SDTS Files

The DEM Reader will directly read DEMs in the original format, but will not read the new SDTS files. As result, a special converter is included with the DEM Reader that will convert SDTS files to the original format. Here are instructions for unpacking and converting these files.

Decompressing SDTS Files. In the original DEM format, each quadrangle consisted of one file. In the SDTS format, each quadrangle consists of many files, each containing part of the DEM data. For this reason, some SDTS files are archived in a Unix style file format called "TAR" files. To unpack these files, you will need a copy of Winzip, which is available at the following web site: http://www.winzip.com/

Here are the steps required to uncompress a SDTS file:

1. Make Sure The Extension Is Right. Before you decompress the files, check the extension of your file. If the extension is “ZIP”, the file is a standard zip file and you don’t need to take any action. However, if the extension is missing, it is probably a Unix format file and you will need to add the extension “GZ” before Winzip will recognize the file and decompress it.

2. Decompressing. If Winzip is correctly installed on your computer, you should be able to double click on the GZ or Zip file and the program will begin to decompress it. If the file is a normal zip file, it will contain several files with the extension DDF.

If you are decompressing a Unix-style, Winzip will be confused and ask you for an extension. If it does, use the extension "TAR. This will enable WinZip to understand that it is a TAR format archive file and it will automatically extract all the files inside. You should now see several files with the extension DDF.

3. Converting SDTS Files. When you have finished decompressing and extracting the files, the directory should contain about a dozen files that look something like this:

1109CATD.DDF 1109CATS.DDF 1109CEL0.DDF 1109DDDF.DDF

The next step is to convert these files to a single DEM file. You do this by running SDSTCon, which can be found in the “Compass Folder” in your “Start Menu” under “Programs.”

Once the program is running, select the “File|Convert SDTS to DEM” option from the menu bar.

Selecting An SDTS File. You will first be prompted to select an SDTS file that contains the data you wish to convert. Generally, this will be an SDTS “CEL0” file. For example, a typical filename could be “6221CEL0.DDF”. The program will only show you files that have the format of “????CEL?.DDF where the question mark can be any character. If for some reason, the file you will be converting has a different name, you can change the “File Type” at the bottom of the window to show more files.

Selecting A DEM File. Next you will be prompted to enter the name of DEM files you want the data written to. As soon as the file is selected, the program will begin converting the data. As the data is processed, the bar at the bottom of the window will indicate the progress. While the file is processed, information about DEM information will be displayed in the center window.

Refer to the SDTS Converter Help File for more detailed information about the conversion process.