MGD77CONVERT(1) Generic Mapping Tools MGD77CONVERT(1)NAMEmgd77convert - Translate between different formats of MGD77 files
SYNOPSISmgd77convert NGDC-ids -Fa|c|m|t -T[+]a|b|m|t [ -L[w][e][+] ] [ -V ] [
-4 ]
DESCRIPTIONmgd77convert 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.
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). The ".mgd77" or
".nc" extensions will automatically be appended, if needed (use
-I to ignore certain 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].
-F 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), revised
MGD77T (tab-delimited; with 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 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), revised
MGD77T (tab-delimited; with 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 cur‐
rent directory. Prepend + to override this policy.
OPTIONS
No space between the option flag and the associated arguments.
-L 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 Selects verbose mode, which will send progress reports to stderr
[Default runs "silently"].
-4 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 1 fTesla, 1 nGal, and 0.01 mm, respec‐
tively. This option activates such storage [Default uses 2-byte
integers].
EXAMPLES
To convert 01010047.mgd77 and 01010008.mgd77 to new netCDF .nc files,
and capture all verification messages, try
mgd77convert 01010047 01010008 -Fa -Tc -V -Lew+ > log.lis
To convert 01010047.nc back to MGD77 ASCII and make sure it is identi‐
cal to the original file, try (Bourne shell syntax)
orig=`mgd77path 01010047 -Ic`
mgd77convert 01010047 -Fc -Ta -V
diff $orig 01010047.mgd77
To convert 01010047.nc to a plain ASCII table for manual editing, over‐
writing any existing table, try
mgd77convert 01010047 -Fc -T+t -V
To recover the original NGDC MGD77 version of 01020051.nc and ignore
any E77 corrections, use
mgd77convert 01020051 -FC -Ta -V
FILE FORMATSmgd77convert handles four different formats. (1) The MGD77 ASCII tables
are the conventional standard for distribution of underway geophysical
data to and from the NGDC data center. Normally, only the ship-opera‐
tions people and the cruise PI might be involved in making an MGD77
ASCII file for transmission to NGDC; users are more interested in read‐
ing such files. (2) The MGD77+ netCDF format was developed to fascili‐
tate the use of MGD77 data by scientists. It contains all the informa‐
tion 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) NGDC
has now started to use a new tab-delimited version of the MGD77 data,
called MGD77T. In addition to all the info in old MGD77 files it con‐
tains a few more quality flags for grav, mag, and bathymetry. (4) The
plain ASCII tab-separated dump is available for users who need to manu‐
ally 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. It differs from format MGD77T
in that missing items are written as NaNs.
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 ALSOmgd77manage(1), mgd77list(1), mgd77sample(1), mgd77track(1)x2sys_init(1)REFERENCES
Wessel, P., and W. H. F. Smith, 2015, The Generic Mapping Tools (GMT)
version 4.5.14 Technical Reference & Cookbook, SOEST/NOAA.
Wessel, P., and W. H. F. Smith, 1998, New, Improved Version of Generic
Mapping Tools Released, EOS Trans., AGU, 79 (47), p. 579.
Wessel, P., and W. H. F. Smith, 1995, New Version of the Generic Map‐
ping Tools Released, EOS Trans., AGU, 76 (33), p. 329.
Wessel, P., and W. H. F. Smith, 1995, New Version of the Generic Map‐
ping Tools Released, http://www.agu.org/eos_elec/95154e.html, Copyright
1995 by the American Geophysical Union.
Wessel, P., and W. H. F. Smith, 1991, Free Software Helps Map and Dis‐
play Data, EOS Trans., AGU, 72 (41), p. 441.
ncBrowse, see http://www.epic.noaa.gov/java/ncBrowse/
ncView, see http://meteora.ucsd.edu/~pierce/ncview_home_page.html
The Marine Geophysical Data Exchange Format - "MGD77", see
http://www.ngdc.noaa.gov/mgg/dat/geodas/docs/mgd77.txt
GMT 4.5.14 1 Nov 2015 MGD77CONVERT(1)
