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<title>MGD77MANAGE</title>
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<body bgcolor="#ffffff">
<h1 align=center>MGD77MANAGE</h1>
<a href="#NAME">NAME</a><br>
<a href="#SYNOPSIS">SYNOPSIS</a><br>
<a href="#DESCRIPTION">DESCRIPTION</a><br>
<a href="#OPTIONS">OPTIONS</a><br>
<a href="#EXAMPLES">EXAMPLES</a><br>
<a href="#DISCUSSION">DISCUSSION</a><br>
<a href="#CREDITS">CREDITS</a><br>
<a href="#SEE ALSO">SEE ALSO</a><br>
<a href="#REFERENCES">REFERENCES</a><br>
<hr>
<a name="NAME"></a>
<h2>NAME</h2>
<p style="margin-left:11%; margin-top: 1em">mgd77manage
− Manage extra columns in MGD77+ files</p>
<a name="SYNOPSIS"></a>
<h2>SYNOPSIS</h2>
<p style="margin-left:11%; margin-top: 1em"><b>mgd77manage</b>
<i>NGDC-ids</i> [
<b>−A</b>[<b>+</b>]<b>a</b>|<b>c</b>|<b>d</b>|<b>D</b>|<b>e</b>|<b>E</b>|<b>g</b>|<b>i</b>|<b>n</b>|<b>t</b>|<b>T</b><i>fileinfo</i>
] [ <b>−Cf</b>|<b>g</b>|<b>e</b> ] [
<b>−D</b><i>abbrev1,abbrev2,...</i> ] [
<b>−E</b><i>empty</i> ] [ <b>−F</b> ] [
<b>−I</b><i>abbrev</i>/<i>name</i>/<i>unit</i>/<b>t</b>/<i>scale</i>/<i>offset</i>/<i>comment</i>
] [ <b>−Ne</b>|<b>k</b>|<b>m</b>|<b>n</b> ] [
<b>−Q</b>[<b>b</b>|<b>c</b>|<b>l</b>|<b>n</b>][[<b>/</b>]<i>threshold</i>]
] [ <b>−V</b> ] [
<b>−bi</b>[<b>s</b>|<b>S</b>|<b>d</b>|<b>D</b>[<i>ncol</i>]|<b>c</b>[<i>var1</i><b>/</b><i>...</i>]]
]</p>
<a name="DESCRIPTION"></a>
<h2>DESCRIPTION</h2>
<p style="margin-left:11%; margin-top: 1em"><b>mgd77manage</b>
deals with maintaining extra custom columns in MGD77+ netCDF
files. You can either delete one or more columns, add a new
column, update an existing column with new data, or supply
error correction information (*.e77 files). New data may
come from a table (ASCII unless <b>−b</b> is used), be
based on existing columns and certain theoretical
expressions, or they may be obtained by sampling a grid
(choose between GMT grid or a Sandwell/Smith Mercator *.img
grid) along track. The new data will be appended to the
MGD77+ file in the form of an extra data column of specified
type. The data file will be modified; no new file will be
created. For the big issues, see the DISCUSSION section
below. <i><br>
NGDC-ids</i></p>
<p style="margin-left:22%;">Can be one or more of five
kinds of specifiers: <br>
1) 8-character NGDC IDs, e.g., 01010083, JA010010etc., etc.
<br>
2) 2-character <agency> codes which will return all
cruises from each agency. <br>
3) 4-character <agency><vessel> codes, which
will return all cruises from those vessels. <br>
4) =<list>, where <list> is a table with NGDC
IDs, one per line. <br>
5) If nothing is specified we return all cruises in the data
base. <br>
(See mgd77info <b>−L</b> for agency and vessel codes).
The ".mgd77" or ".nc" extensions will
automatically be appended, if needed (use <b>−I</b> to
ignore certain file types). Cruise files will be looked for
first in the current directory and second in all directories
listed in <b>$MGD77_HOME</b>/mgd77_paths.txt [If
<b>$MGD77_HOME</b> is not set it will default to
<b>$GMT_SHAREDIR</b>/mgd77].</p>
<a name="OPTIONS"></a>
<h2>OPTIONS</h2>
<p style="margin-left:11%; margin-top: 1em">No space
between the option flag and the associated arguments</p>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−A</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Add a new data
column. If an existing column with the same abbreviation
already exists in the file we will cowardly refuse to update
the file. Specifying <b>−A+</b> overcomes this
reluctance (However, sometimes an existing column cannot be
upgraded without first deleting it; if so you will be
warned). Select a column source code among <b>a</b>,
<b>c</b>, <b>d</b>, <b>D</b>, <b>e</b>, <b>g</b>, <b>i</b>,
<b>n</b>, <b>t</b>, or <b>T</b>; detailed descriptions for
each choice follow:</p></td>
</table>
<p style="margin-left:22%; margin-top: 1em"><b>a</b> Append
filename of a single column table to add. File must have the
same number of rows as the MGD77+ file. If no file is given
we read from stdin instead.</p>
<p style="margin-left:22%; margin-top: 1em"><b>c</b> Create
a new column that derives from existing data or formulas for
corrections and reference fields. Append <b>c</b> for the
Carter corrections subtracted from uncorrected depths,
<b>g</b> for the IGF gravity reference field (a.k.a
"normal gravity"), <b>m</b> for the IGRF total
field magnetic reference field, and <b>r</b> for recomputed
magnetic anomaly (append 1 or 2 to specify which total field
column to use [1]). For gravity we choose the reference
field based on the parameter Gravity Theoretical Formula
Code in the cruise’s MGD77 header. If this is not set
or is invalid we default to the IGF 1980. You can override
this behaviour by appending the desired code: 1 = Heiskanen
1924, 2 = International 1930, 3 = IGF1967, or 4 =
IGF1980.</p>
<p style="margin-left:22%; margin-top: 1em"><b>d</b> Append
filename of a two-column table with the first column holding
distances along track and the second column holding data
values. If no file is given we read from stdin instead.
Records with matching distances in the MGD77+ file will be
assigned the new values; at other distances we set them to
NaN. Alternatively, give upper case <b>D</b> instead and we
will interpolate the column at all record distances. See
<b>−N</b> for choosing distance units and
<b>−C</b> for choosing how distances are
calculated.</p>
<p style="margin-left:22%; margin-top: 1em"><b>e</b>
Expects to find an e77 error/correction log from
<b><A HREF="mgd77sniffer.html">mgd77sniffer</A></b> with the name <i>NGDC_ID</i>.e77 in the
current directory or in $MGD77_HOME/E77; this file will
examined and used to make modifications to the header
values, specify a systematic correction for certain columns
(such as scale and offset), specify that a certain anomaly
should be recalculated from the observations (e.g.,
recalculate mag from mtf1 and the latest IGRF), and add or
update the special column <b>flag</b> which may hold
bitflags (0 = GOOD, 1 = BAD) for each data field in the
standard MGD77 data set. Any fixed correction terms found
(such as needing to scale a field by 0.1 or 10 because the
source agency used incorrect units) will be written as
attributes to the netCDF MGD77+ file and applied when the
data are read by <b><A HREF="mgd77list.html">mgd77list</A></b>. Ephemeral corrections
such as those determined by crossover analysis are not kept
in the data files but reside in correction tables (see
<b><A HREF="mgd77list.html">mgd77list</A></b> for details). By default, the first
character of each header line in the e77 file (which is ?, Y
or N) will be consulted to see if the corresponding
adjustment should be applied. If any undecided settings are
found (i.i, ?) we will abort and make no changes. Only
records marked Y will be porcessed. You can override this
behavior by appending one or more modifiers to the
<b>−Ae</b> command: <b>h</b> will ignore all header
corrections, <b>f</b> will ignore all fixed systematic trend
corrections, <b>n</b>, <b>v</b>, and <b>s</b> will ignore
bitflags pertaining to navigation, data values, and data
slopes, respectively. Use <b>−A+e</b> to replace any
existing E77 corrections in the file with the new values.
Finally, e77 corrections will not be applied if the E77 file
has not been verified. Use <b>−AE</b> to ignore the
verification status.</p>
<p style="margin-left:22%; margin-top: 1em"><b>g</b> Sample
a GMT geographic (lon, lat) grid along the track given by
the MGD77+ file using bicubic interpolation (however, see
<b>−Q</b>). Append name of a GMT grid file.</p>
<p style="margin-left:22%; margin-top: 1em"><b>i</b> Sample
a Sandwell/Smith Mercator *.img grid along the track given
by the MGD77+ file using bicubic interpolation (however, see
<b>−Q</b>). Append the img grid filename, followed by
the comma-separated data scale (typically 1 or 0.1), the IMG
file mode (0-3), and optionally the img grid max latitude
[80.738]. The modes stand for the following: (0) Img files
with no constraint code, returns data at all points, (1) Img
file with constraints coded, return data at all points, (2)
Img file with constraints coded, return data only at
constrained points and NaN elsewhere, and (3) Img file with
constraints coded, return 1 at constraints and 0
elsewhere.</p>
<p style="margin-left:22%; margin-top: 1em"><b>n</b> Append
filename of a two-column table with the first column holding
the record number (0 to nrows - 1) and the second column
holding data values. If no file is given we read from stdin
instead. Records with matching record numbers in the MGD77+
file will be assigned the new values; at other records we
set them to NaN.</p>
<p style="margin-left:22%; margin-top: 1em"><b>t</b> Append
filename of a two-column table with the first column holding
absolute times along track and the second column holding
data values. If no file is given we read from stdin instead.
Records with matching times in the MGD77+ file will be
assigned the new values; at other times we set them to NaN.
Alternatively, give upper case <b>T</b> instead and we will
interpolate the column at all record times.</p>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−C</b></p> </td>
<td width="4%"></td>
<td width="82%">
<p style="margin-top: 1em" valign="top">Append a one-letter
code to select the procedure for along-track distance
calculation when using <b>−Ad</b>|<b>D</b> (see
<b>−N</b> for selecting distance units):</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%"></td>
<td width="4%"></td>
<td width="82%">
<p valign="top"><b>f</b> Flat Earth distances.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%"></td>
<td width="4%"></td>
<td width="82%">
<p valign="top"><b>g</b> Great circle distances
[Default].</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%"></td>
<td width="4%"></td>
<td width="82%">
<p valign="top"><b>e</b> Geodesic distances on current GMT
ellipsoid.</p> </td>
</table>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−D</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Give a
comma-separated list of column abbreviations that you want
to delete from the MGD77+ files. Do NOT use this option to
remove columns that you are replacing with new data (use
<b>−A+</b> instead). Because we cannot remove
variables from netCDF files we must create a new file
without the columns to be deleted. Once the file is
successfully created we temporarily rename the old file,
change the new filename to the old filename, and finally
remove the old, renamed file.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−E</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Give a single
character that will be repeated to fill empty string values,
e.g., ’9’ will yield a string like
"99999..." [9].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−F</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Force mode. When
this mode is active you are empowered to delete or replace
even the standard MGD77 set of columns. You better know what
you are doing!</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−I</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">In addition to file
information we must specify additional information about the
extra column. Specify a short (16 char or less, using lower
case letters, digits, or underscores only) abbreviation for
the selected data, its more descriptive name, the data unit,
the data type 1-character code (<b>b</b>yte, <b>s</b>hort,
<b>f</b>loat, <b>i</b>nt, <b>d</b>ouble, or <b>t</b>ext) you
want used for storage in the netCDF file, any scale and
offset we should apply to the data to make them fit inside
the range implied by the chosen storage type, and a general
comment (< 128 characters) regarding what these data
represent. Note: If text data type is selected then the
terms "values" in the <b>−A</b> discussion
refer to your text data. Furthermore, the discussion on
interpolation does not apply and the NaN value becomes a
"no string" value (see <b>−E</b> for what
this is). Place quotes around terms with more than one word
(e.g., "Corrected Depth").</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−N</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Specify the
distance unit used when using <b>−Ad</b>|<b>D</b> by
appending <b>e</b> (meter), <b>k</b> (km), <b>m</b> (miles),
or <b>n</b> (nautical miles). [Default is <b>−Nk</b>
(km)].</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−Q</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Quick mode, use
bilinear rather than bicubic interpolation [Default].
Alternatively, select the interpolation mode by adding
<b>b</b> for B-spline smoothing, <b>c</b> for bicubic
interpolation, <b>l</b> for bilinear interpolation or
<b>n</b> for nearest-neighbor value. Optionally, append
<i>threshold</i> in the range [0,1]. This parameter controls
how close to nodes with NaN values the interpolation will
go. E.g., a <i>threshold</i> of 0.5 will interpolate about
half way from a non-NaN to a NaN node, whereas 0.1 will go
about 90% of the way, etc. [Default is 1, which means none
of the (4 or 16) nearby nodes may be NaN]. <b>−Q0</b>
will just return the value of the nearest node instead of
interpolating. This is the same as using <b>−Qn</b>.
Only relevant when <b>−Ag</b>|<b>i</b> is
selected.</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−V</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Selects verbose
mode, which will send progress reports to stderr [Default
runs "silently"].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="4%">
<p style="margin-top: 1em" valign="top"><b>−bi</b></p> </td>
<td width="7%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Selects binary
input. Append <b>s</b> for single precision [Default is
<b>d</b> (double)]. Uppercase <b>S</b> or <b>D</b> will
force byte-swapping. Optionally, append <i>ncol</i>, the
number of columns in your binary input file if it exceeds
the columns needed by the program. Or append <b>c</b> if the
input file is netCDF. Optionally, append
<i>var1</i><b>/</b><i>var2</i><b>/</b><i>...</i> to specify
the variables to be read. This applies to the input 1- or
2-column data files specified under some of the
<b>−A</b> options. The binary input option is only
available for numerical data columns.</p></td>
</table>
<a name="EXAMPLES"></a>
<h2>EXAMPLES</h2>
<p style="margin-left:11%; margin-top: 1em">To append
Geosat/ERS-1 gravity version 11.2 as an extra data column in
the cruises 01010047.nc and 01010008.nc, storing the values
as mGal*10 in a 2-byte short integer, try</p>
<p style="margin-left:11%; margin-top: 1em"><b>mgd77manage</b>
01010047 01010008 <b>−Ai</b>10/1/grav.11.2.img
<b>−I</b>satgrav/"Geosat/ERS-1
gravity"/"mGal"/s/10/0/"Sandwell/Smith
version 11.2" <b>−V</b></p>
<p style="margin-left:11%; margin-top: 1em">To append a
filtered version of magnetics as an extra data column of
type float for the cruise 01010047.nc, and interpolate the
filtered data at the times given in the MGD77+ file, try</p>
<p style="margin-left:11%; margin-top: 1em"><b>mgd77manage</b>
01010047 <b>−AT</b>mymag.tm
<b>−I</b>filtmag/"Intermediate-wavelength
magnetic
residuals"/"nTesla"/f/1/0/"Useful for
looking for isochrons" <b>−V</b></p>
<p style="margin-left:11%; margin-top: 1em">To delete the
existing extra columns satfaa, coastdist, and satvgg from
all MGD77+ files, try</p>
<p style="margin-left:11%; margin-top: 1em"><b>mgd77manage</b>
‘cat allmgd77.lis‘
<b>−D</b>satfaa,coastdist,satvgg <b>−V</b></p>
<p style="margin-left:11%; margin-top: 1em">To create a
4-byte float column with the correct IGRF reference field in
all MGD77+ files, try</p>
<p style="margin-left:11%; margin-top: 1em"><b>mgd77manage</b>
‘cat allmgd77.lis‘ <b>−Acm
−I</b>igrf/"IGRF reference
field"/"nTesla"/f/1/0/"IGRF version 10
for 1990-2010" <b>−V</b></p>
<a name="DISCUSSION"></a>
<h2>DISCUSSION</h2>
<p style="margin-left:11%; margin-top: 1em"><b>1.
Preamble</b> <br>
The mgd77 supplement is an attempt to (1) improve on the
limited functionality of the existing mgg supplement, (2)
incorporate some of the ideas from Scripps’ gmt+
supplement by allowing extra data columns, and (3) add new
capabilities for managing marine geophysical trackline data
stored in an architecture-independent CF-1.0- and
COARDS-compliant netCDF file format. Here are some of the
underlying ideas and steps you need to take to maintain your
files.</p>
<p style="margin-left:11%; margin-top: 1em"><b>2.
Introduction</b> <br>
Our starting point is the MGD77 ASCII data files distributed
from NGDC on CD-ROMS, DVD-ROMS, and via FTP. Using Geodas to
install the files locally we choose the "Carter
corrected depth" option which will fill in the depth
column using the two-way traveltimes and the Carter tables
if twt is present. This step yields ~5000 individual cruise
files. Place these in one or more sub-directories of your
choice, list these sub-directories (one per line) in the
file mgd77_paths.txt, and place that file in the directory
pointed to by <b>$MGD77_HOME</b>; if not set this variable
defaults to <b>$GMT_SHAREDIR</b>/mgd77.</p>
<p style="margin-left:11%; margin-top: 1em"><b>3.
Conversion</b> <br>
Convert the ASCII MGD77 files to the new netCDF MGD77+
format using <b><A HREF="mgd77convert.html">mgd77convert</A></b>. Typically, you will make a
list of all the cruises to be converted (with or without
extension), and you then run</p>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="8%"></td>
<td width="92%">
<p valign="top"><b>mgd77convert −Fa −Tc
−V −Lwe+</b> ‘cat cruises.lis‘ >
log.txt</p> </td>
</table>
<p style="margin-left:11%; margin-top: 1em">The verbose
settings will ensure that all problems found during
conversion will be reported. The new *.nc files may also be
placed in one or more separate sub-directories and these
should also be listed in the mgd77_paths.txt file. We
suggest you place the directories with *.nc files ahead of
the *.mgd77 directories. When you later want to limit a
search to files of a certain extension you should use the
<b>−I</b> option.</p>
<p style="margin-left:11%; margin-top: 1em"><b>4. Adding
new columns <br>
mgd77manage</b> will allow you to add additional data
columns to your *.nc files. These can be anything, including
text strings, but most likely are numerical values sampled
along the track from a supplied grid or an existing column
that have been filtered or manipulated for a particular
purpose. The format supports up to 32 such extra columns.
See this man page for how to add columns. You may later
decide to remove some of these columns or update the data
associated with a certain column. Data extraction tools such
as <b><A HREF="mgd77list.html">mgd77list</A></b> can be used to extract a mix of standard
MGD77 columns (navigation, time, and the usual geophysical
observations) and your custom columns.</p>
<p style="margin-left:11%; margin-top: 1em"><b>5. Error
sources</b> <br>
Before we discuss how to correct errors we will first list
the different classes of errors associated with MGD77 data:
(1) Header record errors occur when some of the information
fields in the header do not comply with the MGD77
specification or required information is missing.
<b><A HREF="mgd77convert.html">mgd77convert</A></b> will list these errors when the extended
verbose setting is selected. These errors typically do not
affect the data and are instead errors in the
<i>meta-data</i> (2) Fixed systematic errors occur when a
particular data column, despite the MGD77 specification, has
been encoded incorrectly. This usually means the data will
be off by a constant factor such as 10 or 0.1, or in some
cases even 1.8288 which converts fathoms to meters. (3)
Unknown systematic errors occur when the instrument that
recorded the data or the processing that followed introduced
signals that appear to be systematic functions of time along
track, latitude, heading, or some other combination of terms
that have a physical or logical explanation. These terms may
sometimes be resolved by data analysis techniques such as
along-track and across-track investigations, and will result
in correction terms that when applied to the data will
remove these unwanted signals in an optimal way. Because
these correction terms may change when new data are
considered in their determination, such corrections are
considered to be ephemeral. (4) Individual data points or
sequences of data may violate rules such as being outside of
possible ranges or in other ways violate sanity.
Furthermore, sequences of points that may be within valid
ranges may give rise to data gradients that are
unreasonable. The status of every point can therefore be
determined and this gives rise to bitflags GOOD or BAD. Our
policy is that error sources 1, 2, and 4 will be corrected
by supplying the information as meta-data in the relevant
*.nc files, whereas the corrections for error source 3
(because they will constantly be improved) will be
maintained in a separate list of corrections.</p>
<p style="margin-left:11%; margin-top: 1em"><b>6. Finding
errors</b> <br>
The <b><A HREF="mgd77sniffer.html">mgd77sniffer</A></b> is a tool that does a thorough
along-track sanity check of the original MGD77 ASCII files
and produces a corresponding *.e77 error log. All problems
found are encoded in the error log, and recommended fixed
correction terms are given, if needed. An analyst may verify
that the suggested corrections are indeed valid (we only
want to correct truly obvious unit errors), edit these error
logs and modify such correction terms and activate them by
changing the relevant code key (see <b><A HREF="mgd77sniffer.html">mgd77sniffer</A></b> for
more details). <b>mgd77manage</b> can ingest these error
logs and (1) correct bad header records given the
suggestions in the log, (2) insert scale/offset correction
terms to be used when reading certain columns, and (3)
insert any bit-flags found. Rerun this step if you later
find other problems as all E77 settings or flags will be
recreated based on the latest E77 log.</p>
<p style="margin-left:11%; margin-top: 1em"><b>7. Error
corrections</b> <br>
The extraction program <b><A HREF="mgd77list.html">mgd77list</A></b> allows for
corrections to be applied on-the-fly when data are
requested. First, data with BAD bitflags are suppressed.
Second, data with fixed systematic correction terms are
corrected accordingly. Third, data with ephemeral correction
terms will have those corrections applied (if a correction
table is supplied). All of these steps require the presence
of the relevant meta-data and all can be overruled by the
user. In addition, users may add their own bitflags as
separate data columns and use <b><A HREF="mgd77list.html">mgd77list</A></b>’s
logical tests to further dictate which data are suppressed
from output.</p>
<a name="CREDITS"></a>
<h2>CREDITS</h2>
<p style="margin-left:11%; margin-top: 1em">The IGRF
calculations are based on a Fortran program written by Susan
Macmillan, British Geological Survey, translated to C via
f2c by Joaquim Luis, and adapted to GMT style by Paul
Wessel.</p>
<a name="SEE ALSO"></a>
<h2>SEE ALSO</h2>
<p style="margin-left:11%; margin-top: 1em"><i><A HREF="mgd77convert.html">mgd77convert</A></i>(1),
<i><A HREF="mgd77list.html">mgd77list</A></i>(1), <i><A HREF="mgd77info.html">mgd77info</A></i>(1),
<i><A HREF="mgd77sniffer.html">mgd77sniffer</A></i>(1) <i><A HREF="mgd77track.html">mgd77track</A></i>(1)
<i><A HREF="x2sys_init.html">x2sys_init</A></i>(1)</p>
<a name="REFERENCES"></a>
<h2>REFERENCES</h2>
<p style="margin-left:11%; margin-top: 1em">Wessel, P., and
W. H. F. Smith, 2009, The Generic Mapping Tools (GMT)
version 4.5.0 Technical Reference & Cookbook,
SOEST/NOAA. <br>
Wessel, P., and W. H. F. Smith, 1998, New, Improved Version
of Generic Mapping Tools Released, EOS Trans., AGU, 79 (47),
p. 579. <br>
Wessel, P., and W. H. F. Smith, 1995, New Version of the
Generic Mapping Tools Released, EOS Trans., AGU, 76 (33), p.
329. <br>
Wessel, P., and W. H. F. Smith, 1995, New Version of the
Generic Mapping Tools Released,
http://www.agu.org/eos_elec/95154e.html, Copyright 1995 by
the American Geophysical Union. <br>
Wessel, P., and W. H. F. Smith, 1991, Free Software Helps
Map and Display Data, EOS Trans., AGU, 72 (41), p. 441. <br>
The Marine Geophysical Data Exchange Format -
"MGD77", see
<i>http://www.ngdc.noaa.gov/mgg/dat/geodas/docs/mgd77.txt</i>
<br>
IGRF, see
<i>http://www.ngdc.noaa.gov/IAGA/vmod/igrf.html</i></p>
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