocessed all of its DEMs to fix a positional error problem introduced by the previous mass conversion (circa 1997.) Also at the same time the USGS made two other changes in the data. These changes collectively affected all of the USGS SDTS DEMs. Some GIS software may be unable to read the new SDTS DEMS because of either or both of these changes. (8/2001)
SDTS Tutorial and Translator Documents Available
March 3, 1999 -- The SDTS tutorial describes how to find, download, and unpack free SDTS data. A textual version is available for viewing and a WordTM version (SDTS.Tutorial.2003.doc) is available for downloading.

The translator document contains information about translating SDTS data to other formats. A textual version is available for viewing and a Word PerfectTM version (translators.wpd) is available for downloading.


ARC/INFO Users on Windows NT Platform
April 22, 1998 -- SDTSIMPORT command has been found to have a bug. During execution of this command, the master data dictionary cannot be found. The command will still work, but the textual information will not be attached to the spatials. If your requirements are that the textual information be attached to the spatials, you should load the master data dictionary directory into each dataset directory. Due to the fact that ARC/INFO V7.2 is nearing release, ESRI has chosen to address this bug in a subsequent version.
Decompression Software
FY 1997 -- SDTS data are archived in a non-proprietary zip format (GNU Zip). If you are planning to use an "off the shelf" decompression software like WinzipTM to unzip and untar these files be aware that many have a default conversion setting that MUST NOT be used!

For example, within WinZipTM, under "Options/Configuration", there is a checkbox that reads "TAR file smart CR/LF translation" - insure that this box is NOT checked. This will disable the default setting.


SDTS DEM Textual Error
FY 1997 -- All SDTS/DEM files prior to November 24, 1997 contain a textual error. The comment field for the VERTICAL SHIFT in the DQPA Module (DQPA.DDF file) reads as follows:
VERTICAL DATUM SHIFT: < value >. Adding this value to Horizontal coordinates will convert position to North American Vertical Datum 1988. Value is computed by averaging the shift values for the four quadrangle corners obtained from program VERTCON.
It should read as follows:
VERTICAL DATUM SHIFT: < value >. Adding this value to the elevation values will convert it to North American Vertical Datum 1988. Value is computed by averaging the shift values for the four quadrangle corners obtained from program VERTCON.
This change should also be noted in the "The Spatial Data Transfer Standard Mapping of the USGS Digital Elevation Model" documentation in Table 2.2.4.1 ID A31 on page 28, in all versions prior to 11/13/97.
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