Adding and Removing Record Delimiters on USGS Data.

Adding Delimiters

DEM, DLG, and LULC data obtained from USGS do not contain record delimiters. In some cases you will need to add them before using display programs. Once you down load the files you can add delimiters using the following UNIX command lines:

      1:250,000-scale Digital Elevation Models (DEM):
          dd if=inputfilename of=outputfilename ibs=4096 cbs=1024 conv=unblock 

      Digital Line Graph (DLG) data:
         Optional Format: 
          dd if=inputfilename of=outputfilename ibs=8000 cbs=80 conv=unblock 
         Standard Format: 
          dd if=inputfilename of=outputfilename ibs=8064 cbs=144 conv=unblock 
         SDTS Format:
          not applicable

      Land Use and Land Cover (LULC) data
          dd if=inputfilename of=outputfilename ibs=8000 cbs=80 conv=unblock
    

Removing Delimiters

When Arc/Info, and possibly other GIS software, creates DEM files it automatically adds record delimiters. Flyby, and possibly other applications, require the fixed record format DEM's provided by USGS. The following commands will remove record delimiters from DEM, DLG, and LULC data files. The DEM conversion has been tested and works. The others have yet to be used but it is assumed they will also work. Remove delimiters using the following UNIX command lines:

      1:250,000-scale Digital Elevation Models (DEM):
          dd if=inputfilename of=outputfilename ibs=4096 cbs=1024 conv=block 

      Digital Line Graph (DLG) data:
         Optional Format: 
          dd if=inputfilename of=outputfilename ibs=8000 cbs=80 conv=block 
         Standard Format: 
          dd if=inputfilename of=outputfilename ibs=8064 cbs=144 conv=block 
         SDTS Format:
          not applicable

      Land Use and Land Cover (LULC) data
          dd if=inputfilename of=outputfilename ibs=8000 cbs=80 conv=block
    

Original USGS delimiter information