asc2bin.py, experimental version of serasc2bin.py,
   presently for UHDAS files only.
   Does NOT parse ascii files from other logging systems: Use serasc2bin.py

   Usage: asc2bin.py [<options>] [-y 2001] ...
                   [-o outputdirectory] file1 [file2 ...]

      Reads ascii files written by  UHDAS and writes corresponding
      files in binary double precision.  Output file name is the
      input file name with '.rbin' appended, unless the
      --message and/or --add_extension options are used.
      By default,
      if a file of that name already exists, the corresponding
      input file will not be processed.  Use '--redo' option
      to reprocess in this case.  Use '--update' to append to
      an rbin file if it already exists.  This can be used to
      continually update an rbin file as the source file is
      being written.

      Gzipped input files are handled transparently, without
      being explicitly gunzipped; the '.gz' extension is ignored
      when generating the output filename, unless the '-a' option
      is used.

      -h or --help:     print this message and exit
      -r or --redo:     process all input files, regardless of
                           whether an output file already exists
      -u or --update:   process incrementally
      -s or --seconds:  with -u, timeout in seconds (floating point)
      -o or --outdir:   directory for output files
      -m or --message:  desired output file type (without the dot)
      -y or --yearbase: 4-digit yearbase
      -l or --log_yearbase" 4-digit yearbase (yearbase used for $UNIXD
                            during logging). defaults to same as
                            yearbase if unspecified
      -v or --verbose:  print short diagnostics
      -V or --Verbose:  echo line number and line, so we can see
                           where it chokes
      -S or --showbad:  echo line number and line when they are
                           rejected, so we can see what junk is in the
                           file
      -a or --add_extension: Add the message extension to the input
                           file name, instead of replacing the input
                           file extension
      -t or --type:     'rvdas', 'uh', 'vmdas',...  ('uh' is default)
      -c or --count:   for vmdas only:
                       VmDAS may have more than one serial message per
                       timestamp (PADCP); the timestamp comes at the
                       end of a group.  Use "--count" to specify which
                       messages to store.  The field "count" starts with
                       zero just prior to the PADCP message and decreases
                       backwards in time.
                       count switch:     outputs
                         first         (output the serial message at
                                            the beginning of the collection
                                            for the ensemble;
                                            corresponds to raw data
                                            structure nav.txy1)
                         last           (output the serial message at the
                                            end (nav.txy2)).  DEFAULT
                         all            (output all serial messages)


      NOTE: the first entry, 'u_dday', is the time of the PC doing the logging.
      For UHDAS, this is the linux clock time
      For rvdas, it is a GGA timestamp
      For VmDAS, it is the PC clock time.  Subtract sec_pc_minus_utc to get UTC


      File or message types:

         gps  GGA messages.  .gps.bin fields are logger decimal day,
                                    GGA decimal day, lon degrees,
                                    lat degrees.
                                    ??GGA message (e.g., INGGA or GPGGA)
         gga  same as gps
         spd  soundspeed     .spd.bin fields are logger decimal day,
                                    soundspeed in m/s.

         hdg  gyro heading   .hdg.bin fields are logger decimal day,
                                    heading in degrees.
                                    HEHRC or HEHDT messages are read.

         hnc  gyro heading, NO CHECKSUM
                                    .hdg.bin fields are logger decimal day,
                                    heading in degrees.
                                    HEHRC or HEHDT messages are read.

         adu  Ashtech $PASHR,ATT    .adu.bin fields are logger decimal day,
                                    ATT decimal day (GPS days in week),
                                    heading, pitch, roll, mrms, brms,
                                    reacq flag.

         pmv  POS/MV $PASHR   .pmv.bin fields are logger decimal day,
                                    GGA decimal day, heading, pitch,
                                    roll, heave, accuracy of roll,
                                    of pitch, of heading, heading flag,
                                    IMU flag.
                                    GAMS flag: (0=no aiding, 1=GPS
                                       aiding, 2 = GAMS aiding)
                                    IMU flag: (0 = no IMU; 1 = using IMU )

         rdi (various) $PRDID  .rdi.bin fields are logger decimal day,
                                    pitch, roll, heading.
                                    There is no error checking.

         psxn20 Seapath $PSXN,20   logger decimal day,
                                    quality for:  horizontal, height,
                                    heading, roll&pitch.

         psxn23 Seapath $PSXN,23   logger decimal day,
                                    roll, pitch, heading, heave

         sea                       logger decimal day,
                                    roll, pitch, heading, heave,
                                    quality for:  height,
                                    heading, roll&pitch.  (The psxn23
                                    fields preceed the psxn20 fields.)

         gps_sea                   same as gga, but with horizontal quality
                                   column from psxn20 appended

   Note: there is a slight difference in the logger decimal day for the
   Seapath gga file versus the gps_sea.  In the latter, the time stamp
   is the one from the psxn20 message, which arrives immediately after
   the gga.  Fixing this would be more trouble than it is worth.