sdts2dem: a Translator for SDTS DEM Files

Version 0.018: April 29, 2002

The sdts2dem program translates USGS DEM files from SDTS format to "native" format.
It is in the public domain and may be freely redistributed.

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Browse the program source code, which includes the revision history: sdts2dem.c
Download a self-contained executable file for Windows: sdts2dem.exe
Download the source package for Unix or Windows, including the f123 library: f123.tar.gz or f123.zip

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History

The United States Geological Survey (USGS) produces digitally-encoded terrain data in the form of regular grids called "digital elevation models", or DEM files. Several different file formats have been used, culminating in the incredibly complex Spatial Data Transfer Standard, or SDTS.

The adoption of SDTS was a giant step backwards. While previous DEM files could be read by relatively simple programs, SDTS file are difficult to read even with the help of a large external library (which may or may not be available in the language of choice). The late Sol Katz, of the Bureau of Land Management, wrote the sdts2dem program to read SDTS DEM files and produce files in the simpler "native" format. This translation program was a great boon to those who just wanted to read the data without fighting a complex encoding.

In the summer of 2001, changes in the use of SDTS format by the USGS improved the data quality but rendered the sdts2dem program nearly useless. Having a need to convert the new files, I modified the program to handle the format changes and published the new version on the web. There turned out to be a great demand for it and I seem to have become its ongoing caretaker.

The revised sdts2dem program:

• converts SDTS DEM files to "native" format
• handles both pre- and post- Y2001 SDTS files
• handles fixed- or floating-point elevation values
• handles large grids such as 10x10 meter quadrangles
• fixes several bugs present in earlier versions

For a more detailed list of recent changes, see the source code.

Usage

Here are some guidelines for using sdts2dem successfully on a Windows system.

• Each .tar.gz dataset collects several *.DDF files representing just one "SDTS transfer" -- a single elevation grid. Unpack each transfer in its own directory, for the file names in different transfers may not be unique.
• If you unpack using WinZip, be sure that the "TAR file smart CR/LF conversion" box is NOT checked on the Options/Configuration/Miscellaneous screen.
• To run sdts2dem by clicking its icon, put it in the same directory as the .DDF files.
• If sdts2dem exits unexpectedly, open a command window and run it there so that you can see any error messages. (Make the directory containing the DDF files your current directory.)
• The program can accept command-line options, but if you just run it with none it will print a usage message and prompt you for what it needs.

Data

In the summer of 2001, the USGS suddenly halted its free distribution of SDTS DEM files via FTP. The distribution function was assumed to some extent by commercial concerns, and IntraSearch MapMart has a nice map-based interface that provides up to ten free quadrangles per batch in exchange for personal information.

It appears, though, that production of SDTS DEM files has halted. Current USGS efforts focus on the National Elevation Dataset, which provides seamless coverage using different file formats.

Related Links

MapMart DEM download page

DEM Standards (for the native format written by sdts2dem)
USGS SDTS site
History of SDTS format changes
SDTS Standards

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Gregg Townsend
Department of Computer Science
The University of Arizona

gmt@cs.arizona.edu