#!/usr/bin/perl

# Used to convert simple long by lat data into NMEA format.
# Data available from:
#   (URL: http://crusty.er.usgs.gov/coast/getcoast.html )

$Time = 0;

while (<>) {
   if (/^#/) {
      $NMEA = "GPGGA,999999,0000.0000,N,00000.0000,W,3,0,0.0,0,M,,,,";
      print "\$" . $NMEA . "*" . &NMEAChecksum($NMEA) . "\n";
      next;
   }

   s/^(-{0,1})(\d+)(\.\d+)\s+(-{0,1})(\d+)(\.\d+)//;

   $LatMin = $6 * 60;
   $LongMin = $3 * 60;

   $NMEA = sprintf("GPGGA,%06d,%02d%07.4f,%s".
      ",%03d%07.4f,%s,1,3,0.0,0,M,,,,",
      $Time, 
      $5, $LatMin,  $4 eq "-" ? "S" : "N",
      $2, $LongMin, $1 eq "-" ? "W" : "E"
   );

   print "\$" . $NMEA . "*" . &NMEAChecksum($NMEA) . "\n";

   $Time++;
}

sub NMEAChecksum {
   local ($Str) = @_;
   local ($CS) = (0);

   while ($Str =~ s/(.)//) {
      $CS = $CS ^ unpack("%C", $1);
   }

   return sprintf("%02x", $CS);
}