Provided by: gmt-common_5.4.3+dfsg-1_all 
NAME
gmt - The Generic Mapping Tools data processing and display software package
INTRODUCTION
GMT is a collection of public-domain Unix tools that allows you to manipulate x,y and x,y,z data sets
(filtering, trend fitting, gridding, projecting, etc.) and produce PostScript illustrations ranging from
simple x-y plots, via contour maps, to artificially illuminated surfaces and 3-D perspective views in
black/white or full color. Linear, log10, and power scaling is supported in addition to over 30 common
map projections. The processing and display routines within GMT are completely general and will handle
any (x,y) or (x,y,z) data as input.
SYNOPSIS
gmt is the main program that can start any of the modules:
gmt module module-options
where module is the name of a GMT module and the options are those that pertain to that particular
module. A few special modules are also available:
gmt clear items
while delete the user’s history. Choose between history (deletes the gmt.history file in the current
directory), conf (deletes the gmt.conf file in the current directory), cache (deletes the user’s cache
directory and all of its content), or all (does all of the above).
If no module is given then several other options are available:
--help List and description of GMT modules.
--show-cores
Show number of available cores.
--show-bindir
Show directory of executables and exit.
--show-datadir
Show data directory/ies and exit.
--show-modules
List module names on stdout and exit.
--show-plugindir
Show plugin directory and exit.
--show-sharedir
Show share directory and exit.
--version
Print version and exit.
= Check if that module exist and if so the program will exit with status of 0; otherwise the status
of exit will be non-zero.
COMMAND-LINE COMPLETION
GMT provides basic command-line completion (tab completion) for bash. The completion rules are either
installed in /etc/bash_completion.d/gmt or <prefix>/share/tools/gmt_completion.bash. Depending on the
distribution, you may still need to source the gmt completion file from ~/.bash_completion or ~/.bashrc.
For more information see Section command-line-completion in the CookBook.
GMT OVERVIEW
The following is a summary of all the programs supplied with GMT and a very short description of their
purpose. Detailed information about each program can be found in the separate manual pages.
┌───────────────┬───────────────────────┐
│blockmean │ │
├───────────────┼───────────────────────┤
│blockmedian │ │
├───────────────┼───────────────────────┤
│blockmode │ │
├───────────────┼───────────────────────┤
│filter1d │ │
├───────────────┼───────────────────────┤
│fitcircle │ │
├───────────────┼───────────────────────┤
│gmt2kml │ │
├───────────────┼───────────────────────┤
│gmtconnect │ │
├───────────────┼───────────────────────┤
│gmtconvert │ │
├───────────────┼───────────────────────┤
│gmtdefaults │ │
├───────────────┼───────────────────────┤
│gmtget │ │
├───────────────┼───────────────────────┤
│gmtinfo │ │
├───────────────┼───────────────────────┤
│gmtmath │ │
├───────────────┼───────────────────────┤
│gmtselect │ │
├───────────────┼───────────────────────┤
│gmtset │ │
├───────────────┼───────────────────────┤
│gmtspatial │ │
├───────────────┼───────────────────────┤
│gmtsimplify │ │
├───────────────┼───────────────────────┤
│gmtvector │ │
├───────────────┼───────────────────────┤
│gmtwhich │ │
├───────────────┼───────────────────────┤
│grd2cpt │ │
├───────────────┼───────────────────────┤
│grd2rgb │ │
├───────────────┼───────────────────────┤
│grd2xyz │ │
├───────────────┼───────────────────────┤
│grdblend │ │
├───────────────┼───────────────────────┤
│grdclip │ │
├───────────────┼───────────────────────┤
│grdcontour │ │
├───────────────┼───────────────────────┤
│grdconvert │ │
├───────────────┼───────────────────────┤
│grdcut │ │
├───────────────┼───────────────────────┤
│grdedit │ │
├───────────────┼───────────────────────┤
│grdfft │ │
├───────────────┼───────────────────────┤
│grdfilter │ │
├───────────────┼───────────────────────┤
│grdgradient │ │
├───────────────┼───────────────────────┤
│grdhisteq │ │
└───────────────┴───────────────────────┘
│grdimage │ │
├───────────────┼───────────────────────┤
│grdinfo │ │
├───────────────┼───────────────────────┤
│grdlandmask │ │
├───────────────┼───────────────────────┤
│grdmask │ │
├───────────────┼───────────────────────┤
│grdmath │ │
├───────────────┼───────────────────────┤
│grdpaste │ │
├───────────────┼───────────────────────┤
│grdproject │ │
├───────────────┼───────────────────────┤
│grdraster │ │
├───────────────┼───────────────────────┤
│grdsample │ │
├───────────────┼───────────────────────┤
│grdtrack │ │
├───────────────┼───────────────────────┤
│grdtrend │ │
├───────────────┼───────────────────────┤
│grdvector │ │
├───────────────┼───────────────────────┤
│grdview │ │
├───────────────┼───────────────────────┤
│grdvolume │ │
├───────────────┼───────────────────────┤
│greenspline │ │
├───────────────┼───────────────────────┤
│kml2gmt │ │
├───────────────┼───────────────────────┤
│makecpt │ │
├───────────────┼───────────────────────┤
│mapproject │ │
├───────────────┼───────────────────────┤
│nearneighbor │ │
├───────────────┼───────────────────────┤
│project │ │
├───────────────┼───────────────────────┤
│psbasemap │ │
├───────────────┼───────────────────────┤
│psclip │ │
├───────────────┼───────────────────────┤
│pscoast │ │
├───────────────┼───────────────────────┤
│pscontour │ │
├───────────────┼───────────────────────┤
│psconvert │ │
├───────────────┼───────────────────────┤
│pshistogram │ │
├───────────────┼───────────────────────┤
│psimage │ │
├───────────────┼───────────────────────┤
│pslegend │ │
├───────────────┼───────────────────────┤
│psmask │ │
├───────────────┼───────────────────────┤
│psrose │ │
├───────────────┼───────────────────────┤
│psscale │ │
├───────────────┼───────────────────────┤
│pstext │ │
└───────────────┴───────────────────────┘
│pswiggle │ │
├───────────────┼───────────────────────┤
│psxy │ │
├───────────────┼───────────────────────┤
│psxyz │ │
├───────────────┼───────────────────────┤
│sample1d │ │
├───────────────┼───────────────────────┤
│spectrum1d │ │
├───────────────┼───────────────────────┤
│splitxyz │ │
├───────────────┼───────────────────────┤
│surface │ │
├───────────────┼───────────────────────┤
│trend1d │ │
├───────────────┼───────────────────────┤
│trend2d │ │
├───────────────┼───────────────────────┤
│triangulate │ │
├───────────────┼───────────────────────┤
│xyz2grd │ │
├───────────────┼───────────────────────┤
│ │ Supplement gshhg: │
├───────────────┼───────────────────────┤
│gshhg │ │
├───────────────┼───────────────────────┤
│ │ Supplement img: │
├───────────────┼───────────────────────┤
│img2grd │ │
├───────────────┼───────────────────────┤
│ │ Supplement meca: │
├───────────────┼───────────────────────┤
│pscoupe │ │
├───────────────┼───────────────────────┤
│psmeca │ │
├───────────────┼───────────────────────┤
│pspolar │ │
├───────────────┼───────────────────────┤
│psvelo │ │
├───────────────┼───────────────────────┤
│pssac │ │
├───────────────┼───────────────────────┤
│ │ Supplement mgd77: │
├───────────────┼───────────────────────┤
│mgd77convert │ │
├───────────────┼───────────────────────┤
│mgd77header │ │
├───────────────┼───────────────────────┤
│mgd77info │ │
├───────────────┼───────────────────────┤
│mgd77list │ │
├───────────────┼───────────────────────┤
│mgd77magref │ │
├───────────────┼───────────────────────┤
│mgd77manage │ │
├───────────────┼───────────────────────┤
│mgd77path │ │
├───────────────┼───────────────────────┤
│mgd77sniffer │ │
├───────────────┼───────────────────────┤
│mgd77track │ │
├───────────────┼───────────────────────┤
│ │ Supplement potential: │
└───────────────┴───────────────────────┘
│gmtgravmag3d │ │
├───────────────┼───────────────────────┤
│gmtflexure │ │
├───────────────┼───────────────────────┤
│gpsgridder │ │
├───────────────┼───────────────────────┤
│gravfft │ │
├───────────────┼───────────────────────┤
│grdflexure │ │
├───────────────┼───────────────────────┤
│grdgravmag3d │ │
├───────────────┼───────────────────────┤
│grdredpol │ │
├───────────────┼───────────────────────┤
│grdseamount │ │
├───────────────┼───────────────────────┤
│talwani2d │ │
├───────────────┼───────────────────────┤
│talwani3d │ │
├───────────────┼───────────────────────┤
│ │ Supplement segy: │
├───────────────┼───────────────────────┤
│pssegy │ │
├───────────────┼───────────────────────┤
│pssegyz │ │
├───────────────┼───────────────────────┤
│segy2grd │ │
├───────────────┼───────────────────────┤
│ │ Supplement sph: │
├───────────────┼───────────────────────┤
│sphdistance │ │
├───────────────┼───────────────────────┤
│sphinterpolate │ │
├───────────────┼───────────────────────┤
│sphtriangulate │ │
├───────────────┼───────────────────────┤
│ │ Supplement spotter: │
├───────────────┼───────────────────────┤
│backtracker │ │
├───────────────┼───────────────────────┤
│gmtpmodeler │ │
├───────────────┼───────────────────────┤
│grdpmodeler │ │
├───────────────┼───────────────────────┤
│grdrotater │ │
├───────────────┼───────────────────────┤
│grdspotter │ │
├───────────────┼───────────────────────┤
│hotspotter │ │
├───────────────┼───────────────────────┤
│originator │ │
├───────────────┼───────────────────────┤
│rotconverter │ │
├───────────────┼───────────────────────┤
│rotsmoother │ │
├───────────────┼───────────────────────┤
│ │ Supplement x2sys: │
├───────────────┼───────────────────────┤
│x2sys_binlist │ │
├───────────────┼───────────────────────┤
│x2sys_cross │ │
├───────────────┼───────────────────────┤
│x2sys_datalist │ │
└───────────────┴───────────────────────┘
│x2sys_get │ │
├───────────────┼───────────────────────┤
│x2sys_init │ │
├───────────────┼───────────────────────┤
│x2sys_list │ │
├───────────────┼───────────────────────┤
│x2sys_merge │ │
├───────────────┼───────────────────────┤
│x2sys_put │ │
├───────────────┼───────────────────────┤
│x2sys_report │ │
├───────────────┼───────────────────────┤
│x2sys_solve │ │
└───────────────┴───────────────────────┘
CUSTOM MODULES
The gmt program can also load custom modules from shared libraries built as specified in the GMT API
documentation. This way your modules can benefit form the GMT infrastructure and extend GMT in specific
ways.
THE COMMON GMT OPTIONS
-B[p|s]parameters -Jparameters -Jz|Zparameters -K -O -P
-Rwest/east/south/north[/zmin/zmax][+r]
-U[stamp]
-V[level]
-Xx_offset
-Yy_offset -aflags -bbinary -dnodata -fflags -ggaps -hheaders -iflags -nflags -oflags -pflags -r -sflags
-ttransp -x[[-]n] -:[i|o]
DESCRIPTION
These are all the common GMT options that remain the same for all GMT programs. No space between the
option flag and the associated arguments.
-B[p|s]parameters
Set map Frame and Axes parameters. The Frame parameters are specified by
-B[axes][+b][+gfill][+n][+olon/lat][+ttitle]
where axes selects which axes to plot. By default, all 4 map boundaries (or plot axes) are plotted
(named W, E, S, N). To customize, append the codes for those you want (e.g., WSn). Upper case
means plot and annotate while lower case just plots the specified axes. If a 3-D basemap is
selected with -p and -Jz, append Z or z to control the appearance of the vertical axis. By default
a single vertical axes will be plotted at the most suitable map corner. Override the default by
appending any combination of corner ids 1234, where 1 represents the lower left corner and the
order goes counter-clockwise. Append +b to draw the outline of the 3-D cube defined by -R; this
modifier is also needed to display gridlines in the x-z, y-z planes. Note that for 3-D views the
title, if given, will be suppressed. You can paint the interior of the canvas with +gfill. Append
+n to have no frame and annotations at all [Default is controlled by the codes]. Optionally
append +oplon/plat to draw oblique gridlines about specified pole [regular gridlines]. Ignored if
gridlines are not requested (below) and disallowed for the oblique Mercator projection. To add a
plot title (+ttitle). The Frame setting is optional but can be invoked once to override the above
defaults.
The Axes parameters are specified by
-B[p|s][x|y|z]intervals[+l|Llabel][+pprefix][+uunit]
but you may also split this into two separate invocations for clarity, i.e.,
• -B[p|s][x|y|z][+l|Llabel][+pprefix][+uunit]
• -B[p|s][x|y|z]intervals
The first optional flag following -B selects p (rimary) [Default] or s (econdary) axes information
(mostly used for time axes annotations). The [x|y|z] flags specify which axes you are providing
information for. If none are given then we default to xy. If you wish to give different annotation
intervals or labels for the various axes then you must repeat the B option for each axis (If a 3-D
basemap is selected with -p and -Jz, use -Bz to give settings for the vertical axis.). To add a label
to an axis, just append +llabel (Cartesian projections only). Use +L to force a horizontal label for
y-axes (useful for very short labels). If the axis annotation should have a leading text prefix (e.g.,
dollar sign for those plots of your net worth) you can append +pprefix. For geographic maps the
addition of degree symbols, etc. is automatic (and controlled by the GMT default setting
FORMAT_GEO_MAP). However, for other plots you can add specific units by adding +uunit. If any of these
text strings contain spaces or special characters you will need to enclose them in quotes. The
intervals specification is a concatenated string made up of substrings of the form
[a|f|g]stride[+-phase][u].
The leading a is used to specify the annotation and major tick spacing [Default], f for minor tick
spacing, and g for gridline spacing. stride is the desired stride interval. The optional phase shifts
the annotation interval by that amount (positive or negative). The optional unit indicates the unit of
the stride and can be any of
• Y (year, plot with 4 digits)
• y (year, plot with 2 digits)
• O (month, plot using FORMAT_DATE_MAP)
• o (month, plot with 2 digits)
• U (ISO week, plot using FORMAT_DATE_MAP)
• u (ISO week, plot using 2 digits)
• r (Gregorian week, 7-day stride from start of week TIME_WEEK_START)
• K (ISO weekday, plot name of day)
• D (date, plot using FORMAT_DATE_MAP)
• d (day, plot day of month 0-31 or year 1-366, via FORMAT_DATE_MAP)
• R (day, same as d, aligned with TIME_WEEK_START)
• H (hour, plot using FORMAT_CLOCK_MAP)
• h (hour, plot with 2 digits)
• M (minute, plot using FORMAT_CLOCK_MAP)
• m (minute, plot with 2 digits)
• S (second, plot using FORMAT_CLOCK_MAP)
• s (second, plot with 2 digits).
Note for geographic axes m and s instead mean arc minutes and arc seconds. All entities that are
language-specific are under control by GMT_LANGUAGE. Alternatively, for linear maps, we can omit
stride, thus setting xinfo, yinfo, or zinfo to a plots annotations at automatically determined
intervals,
• ag plots both annotations and grid lines with the same spacing,
• afg adds suitable minor tick intervals,
• g plots grid lines with the same interval as if -Bf was used.
For custom annotations and intervals, let intervals be given as cintfile, where intfile contains any
number of records with coord type [label]. Here, type is one or more letters from a|i, f, and g. For
a|i you must supply a label that will be plotted at the coord location. For non-geographical
projections: Give negative scale (in -Jx) or axis length (in -JX) to change the direction of increasing
coordinates (i.e., to make the y-axis positive down). For log10 axes: Annotations can be specified in
one of three ways:
1. stride can be 1, 2, 3, or -n. Annotations will then occur at 1, 1-2-5, or 1-2-3-4-…-9, respectively;
for -n we annotate every n’t magnitude. This option can also be used for the frame and grid
intervals.
2. An l is appended to the tickinfo string. Then, log10 of the tick value is plotted at every integer
log10 value.
3. A p is appended to the tickinfo string. Then, annotations appear as 10 raised to log10 of the tick
value.
For power axes: Annotations can be specified in one of two ways:
1. stride sets the regular annotation interval.
2. A p is appended to the tickinfo string. Then, the annotation interval is expected to be in
transformed units, but the annotation value will be plotted as untransformed units. E.g., if stride
= 1 and power = 0.5 (i.e., sqrt), then equidistant annotations labeled 1-4-9… will appear.
These GMT parameters can affect the appearance of the map boundary: MAP_ANNOT_MIN_ANGLE,
MAP_ANNOT_MIN_SPACING, FONT_ANNOT_PRIMARY, FONT_ANNOT_SECONDARY, MAP_ANNOT_OFFSET_PRIMARY,
MAP_ANNOT_OFFSET_SECONDARY, MAP_ANNOT_ORTHO, MAP_FRAME_AXES, MAP_DEFAULT_PEN, MAP_FRAME_TYPE,
FORMAT_GEO_MAP, MAP_FRAME_PEN, MAP_FRAME_WIDTH, MAP_GRID_CROSS_SIZE_PRIMARY, MAP_GRID_PEN_PRIMARY,
MAP_GRID_CROSS_SIZE_SECONDARY, MAP_GRID_PEN_SECONDARY, FONT_TITLE, FONT_LABEL, MAP_LINE_STEP,
MAP_ANNOT_OBLIQUE, FORMAT_CLOCK_MAP, FORMAT_DATE_MAP, FORMAT_TIME_PRIMARY_MAP,
FORMAT_TIME_SECONDARY_MAP, GMT_LANGUAGE, TIME_WEEK_START, MAP_TICK_LENGTH_PRIMARY, and
MAP_TICK_PEN_PRIMARY; see the gmt.conf man page for details.
-Jparameters
Select map projection. The following character determines the projection. If the character is upper case
then the argument(s) supplied as scale(s) is interpreted to be the map width (or axis lengths), else the
scale argument(s) is the map scale (see its definition for each projection). UNIT is cm, inch, or point,
depending on the PROJ_LENGTH_UNIT setting in gmt.conf, but this can be overridden on the command line by
appending c, i, or p to the scale or width values. Append h, +, or - to the given width if you instead
want to set map height, the maximum dimension, or the minimum dimension, respectively [Default is w for
width]. In case the central meridian is an optional parameter and it is being omitted, then the center
of the longitude range given by the -R option is used. The default standard parallel is the equator. The
ellipsoid used in the map projections is user-definable by editing the gmt.conf file in your home
directory. 73 commonly used ellipsoids and spheroids are currently supported, and users may also specify
their own custom ellipsoid parameters [Default is WGS-84]. Several GMT parameters can affect the
projection: PROJ_ELLIPSOID, GMT_INTERPOLANT, PROJ_SCALE_FACTOR, and PROJ_LENGTH_UNIT; see the gmt.conf
man page for details. Choose one of the following projections (The E or C after projection names stands
for Equal-Area and Conformal, respectively):
CYLINDRICAL PROJECTIONS:
-Jclon0/lat0/scale or -JClon0/lat0/width (Cassini).
Give projection center lon0/lat0 and scale (1:xxxx or UNIT/degree).
-Jcyl_stere/[lon0/[lat0/]]scale or -JCyl_stere/[lon0/[lat0/]]width (Cylindrical Stereographic).
Give central meridian lon0 (optional), standard parallel lat0 (optional), and scale along parallel
(1:xxxx or UNIT/degree). The standard parallel is typically one of these (but can be any value):
• 66.159467 - Miller’s modified Gall
• 55 - Kamenetskiy’s First
• 45 - Gall’s Stereographic
• 30 - Bolshoi Sovietskii Atlas Mira or Kamenetskiy’s Second
• 0 - Braun’s Cylindrical
-Jj[lon0/]scale or -JJ[lon0/]width (Miller Cylindrical Projection).
Give the central meridian lon0 (optional) and scale (1:xxxx or UNIT/degree).
-Jm[lon0/[lat0/]]scale or -JM[lon0/[lat0/]]width (Mercator [C])
Give central meridian lon0 (optional), standard parallel lat0 (optional), and scale along parallel
(1:xxxx or UNIT/degree).
-Joparameters (Oblique Mercator [C]).
Typically used with -RLLx/LLy/URx/URyr or with projected coordinates. Specify one of:
-Jo[a|A]lon0/lat0/azimuth/scale or -JO[a|A]lon0/lat0/azimuth/width
Set projection center lon0/lat0, azimuth of oblique equator, and scale.
-Jo[b|B]lon0/lat0/lon1/lat1/scale or -JO[b|B]lon0/lat0/lon1/lat1/scale
Set projection center lon0/lat0, another point on the oblique equator lon1/lat1, and scale.
-Joc|Clon0/lat0/lonp/latp/scale or -JOc|Clon0/lat0/lonp/latp/scale
Set projection center lon0/lat0, pole of oblique projection lonp/latp, and scale. Give
scale along oblique equator (1:xxxx or UNIT/degree). The upper-case A|B|C to removes
enforcement of a northern hemisphere pole.
-Jq[lon0/[lat0/]]scale or -JQ[lon0/[lat0/]]width (Cylindrical Equidistant).
Give the central meridian lon0 (optional), standard parallel lat0 (optional), and scale (1:xxxx or
UNIT/degree). The standard parallel is typically one of these (but can be any value):
• 61.7 - Grafarend and Niermann, minimum linear distortion
• 50.5 - Ronald Miller Equirectangular
• 43.5 - Ronald Miller, minimum continental distortion
• 42 - Grafarend and Niermann
• 37.5 - Ronald Miller, minimum overall distortion
• 0 - Plate Carree, Simple Cylindrical, Plain/Plane Chart
-Jtlon0/[lat0/]scale or -JTlon0/[lat0/]width (Transverse Mercator [C])
Give the central meridian lon0, central parallel lat0 (optional), and scale (1:xxxx or
UNIT/degree).
-Juzone/scale or -JUzone/width (UTM - Universal Transverse Mercator [C]).
Give the UTM zone (A,B,1-60[C-X],Y,Z)) and scale (1:xxxx or UNIT/degree). Zones: If C-X not
given, prepend - or + to enforce southern or northern hemisphere conventions [northern if south >
0].
-Jy[lon0/[lat0/]]scale or -JY[lon0/[lat0/]]width (Cylindrical Equal-Area [E]).
Give the central meridian lon0 (optional), standard parallel lat0 (optional), and scale (1:xxxx or
UNIT/degree). The standard parallel is typically one of these (but can be any value):
• 50 - Balthasart
• 45 - Gall-Peters
• 37.0666 - Caster
• 37.4 - Trystan Edwards
• 37.5 - Hobo-Dyer
• 30 - Behrman
• 0 - Lambert (default)
CONIC PROJECTIONS:
-Jblon0/lat0/lat1/lat2/scale or -JBlon0/lat0/lat1/lat2/width (Albers [E]).
Give projection center lon0/lat0, two standard parallels lat1/lat2, and scale (1:xxxx or
UNIT/degree).
-Jdlon0/lat0/lat1/lat2/scale or -JDlon0/lat0/lat1/lat2/width (Conic Equidistant)
Give projection center lon0/lat0, two standard parallels lat1/lat2, and scale (1:xxxx or
UNIT/degree).
-Jllon0/lat0/lat1/lat2/scale or -JLlon0/lat0/lat1/lat2/width (Lambert [C])
Give origin lon0/lat0, two standard parallels lat1/lat2, and scale along these (1:xxxx or
UNIT/degree).
-Jpoly/[lon0/[lat0/]]scale or -JPoly/[lon0/[lat0/]]width ((American) Polyconic).
Give the central meridian lon0 (optional), reference parallel lat0 (optional, default =
equator), and scale along central meridian (1:xxxx or UNIT/degree).
AZIMUTHAL PROJECTIONS:
Except for polar aspects, -Rw/e/s/n will be reset to -Rg. Use -R<…>r for smaller regions.
-Jalon0/lat0[/horizon]/scale or -JAlon0/lat0[/horizon]/width (Lambert [E]).
lon0/lat0 specifies the projection center. horizon specifies the max distance from projection
center (in degrees, <= 180, default 90). Give scale as 1:xxxx or radius/lat, where radius is
distance in UNIT from origin to the oblique latitude lat.
-Jelon0/lat0[/horizon]/scale or -JElon0/lat0[/horizon]/width (Azimuthal Equidistant).
lon0/lat0 specifies the projection center. horizon specifies the max distance from projection
center (in degrees, <= 180, default 180). Give scale as 1:xxxx or radius/lat, where radius is
distance in UNIT from origin to the oblique latitude lat.
-Jflon0/lat0[/horizon]/scale or -JFlon0/lat0[/horizon]/width (Gnomonic).
lon0/lat0 specifies the projection center. horizon specifies the max distance from projection
center (in degrees, < 90, default 60). Give scale as 1:xxxx or radius/lat, where radius is
distance in UNIT from origin to the oblique latitude lat.
-Jglon0/lat0[/horizon]/scale or -JGlon0/lat0[/horizon]/width (Orthographic).
lon0/lat0 specifies the projection center. horizon specifies the max distance from projection
center (in degrees, <= 90, default 90). Give scale as 1:xxxx or radius/lat, where radius is
distance in UNIT from origin to the oblique latitude lat.
-Jglon0/lat0/altitude/azimuth/tilt/twist/Width/Height/scale or
-JGlon0/lat0/altitude/azimuth/tilt/twist/Width/Height/width (General Perspective).
lon0/lat0 specifies the projection center. altitude is the height (in km) of the viewpoint
above local sea level. If altitude is less than 10, then it is the distance from the center of
the earth to the viewpoint in earth radii. If altitude has a suffix r then it is the radius
from the center of the earth in kilometers. azimuth is measured to the east of north of view.
tilt is the upward tilt of the plane of projection. If tilt is negative, then the viewpoint is
centered on the horizon. Further, specify the clockwise twist, Width, and Height of the
viewpoint in degrees. Give scale as 1:xxxx or radius/lat, where radius is distance in UNIT from
origin to the oblique latitude lat.
-Jslon0/lat0[/horizon]/scale or -JSlon0/lat0[/horizon]/width (General Stereographic [C]).
lon0/lat0 specifies the projection center. horizon specifies the max distance from projection
center (in degrees, < 180, default 90). Give scale as 1:xxxx (true at pole) or lat0/1:xxxx
(true at standard parallel lat) or radius/lat (radius in UNIT from origin to the oblique
latitude lat). Note if 1:xxxx is used then to specify horizon you must also specify the lat as
+-90 to avoid ambiguity.
MISCELLANEOUS PROJECTIONS:
-Jh[lon0/]scale or -JH[lon0/]width (Hammer [E]).
Give the central meridian lon0 (optional) and scale along equator (1:xxxx or UNIT/degree).
-Ji[lon0/]scale or -JI[lon0/]width (Sinusoidal [E]).
Give the central meridian lon0 (optional) and scale along equator (1:xxxx or UNIT/degree).
-Jkf[lon0/]scale or -JKf[lon0/]width (Eckert IV) [E]).
Give the central meridian lon0 (optional) and scale along equator (1:xxxx or UNIT/degree).
-Jk[s][lon0/]scale or -JK[s][lon0/]width (Eckert VI) [E]).
Give the central meridian lon0 (optional) and scale along equator (1:xxxx or UNIT/degree).
-Jn[lon0/]scale or -JN[lon0/]width (Robinson).
Give the central meridian lon0 (optional) and scale along equator (1:xxxx or UNIT/degree).
-Jr[lon0/]scale -JR[lon0/]width (Winkel Tripel).
Give the central meridian lon0 (optional) and scale along equator (1:xxxx or UNIT/degree).
-Jv[lon0/]scale or -JV[lon0/]width (Van der Grinten).
Give the central meridian lon0 (optional) and scale along equator (1:xxxx or UNIT/degree).
-Jw[lon0/]scale or -JW[lon0/]width (Mollweide [E]).
Give the central meridian lon0 (optional) and scale along equator (1:xxxx or UNIT/degree).
NON-GEOGRAPHICAL PROJECTIONS:
-Jp[a]scale[/origin][r|z] or -JP[a]width[/origin][r|z] (Polar coordinates (theta,r))
Optionally insert a after -Jp [ or -JP] for azimuths CW from North instead of directions CCW from East
[Default]. Optionally append /origin in degrees to indicate an angular offset [0]). Finally, append r
if r is elevations in degrees (requires s >= 0 and n <= 90) or z if you want to annotate depth rather
than radius [Default]. Give scale in UNIT/r-unit.
-Jxx-scale[/y-scale] or -JXwidth[/height] (Linear, log, and power scaling)
Give x-scale (1:xxxx or UNIT/x-unit) and/or y-scale (1:xxxx or UNIT/y-unit); or specify width and/or
height in UNIT. y-scale=x-scale if not specified separately and using 1:xxxx implies that x-unit and
y-unit are in meters. Use negative scale(s) to reverse the direction of an axis (e.g., to have y be
positive down). Set height or width to 0 to have it recomputed based on the implied scale of the other
axis. Optionally, append to x-scale, y-scale, width or height one of the following:
d Data are geographical coordinates (in degrees).
l Take log10 of values before scaling.
ppower Raise values to power before scaling.
t Input coordinates are time relative to TIME_EPOCH.
T Input coordinates are absolute time.
For mixed axes with only one geographic axis you may need to set -f as well. Default axis lengths
(see gmt.conf) can be invoked using -JXh (for landscape); -JXv (for portrait) will swap the x- and
y-axis lengths. The default unit for this installation is either cm or inch, as defined in the
file share/gmt.conf. However, you may change this by editing your gmt.conf file(s).
When -J is used without any further arguments, or just with the projection type, the arguments of the
last used -J, or the last used -J with that projection type, will be used.
-Jz|Zparameters
Set z-axis scaling; same syntax as -Jx.
-K More PostScript code will be appended later [Default terminates the plot system]. Required for all
but the last plot command when building multi-layer plots.
-O Selects Overlay plot mode [Default initializes a new plot system]. Required for all but the first
plot command when building multi-layer plots.
-P Select “Portrait” plot orientation [Default is “Landscape”; see gmt.conf or gmtset to change the
PS_PAGE_ORIENTATION parameter, or supply --PS_PAGE_ORIENTATION=orientation on the command line].
-Rxmin/xmax/ymin/ymax[+r][+uunit]
xmin, xmax, ymin, and ymax specify the region of interest. For geographic regions, these limits
correspond to west, east, south, and north and you may specify them in decimal degrees or in
[+|-]dd:mm[:ss.xxx][W|E|S|N] format. Append +r if lower left and upper right map coordinates are
given instead of west/east/south/north. 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 -Rcodex0/y0/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 x0/y0 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. When -R is used without any further arguments, the values from the last use of -R
in a previous GMT command will be used. For calendar time coordinates you may either give (a)
relative time (relative to the selected TIME_EPOCH and in the selected TIME_UNIT; append t to
-JX|x), or (b) absolute time of the form [date]T[clock] (append T to -JX|x). At least one of date
and clock must be present; the T is always required. The date string must be of the form
[-]yyyy[-mm[-dd]] (Gregorian calendar) or yyyy[-Www[-d]] (ISO week calendar), while the clock
string must be of the form hh:mm:ss[.xxx]. The use of delimiters and their type and positions must
be exactly as indicated (however, input, output and plot formats are customizable; see gmt.conf).
You can also use Cartesian projected coordinates compatible with the chosen projection. Append
the length unit via the +u modifier, (e.g., -R-200/200/-300/300+uk for a 400 by 600 km rectangular
area centered on the projection center (0, 0). These coordinates are internally converted to the
corresponding geographic (longitude, latitude) coordinates for the lower left and upper right
corners. This form is convenient when you want to specify a region directly in the projected units
(e.g., UTM meters).
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.
-U[[just]/dx/dy/][c|label]
Draw Unix System time stamp on plot. By adding [just]/dx/dy/, the user may specify the
justification of the stamp and where the stamp should fall on the page relative to lower left
corner of the plot. For example, BL/0/0 will align the lower left corner of the time stamp with
the lower left corner of the plot [LL]. Optionally, append a label, or c (which will plot the
command string.). The GMT parameters MAP_LOGO, MAP_LOGO_POS, and FORMAT_TIME_STAMP can affect the
appearance; see the gmt.conf man page for details. The time string will be in the locale set by
the environment variable TZ (generally local time).
-V[level]
Select verbose mode, which will send progress reports to stderr. Choose among 6 levels of
verbosity; each level adds more messages: q - Complete silence, not even fatal error messages are
produced. n - Normal verbosity: produce only fatal error messages. c - Produce also
compatibility warnings (same as when -V is omitted). v - Produce also warnings and progress
messages (same as -V only). l - Produce also detailed progress messages. d - Produce also
debugging messages.
-X[a|c|f|r][x-shift[u]]
-Y[a|c|f|r][y-shift[u]]
Shift plot origin relative to the current origin by (x-shift,y-shift) and optionally append the
length unit (c, i, or p). You can prepend a to shift the origin back to the original position
after plotting, prepend c to center the plot on the center of the paper (optionally add shift),
prepend f to shift the origin relative to the fixed lower left corner of the page, or prepend r
[Default] to move the origin relative to its current location. If -O is used then the default
(x-shift,y-shift) is (r0), otherwise it is (r1i). When -X or -Y are used without any further
arguments, the values from the last use of that option in a previous GMT command will be used.
-a[col=]name[…]
Control how aspatial data are handled in GMT during input and output. Reading OGR/GMT-formatted
files: To assign certain aspatial data items to GMT data columns, give one or more comma-separated
associations col=name, where name is the name of an aspatial attribute field in a OGR/GMT file and
whose value we wish to use as data input for column col. In addition, to assign an aspatial value
to non-column data, you may specify col as D for distance, G for fill, I for ID, L for label, T
for text, W for pen, and Z for value [e.g., used to look up color via a CPT]. If you skip the
leading “col=” in the argument then we supply (and automatically increment) a column value
starting at 2. Writing OGR/GMT-formatted files: To write OGR/GMT-formatted files, give one or
more comma-separated associations col=name[:type], with an optional data type from DOUBLE, FLOAT,
INTEGER, CHAR, STRING, DATETIME, or LOGICAL [DOUBLE]. To extract information from GMT multisegment
headers encoded in the -Ddistance, -Gfill, -IID, -Llabel, -Ttext, -Wpen, or -Zvalue settings,
specify COL as D, G, I, L, T, W or Z, respectively; type will be set automatically. Finally, you
must append +ggeometry, where geometry is either POINT, LINE, or POLY. Optionally, prepend M for
multi-versions of these geometries. To force the clipping of features crossing the Dateline, use
upper-case +G instead. See GMT Appendix Q for details of the OGR/GMT file format.
-bi[ncols][type][w][+L|+B]
Select native binary input. Here, ncols is the number of data columns of given type, which must be
one of c (int8_t, aka char), u (uint8_t, aka unsigned char), h (int16_t, 2-byte signed int), H
(uint16_t, 2-byte unsigned int), i (int32_t, 4-byte signed int), I ((capital i) uint32_t, 4-byte
unsigned int), l ((lower case el) int64_t, 8-byte signed int), L (uint64_t, 8-byte unsigned int),
f (4-byte single-precision float), and d (8-byte double-precision float). In addition, use x to
skip ncols bytes anywhere in the record. For records with mixed types, simply append additional
comma-separated combinations of ncolst. Append w to any item to force byte-swapping.
Alternatively, append +L|B to indicate that the entire data file should be read as little- or
big-endian, respectively. The cumulative number of ncols may exceed the columns actually needed by
the program. If ncols is not specified we assume that type applies to all columns and that ncols
is implied by the expectation of the program. If the input file is netCDF, no -b is needed; simply
append ?var1/var2/… to the filename to specify the variables to be read.
-bo[ncols][type][w][+L|+B]
Select native binary output. Here, ncols is the actual number of data columns of type t, which
must be one of c, u, h, H, i, I (capital i), l (lower case elle), L, f, and d (see -bi). For a
mixed-type output record, append additional comma-separated combinations of ncols/t. Append w to
any item to force byte-swapping or +L|B for byte-swapping of the entire record. If ncols is not
specified we assume that t applies to all columns and that ncols is implied by the default output
of the program. Note: NetCDF file output is not supported.
-d[i|o]nodata
Control how user-coded missing data values are translated to official NaN values in GMT. For
input data we replace any value that equals nodata with NaN. For output data we replace any NaN
with the chosen nodata value. Use -di or -do to only affect input or output.
-dinodata
Examine all input columns and if any item equals nodata we interpret this value as a missing data
item and substitute the value NaN.
-donodata
Examine all output columns and if any item equals NAN we substitute it with the chosen missing
data value nodata.
-e[~]”pattern” | -e[~]/regexp/[i]
Only accept ASCII data records that contains the specified pattern. To reverse the search, i.e.,
to only accept data record that do not contain the specified pattern, use -e~. Should your pattern
happen to start with ~ you need to escape this character with a backslash [Default accepts all
data records]. For matching data records against extended regular expressions enclose the
expression in slashes. Append i for case-insensitive matching. For a list of such patterns, give
+ffile with one pattern per line. To give a single pattern starting with +f, escape it with a
backslash.
-f[i|o]colinfo
Specify the data types of input and/or output columns (time or geographical data). Specify i or o
to make this apply only to input or output [Default applies to both]. Give one or more columns (or
column ranges) separated by commas, or use -f multiple times (column ranges must be given in the
format start[:inc ]:stop, where inc defaults to 1 if not specified). Append T (absolute calendar
time), t (relative time in chosen TIME_UNIT since TIME_EPOCH), x (longitude), y (latitude),
p[unit] (projected x,y map coordinates in given unit [meter]) or f (floating point) to each column
or column range item. Shorthands -f[i|o]g means -f[i|o]0x,1y (geographic coordinates) and -f[i|o]c
means -f[i|o]0-1f (Cartesian coordinates)
-g[a]x|y|d|X|Y|D|[col]z[+|-]gap[u]
Examine the spacing between consecutive data points in order to impose breaks in the line. Append
x|X or y|Y to define a gap when there is a large enough change in the x or y coordinates,
respectively, or d|D for distance gaps; use upper case to calculate gaps from projected
coordinates. For gap-testing on other columns use [col]z; if col is not prepended the it defaults
to 2 (i.e., 3rd column). Append [+|-]gap and optionally a unit u. Regarding optional signs: -ve
means previous minus current column value must exceed gap to be a gap, +ve means current minus
previous column value must exceed gap, and no sign means the absolute value of the difference must
exceed gap. For geographic data (x|y|d), the unit u may be arc degree, minute, or second, or meter
[Default], foot, kilometer, Mile, nautical mile, or survey foot. For projected data (X|Y|D),
choose from inch, centimeter, or point [Default unit set by PROJ_LENGTH_UNIT]. Note: For x|y|z
with time data the unit is instead controlled by TIME_UNIT. Repeat the option to specify multiple
criteria, of which any can be met to produce a line break. Issue an additional -ga to indicate
that all criteria must be met instead.
-h[i|o][n][+c][+d][+rremark][+ttitle]
Primary input file(s) has header record(s). If used, the default number of header records is
IO_N_HEADER_RECS [1]. Use -hi if only the primary input data should have header records [Default
will write out header records if the input data have them]. Blank lines and lines starting with #
are always skipped. For output you may request additional headers to be written via the option
modifiers, and use +d to remove existing header records. Append +c to issue a header comment with
column names to the output [none]. Append +r to add a remark comment to the output [none].
Append +t to add a title comment to the output [none]. These optional strings may contain n to
indicate line-breaks). If used with native binary data we interpret n to instead mean the number
of bytes to skip on input or pad on output.
-icols[+l][+sscale][+ooffset][,…]
Select specific data columns for primary input, in arbitrary order. Columns not listed will be
skipped. Give individual columns (or column ranges in the format start[:inc ]:stop, where inc
defaults to 1 if not specified) separated by commas [Default reads all columns in order, starting
with the first column (0)]. Columns may be repeated. To each column, optionally add any of the
following: +l takes log10 of the input values first; +sscale, subsequently multiplies by a given
scale factor [1]; +ooffset, finally adds a given offset [0].
-n[b|c|l|n][+a][+bBC][+c][+tthreshold]
Select grid interpolation mode by adding b for B-spline smoothing, c for bicubic interpolation, l
for bilinear interpolation, or n for nearest-neighbor value (for example to plot categorical
data). Optionally, append +a to switch off antialiasing (where supported). Append +bBC to override
the boundary conditions used, adding g for geographic, p for periodic, or n for natural boundary
conditions. For the latter two you may append x or y to specify just one direction, otherwise both
are assumed. Append +c to clip the interpolated grid to input z-min/max [Default may exceed
limits]. Append +tthreshold to control how close to nodes with NaNs the interpolation will go. A
threshold of 1.0 requires all (4 or 16) nodes involved in interpolation to be non-NaN. 0.5 will
interpolate about half way from a non-NaN value; 0.1 will go about 90% of the way, etc. [Default
is bicubic interpolation with antialiasing and a threshold of 0.5, using geographic (if grid is
known to be geographic) or natural boundary conditions].
-ocols[,…]
Select specific data columns for primary output, in arbitrary order. Columns not listed will be
skipped. Give columns (or column ranges in the format start[:inc ]:stop, where inc defaults to 1
if not specified) separated by commas. Columns may be repeated. [Default writes all columns in
order].
-p[x|y|z]azim[/elev[/zlevel]][+wlon0/lat0[/z0]][+vx0/y0]
Selects perspective view and sets the azimuth and elevation of the viewpoint [180/90]. When -p is
used in consort with -Jz or -JZ, a third value can be appended which indicates at which z-level
all 2D material, like the plot frame, is plotted (in perspective). [Default is at the bottom of
the z-axis]. Use -px or -py to plot against the “wall” x = level or y = level (default is on the
horizontal plane, which is the same as using -pz). For frames used for animation, you may want to
append + to fix the center of your data domain (or specify a particular world coordinate point
with +wlon0/lat[/z]) which will project to the center of your page size (or specify the
coordinates of the projected view point with +vx0/y0. When -p is used without any further
arguments, the values from the last use of -p in a previous GMT command will be used.
Alternatively, you can perform a simple rotation about the z-axis by just giving the rotation
angle. Optionally, use +v or +w to select another axis location than the plot origin.
-r Force pixel node registration [Default is gridline registration]. (Node registrations are defined
in Section grid-registration of the GMT Technical Reference and Cookbook.)
-s[cols][a|r]
Suppress output for records whose z-value equals NaN [Default outputs all records]. Append a to
skip records where at least one field equal NaN. Append r to reverse the suppression, i.e., only
output the records whose z-value equals NaN. Alternatively, indicate a comma-separated list of all
columns or column ranges to consider for this NaN test (Column ranges must be given in the format
start[:inc ]:stop, where inc defaults to 1 if not specified).
-t[transp]
Set PDF transparency level for an overlay, in 0-100 percent range. [Default is 0, i.e., opaque].
-x[[-]n]
Limit the number of cores to be used in any OpenMP-enabled multi-threaded algorithms. By default
we try to use all available cores. Append n to only use n cores (if too large it will be
truncated to the maximum cores available). Finally, give a negative n to select (all - n) cores
(or at least 1 if n equals or exceeds all). The -x option is only available to GMT modules
compiled with OpenMP support.
-:[i|o]
Swap 1st and 2nd column on input and/or output [Default is no swapping]. Append i to select input
only or o to select output only. [Default affects both]. This option is typically used to handle
(latitude, longitude) files; see also -icols[l][sscale][ooffset][,…].
-^ 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.
Specifying Color
color The color of lines, areas and patterns can be specified by a valid color name, by a gray shade (in
the range 0-255), by a decimal color code (r/g/b, each in range 0-255; h-s-v, ranges 0-360, 0-1,
0-1; or c/m/y/k, each in range 0-1), or by a hexadecimal color code (#rrggbb, as used in HTML).
For PDF transparency, append @transparency in the 0-100 percent range [0 or opaque]. See gmtcolors
for more information and a full list of color names.
Specifying Fill
fill The attribute fill specifies the solid shade or solid color (see Specifying Color above) or the
pattern used for filling polygons. Patterns are specified as ppattern, where pattern set the
number of the built-in pattern (1-90) or the name of a raster image file. The optional +rdpi sets
the resolution of the image [1200]. For 1-bit rasters: use upper case P for inverse video, or
append +fcolor and/or +bcolor to specify fore- and background colors (use color = - for
transparency). See GMT Cookbook & Technical Reference Appendix E for information on individual
built-in patterns.
Specifying Fonts
font The attributes of text fonts as defined by font is a comma delimited list of size, fonttype and
fill, each of which is optional. size is the font size (usually in points) but c or i can be added
to indicate other units. fonttype is the name (case sensitive!) of the font or its equivalent
numerical ID (e.g., Helvetica-Bold or 1). fill specifies the gray shade, color or pattern of the
text (see Specifying Fill above). Optionally, you may append =pen to the fill value in order to
draw a text outline. If you want to avoid that the outline partially obscures the text, append
append =~pen instead; in that case only half the linewidth is plotted on the outside of the font
only. If an outline is requested, you may optionally skip the text fill by setting it to -, in
which case the full pen width is always used. If any of the font attributes is omitted their
default or previous setting will be retained.
The 35 available fonts are:
0. Helvetica
1. Helvetica-Bold
2. Helvetica-Oblique
3. Helvetica-BoldOblique
4. Times-Roman
5. Times-Bold
6. Times-Italic
7. Times-BoldItalic
8. Courier
9. Courier-Bold
10. Courier-Oblique
11. Courier-BoldOblique
12. Symbol
13. AvantGarde-Book
14. AvantGarde-BookOblique
15. AvantGarde-Demi
16. AvantGarde-DemiOblique
17. Bookman-Demi
18. Bookman-DemiItalic
19. Bookman-Light
20. Bookman-LightItalic
21. Helvetica-Narrow
22. Helvetica-Narrow-Bold
23. Helvetica-Narrow-Oblique
24. Helvetica-Narrow-BoldOblique
25. NewCenturySchlbk-Roman
26. NewCenturySchlbk-Italic
27. NewCenturySchlbk-Bold
28. NewCenturySchlbk-BoldItalic
29. Palatino-Roman
30. Palatino-Italic
31. Palatino-Bold
32. Palatino-BoldItalic
33. ZapfChancery-MediumItalic
34. ZapfDingbats
Specifying Pens
pen The attributes of lines and symbol outlines as defined by pen is a comma-delimited list of width,
color and style, each of which is optional. width can be indicated as a measure (in points (this
is the default), centimeters, or inches) or as faint, default, thin[ner|nest], thick[er|est],
fat[ter|test], or obese. color specifies a gray shade or color (see Specifying Color above). style
can be any of ‘solid’, ‘dashed’ or ‘dotted’, or a custom combination of dashes ‘-‘ and dots ‘.’.
If any of the attributes is omitted their default or previous setting will be retained. See GMT
Cookbook & Technical Reference Specifying pen attributes for more information.
ASCII FORMAT PRECISION
The ASCII output formats of numerical data are controlled by parameters in your gmt.conf file. Longitude
and latitude are formatted according to FORMAT_GEO_OUT, absolute time is under the control of
FORMAT_DATE_OUT and FORMAT_CLOCK_OUT, whereas general floating point values are formatted according to
FORMAT_FLOAT_OUT. Be aware that the format in effect can lead to loss of precision in ASCII output, which
can lead to various problems downstream. If you find the output is not written with enough precision,
consider switching to binary output (-bo if available) or specify more decimals using the
FORMAT_FLOAT_OUT setting.
GRID FILE FORMATS
By default GMT writes out grid as single precision floats in a COARDS-complaint netCDF file format.
However, GMT is able to produce and read grid files in many other commonly used grid file formats and
also facilitates so called “packing” of grids, writing out floating point data as 1- or 2-byte integers.
To specify the precision, scale and offset, the user should add the suffix =id[/scale/offset[/nan]],
where id is a two-letter identifier of the grid type and precision, and scale and offset are optional
scale factor and offset to be applied to all grid values, and nan is the value used to indicate missing
data. In case the two characters id is not provided, as in =/scale than a id=nf is assumed. When reading
grids, the format is generally automatically recognized from almost all of those formats that GMT and
GDAL combined offer. If not, the same suffix can be added to input grid file names. See grdconvert and
Section grid-file-format of the GMT Technical Reference and Cookbook for more information.
When reading a netCDF file that contains multiple grids, GMT will read, by default, the first
2-dimensional grid that can find in that file. To coax GMT into reading another multi-dimensional
variable in the grid file, append ?varname to the file name, where varname is the name of the variable.
Note that you may need to escape the special meaning of ? in your shell program by putting a backslash in
front of it, or by placing the filename and suffix between quotes or double quotes. The ?varname suffix
can also be used for output grids to specify a variable name different from the default: “z”. See
grdconvert and Sections modifiers-for-CF and grid-file-format of the GMT Technical Reference and Cookbook
for more information, particularly on how to read splices of 3-, 4-, or 5-dimensional grids.
SEE ALSO
Look up the individual man pages for more details and full syntax. Run gmt --help to list all GMT
programs and to show all installation directories. For an explanation of the various GMT settings in this
man page (like FORMAT_FLOAT_OUT), see the man page of the GMT configuration file gmt.conf. Information is
also available on the GMT home page http://gmt.soest.hawaii.edu/
COPYRIGHT
2018, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe