NAME

       mgd77convert - Convert MGD77 data to other file formats

SYNOPSIS

       mgd77convert NGDC-ids  -Fa|c|m |t
        -T[+]a|c|m|t [  -C ] [  -D ] [  -L[w][e][+] ] [  -V[level] ]

       Note: No space is allowed between the option flag and the associated arguments.

DESCRIPTION

       mgd77convert reads versions of MGD77 files and writes the same data in (probably) another format to a new
       file in the current directory.  Both pre- and post-Y2K MGD77 formats can be processed.

REQUIRED ARGUMENTS

       NGDC-ids
              Can be one or more of five kinds of specifiers:

              1. 8-character NGDC IDs, e.g., 01010083, JA010010etc., etc.

              2. 2-character agency codes which will return all cruises from each agency.

              3. 4-character <agency><vessel> codes, which will return all cruises from those vessels.

              4. =list, where list is a table with NGDC IDs, one per line.

              5. If nothing is specified we return all cruises in the data base.

              (See  mgd77info  -L for agency and vessel codes). If no file extension is given then we search for
              files with one of the four known extensions.  The search  order  (and  the  extensions)  tried  is
              MGD77+  (“.nc”),  MGD77T  (“.m77t”),  MGD77  (“.mgd77”  ) and plain text file (“.dat”).  Use -I to
              ignore one or more of these file types). Cruise files will be looked  for  first  in  the  current
              directory  and  second in all directories listed in $MGD77_HOME/mgd77_paths.txt [If $MGD77_HOME is
              not set it will default to $GMT_SHAREDIR/mgd77].

       -Fa|c|m |t
              Specifies the format of the input (From) files. Choose from a for standard MGD77 ASCII table (with
              extension .mgd77), c for the new MGD77+ netCDF format (with extension .nc), m for the  new  MGD77T
              format  (extension  .m77t) and t for a plain ASCII tab-separated table dump (with extension .dat).
              Use -FC to recover the original MGD77 setting from the MGD77+ file [Default  will  apply  any  E77
              corrections encoded in the file].

       -T[+]a|c|m |t
              Specifies  the format of the output (To) files. Choose from a for standard MGD77 ASCII table (with
              extension .mgd77), c for the new MGD77+ netCDF format (with extension .nc), m for the  new  MGD77T
              format  (extension  .m77t) and t for a plain ASCII tab-separated table dump (with extension .dat).
              We will refuse to create the file(s) if they already exist in the current directory. Prepend +  to
              override this policy.

OPTIONAL ARGUMENTS

       -C     Convert from NGDC two-file data sets *.h77, *.a77 to single file *.mgd77. No other options (except
              -V) are allowed. Give one or more names of *.h77 files, *.a77 files, or just the file prefixes.

       -D     By default, the storage types used in a MGD77+ netCDF file greatly exceed the precision imposed by
              the  ASCII  MGD77  format.  However,  for the five items faa, eot, mag, diur and msd we use 2-byte
              integers with implied precisions of 0.1 mGal, 0.1 nTesla, and 1 m as in the MGD77  format.  It  is
              possible  that  at  some point these items will need to be stored as 4-byte ints which would allow
              precisions of 10 fTesla, 1 nGal, and 0.01 mm, respectively. This  option  activates  such  storage
              [Default uses 2-byte integers].

       -L[w][e][+]
              Set  the  level of verification reporting [none] and where to send such reports [stderr]. Append a
              combination of w for warnings, e for errors, and + to send such log information to stdout.

       -V[level] (more …)
              Select verbosity level [c].

       -^ or just -
              Print a short message about the syntax of the command, then exits (NOTE: on Windows just use -).

       -+ or just +
              Print an extensive usage (help) message, including the explanation of any  module-specific  option
              (but not the GMT common options), then exits.

       -? or no arguments
              Print a complete usage (help) message, including the explanation of all options, then exits.

EXAMPLES

       To convert a large set of a77,h77 pairs to proper mgd77 files, try

              gmt mgd77convert -C *.h77

       To  convert  01010047.mgd77  and  01010008.mgd77  to  new  netCDF .nc files, and capture all verification
       messages, try

              gmt mgd77convert 01010047 01010008 -Fa -Tc -V -Lew+ > log.lis

       To convert 01010047.nc back to MGD77 ASCII and make sure it  is  identical  to  the  original  file,  try
       (Bourne shell syntax)

              orig=`gmt mgd77path 01010047 -Ic`
              gmt mgd77convert 01010047 -Fc -Ta -V
              diff $orig 01010047.mgd77

       To convert 01010047.nc to a plain ASCII table for manual editing, overwriting any existing table, try

              gmt mgd77convert 01010047 -Fc -T+t -V

       To recover the original NGDC MGD77 version of 01020051.nc and ignore any E77 corrections, use

              gmt mgd77convert 01020051 -FC -Ta -V

FILE FORMATS

       mgd77convert  handles  four  different  formats.   (1)  NGDC has now started to use the new tab-delimited
       version of the MGD77 data format, called MGD77T.  In addition to all the  info  in  old  MGD77  files  it
       contains  a  few  more  quality  flags  for  grav, mag, and bathymetry.  (2) The MGD77+ netCDF format was
       developed to facilitate the use of MGD77 data by scientists. It  contains  all  the  information  of  the
       original  MGD77  file and if you convert back and forth you end up with the original. However, file sizes
       are typically ~30% of the original ASCII format and is much faster to operate on.  (3)  The  MGD77  ASCII
       tables  are  the  traditional standard for distribution of underway geophysical data to and from the NGDC
       data center, now superseded by MGD77T.  Normally, only the ship-operations people and the cruise PI might
       be involved in making an MGD77 ASCII file for transmission to NGDC; users are more interested in  reading
       such  files.  (4) The plain ASCII tab-separated dump is available for users who need to manually edit the
       content of a MGD77 file.  This is usually easier to do when the columns are tab-separated than when  they
       are all crunched together in the MGD77 punch-card format.

OTHER TOOLS

       The  MGD77+  netCDF  files are CF-1.0 and COARDS compliant and can be examined with general-purpose tools
       such as ncBrowse and ncView.

SEE ALSO

       mgd77manage, mgd77list, mgd77info, mgd77track x2sys_init

REFERENCES

       ncBrowse,           see           http://www.epic.noaa.gov/java/ncBrowse/           ncView,           see
       http://meteora.ucsd.edu/~pierce/ncview_home_page/  The Marine Geophysical Data Exchange Format - “MGD77”,
       see http://www.ngdc.noaa.gov/mgg/dat/geodas/docs/mgd77.txt

COPYRIGHT

       2018, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe

5.4.3                                             Jan 03, 2018                                MGD77CONVERT(1gmt)