mgd77convert(1) GMT mgd77convert(1)
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+ (a.nca), MGD77T (a.m77ta), MGD77 (a.mgd77a ) and plain
text file (a.data). 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-sep-
arated 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-sep-
arated table dump (with extension .dat). We will refuse to cre-
ate 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 pre-
fixes.
-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 a|)
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 explana-
tion 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 identi-
cal 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, over-
writing 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 sci-
entists. 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(1), mgd77list(1), mgd77info(1), mgd77track x2sys_init(1)
REFERENCES
ncBrowse, see http://www.epic.noaa.gov/java/ncBrowse/ ncView, see
http://meteora.ucsd.edu/~pierce/ncview_home_page/ The Marine Geophysi-
cal Data Exchange Format - aMGD77a, see
http://www.ngdc.noaa.gov/mgg/dat/geodas/docs/mgd77.txt
COPYRIGHT
2017, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
5.4.2 Jun 24, 2017 mgd77convert(1)
gmt5 5.4.2 - Generated Thu Jun 29 14:06:23 CDT 2017