mgd77track - Plot track-line map of MGD77 cruises


mgd77track NGDC-ids -Rregion -Jparameters [ -A[c][size][,spacing] ] [ -B[p|s]parameters ] [ -Cf|g|e ] [ -Dastartdate ] [ -Dbstopdate ] [ -F ] [ -Gd|t|ngap ] [ -Iignore ] [ -K ] [ -Ltrackticks ] [ -oflags ] [ -pflags ] [ -Sastartdist[u] ] [ -Sbstopdist[u] ] [ -TT|t|dms,mc,mfs,mf,mfc ] [ -U[stamp] ] [ -V[level] ] [ -W[-|+][pen] ] [ -Xx_offset ] [ -Yy_offset ] [ -pflags ] [ -ttransp ]

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


mgd77track reads NGDC MGD77 cruises and creates PostScript code that will plot one or more ship tracks on a map using the specified projection. The PostScript code is written to standard output.

Required Arguments


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].

-Jparameters (more …)
Select map projection.
west, east, south, and north specify the region of interest, and you may specify them in decimal degrees or in [±]dd:mm[][W|E|S|N] format Append +r if lower left and upper right map coordinates are given instead of w/e/s/n. The two shorthands -Rg and -Rd stand for global domain (0/360 and -180/+180 in longitude respectively, with -90/+90 in latitude). Alternatively for grid creation, give Rcodelon/lat/nx/ny, where code is a 2-character combination of L, C, R (for left, center, or right) and T, M, B for top, middle, or bottom. e.g., BL for lower left. This indicates which point on a rectangular region the lon/lat coordinate refers to, and the grid dimensions nx and ny with grid spacings via -I is used to create the corresponding region. Alternatively, specify the name of an existing grid file and the -R settings (and grid spacing, if applicable) are copied from the grid. Appending +uunit expects projected (Cartesian) coordinates compatible with chosen -J and we inversely project to determine actual rectangular geographic region. For perspective view (-p), optionally append /zmin/zmax. In case of perspective view (-p), a z-range (zmin, zmax) can be appended to indicate the third dimension. This needs to be done only when using the -Jz option, not when using only the -p option. In the latter case a perspective view of the plane is plotted, with no third dimension.

Optional Arguments

Append c to annotate using the MGD77 cruise ID [Default uses the filename prefix]. Optional size is the font size in points. The leg annotation font is controlled by FONT_LABEL. By default, each leg is annotated every time it enters the map region. Alternatively, append ,spacing to place this label every spacing units apart along the track. Append one of the units k (km), n (nautical mile), d (day), or h (hour).
-B[p|s]parameters (more …)
Set map boundary frame and axes attributes.
Select procedure for along-track distance calculation:
f Flat Earth distances. g Great circle distances [Default]. e Geodesic distances on current GMT ellipsoid.
Do not plot data collected before startdate (yyyy-mm-ddT[hh:mm:ss]) [Default is first day].
Do not plot data collected after stopdate (yyyy-mm-ddT[hh:mm:ss]). [Default is last day].
Do not apply the error bit flags if present in a MGD77+ file [Default will apply these flags upon reading the data].
Let successive point separations exceeding dgap (km) or tgap (minutes) indicate a break in the track where we should not draw a line [no gaps recognized]. Repeat to use both types of gap checking. The nN form is used to plot only one every other N points. This is useful to reduce plot file size bat cannot be used (will be ignored) with the other two gap types.
Ignore certain data file formats from consideration. Append a|c|m|t to ignore MGD77 ASCII, MGD77+ netCDF, MGD77T ASCII, or plain table files, respectively. The option may be repeated to ignore more than one format. [Default ignores none].
-K (more …)
Do not finalize the PostScript plot.
To put time/distance log-marks on the track. E.g. a500ka24ht6h means (a)nnotate every 500 km (k) and 24 h(ours), with (t)ickmarks every 500 km and 6 hours. Alternatively you may use the modifiers d (days) and n (nautical miles).
-O (more …)
Append to existing PostScript plot.
-P (more …)
Select “Portrait” plot orientation.
Do not plot data that are less than startdist meter along track from port of departure. Append k for km, m for miles, or n for nautical miles [Default is 0 meters].
Do not plot data that are more than stopdist meter along track from port of departure. Append k for km, m for miles, or n for nautical miles [Default is end of track].
Controls the attributes of the three kinds of markers (T for the first time marker in a new day, t for additional time markers in the same day, and d for distance markers). For each of these you can specify the 5 comma-separated attributes markersize, markercolor, markerfontsize, markerfont, and markerfontcolor. Repeat the -T option for each marker type.
-U[[just]/dx/dy/][c|label] (more …)
Draw GMT time stamp logo on plot.
Append pen used for the trackline. [Defaults: width = default, color = black, style = solid]. A leading + will use the lookup color (via -C) for both symbol fill and outline pen color, while a leading - will set outline pen color and turn off symbol fill.


-Y[a|c|f|r][y-shift[u]] (more …)
Shift plot origin.
-V[level] (more …)
Select verbosity level [c].
-p[x|y|z]azim[/elev[/zlevel]][+wlon0/lat0[/z0]][+vx0/y0] (more …)
Select perspective view.
-t[transp] (more …)
Set PDF transparency level in percent.
-^ 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.


To generate a Mercator plot of the track of the cruise 01010007 in the area 70W to 20E, 40S to 20N, using a Mercator scale of 0.1inch/degree, label the tracks with 10 points characters, annotate the boundaries every 10 degrees, draw gridlines every 5 degrees, and mark the track every day and 1000 km, with ticks every 6 hours and 250 km, and send the plot to the default printer, enter the following command:

gmt mgd77track 01010007 -R70W/20E/40S/20N -Jm0.1 -B10g5 -A10 \
               -La1da1000kf6hf250k \| lpr


The Marine Geophysical Data Exchange Format - MGD77, see