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mgd77convert - Convert MGD77 data to other file formats


mgd77convert NGDC-ids a|c|m |t [+]a|c|m|t [ ] [ ] [ [w][e][+] ] [ [level] ]

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


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.


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

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].

-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 MGD77 t 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 MGD77 t 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


-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].

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
use just -).

-+ 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 options, then

Print GMT version and exit.

Print full path to GMT share directory and exit.


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,

gmt mgd77convert 01020051 -FC -Ta -V


mgd77convert handles three different formats. (1) The MGD77 ASCII tables are the
established standard for distribution of underway geophysical data to and from the NGDC
data center. 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. (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
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.


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

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