Provided by: gmt-common_5.4.3+dfsg-1_all 
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