SDTS2DLG(1)						      General Commands Manual						       SDTS2DLG(1)

NAME

       sdts2dlg - Convert a USGS SDTS DLG to a DLG in the `optional' format.

SYNOPSIS

       sdts2dlg [-L] | [sdts_dlg_file.ddf [output_file_name]]

DESCRIPTION

       The  U.S. Geological Survey (USGS) provides sites on the Internet with a lot of Digital Line Graph (DLG) data.  Depending on the resolution
       of the data, it may be available in one of at least two different formats:  the `optional' DLG format, or the Spatial Data Transfer  System
       (SDTS) format.  The 24K DLG data (which are also called 7.5-minute DLG data) are only available for free download in the SDTS format.

       The  drawmap program can read files in SDTS format; but the SDTS information comes in the form of archives, each of which contains numerous
       files.  It may sometimes be more efficient, and perhaps simpler, to store the data in the `optional' format.  Sdts2dlg is  a  program  that
       converts each SDTS archive into a single optional-format DLG file.  Currently sdts2dlg only works with 24K and 100K DLG data.

       If you invoke the program with the "-L" argument, it will print some license information and exit.  In normal use, the first argument is an
       SDTS file name.

       Each SDTS DLG archive should contain one or more files with names of the form ????LE@@.DDF, where the '?'  symbol  stands  for  any  single
       character,  and	the  '@'  symbol  stands for any single digit.	If you provide a single such file as an argument, sdts2dlg will produce an
       optional-format DLG file, based on the given SDTS file and the other files in the SDTS archive.	(When you unpack the  SDTS  archives,  you
       can  change  all of the resulting file names to all lower case and/or compress all of the files with the gzip program.  If you are going to
       change to lower case, change all of the files.  If you are going to compress the files, compress all of them.)

       The USGS takes each 1-degree-square block of latitude and longitude, and divides  it  into  an  eight-by-eight  grid  of  7.5-minute-square
       `quads'.   The rows of this grid are labeled 'a' to 'h' from bottom to top, and the columns are labeled `1' through `8' from right to left.
       Each quad is then referred to by a name of the form `AABBBCD', where `AA' is the latitude of the southeast corner of  the  1-degree  block,
       `BBB' is the longitude of the southeast corner, and `C' and `D' represent the corresponding row and column labels.  If you don't specify an
       output file name, the output file produced by sdts2dlg will have the form `AABBBCD.dlg'.  For 100K DLG files, each of which generally  cov-
       ers 16 quads, this naming is also used, with the `C' and `D' code being the same as for the quad with the same southeast corner as the 100K
       DLG data.  If you specify an output file name, then your name will be used instead.

LIMITATIONS

       Sdts2dlg attempts to recreate the original DLG-3 file, as it was before conversion to SDTS.  Node entries include line lists, but  no  area
       lists.	Area  entries  include	line  lists,  no  node	lists,	and no area coordinate lists.  Line entries include line coordinate lists.
       Attributes are included as major-minor pairs.

       Try as it might, though, sdts2dlg is going to produce files that differ from the originals.  In the Node entries,  for  example,  the  line
       lists have no preferred ordering, and the output from sdts2dlg is unlikely to reproduce the ordering of the original DLG file.  In the Area
       entries, the line lists do have a specified ordering, but there is no rule for choosing which line to start  each  list	with.	Thus,  the
       lists  are  unlikely  to  be exact duplicates of the original file.  Neither of these differences should be a problem.  The lists are still
       valid, even if they are not identical to the originals.

       For the universe polygon (which completely surrounds the data coverage area) the Universal Transverse Mercator  (UTM)  coordinates  of  its
       representative  point are likely to be different from the originals.  The SDTS files do not appear to encode this particular representative
       point, so sdts2dlg inserts the coordinates of the southwest corner of the map area.

       Some floating-point numbers will have a different format from their original USGS versions.  The USGS files normally put the first signifi-
       cant  digit after the decimal point, while sdts2dlg puts it in front of the decimal point.  The actual numeric values are the same, but the
       format differs.

       There are two fields in the header that don't always show up in existing optional-format files, although  the  specification  allows  them:
       the horizontal datum and the vertical datum.  These are too useful to leave out, so sdts2dlg includes them.

       Finally,  there	may  be  data  discrepancies due to errors in the program.  Errors are a distinct possibility when it comes to attributes.
       There are many different kinds of possible attributes, and I have not yet found adequate test data for some of them.

SEE ALSO

       drawmap(1), sdts2dem(1)

								   Jul 24, 2001 						       SDTS2DLG(1)