Provided by: gmt_6.0.0+dfsg-1build2_amd64 
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
Starts a given GMT module with the module-options that pertain to that particular module. A few
special commands are also available:
gmt clear items
Deletes current defaults, or the cache, data or sessions directories. Choose between defaults
(deletes the current gmt.conf file used for the current modern session), cache (deletes the user’s
cache directory and all of its content), data (deletes the user’s data download directory and all
of its content), or all (does all of the above).
gmt begin [session-prefix] [format] [options]
Initializes a new GMT session under modern mode [Default is classic mode]. All work is performed
in a temporary work directory. The optional session-prefix assigns a name to the session, and
this may be used as figure name for single-figure sessions [gmtsession]. Likewise, the optional
format can be used to override the default graphics format [PDF].
gmt figure prefix [format(s)] [options]
Specifies the desired name, output format(s) and any custom arguments that should be passed to
psconvert when producing this figure. All subsequent plotting will be directed to this current
figure until another gmt figure command is issued or the session ends. The prefix is used to
build final figure names when extensions are automatically appended. The format setting is a
comma-separated list of desired extensions (e.g., pdf,png).
gmt inset [arguments]
Allows users to place a map inset by temporarily changing where plotting takes place as well as
the region and projection, then resets to previous stage.
gmt subplot [arguments]
Allows users to create a matrix of panels with automatic labeling and advancement.
gmt end [show]
Terminates a GMT modern mode session and automatically converts the registered illustration(s) to
the specified formats, then eliminates the temporary work directory. The figures are placed in
the current directory.
If no module is given then several other options are available:
--help List and description of GMT modules.
--new-script[=L]
Write a GMT modern mode script template to stdout. Optionally append the desired scripting
language among bash, csh, or batch. Default is the main shell closest to your current shell
(e.g., bash for zsh, csh for tcsh).
--show-bindir
Show directory of executables and exit.
--show-citation
Show the citation for the latest GMT publication.
--show-cores
Show number of available cores.
--show-datadir
Show data directory/ies and exit.
--show-dataserver
Show URL of the remote GMT data server.
--show-doi
Show the DOI of the current release.
--show-modules
List module names on stdout and exit.
--show-library
Show the path of the shared GMT library.
--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 MODULES
Run gmt --help to print the list of all core and supplementals modules within GMT, and a very short
description of their purpose. Detailed information about each program can be found in the separate
manual pages.
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
-Rwest/east/south/north[/zmin/zmax][+r][+uunit]
-U[stamp]
-V[level]
-X[a|c|f|r][xshift[u]]
-Y[a|c|f|r][yshift[u]] -aflags -bbinary -dnodata -eregexp -fflags -ggaps -hheaders -iflags -jflags -n‐
flags -oflags -pflags -rreg -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 and ticks the specified axes. To just draw an
axis without annotation and ticks you can use the l(eft), r(ight), b(ottom), t(opt) and (for 3-D)
u(p) codes. If a 3-D basemap is selected with -p and -Jz, append Z, z, or u 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[+aangle|n|p][+l|Llabel][+pprefix][+uunit]
but you may also split this into two separate invocations for clarity, i.e.,
• -B[p|s][x|y|z][+aangle|n|p][+l|Llabel][+pprefix][+s|Sseclabel][+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). For Cartesian axes you may specify an alternate via +s which is
used for right or upper axis axis label (with any +l label used for left and bottom axes). 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. Cartesian x-axes also allow for the optional +aangle, which will plot
slanted annotations; angle is measured with respect to the horizontal and must be in the -90 <= angle
<= 90 range only. Also, +an is a shorthand for normal (i.e., +a90) and +ap for parallel (i.e., +a0)
annotations [Default]. For the y-axis, arbitrary angles are not allowed but +an and +ap specify
annotations normal [Default] and parallel to the axis, respectively. Note that these defaults can be
changed via MAP_ANNOT_ORTHO.
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 the ones listed below:
• 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 weekdays in selected language)
• k (weekday, plot number of day in the week (1–7) (see TIME_WEEK_START))
• 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.
Finally, if your axis is in radians you can use multiples or fractions of pi to set such annotation
intervals. The format is [n]pi[m], for an optional integer n and optional m fractions 2, 3, or 4.
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 +dh, +du, or +dl to the given width if you
instead want to set map height, the maximum (upper) dimension, or the minimum (lower) dimension,
respectively [Default is +dw 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). Use upper-case A|B|C to remove
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
• 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.
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.
-J<proj4>|EPSG:n
Starting at GMT6 it is possible to use the PROJ.4 library to do coordinate and datum transforms.
This is achieved via GDAL so it requires that GMT build is linked to that library. It is, however,
beyond the scope of this manual to document the PROJ.4 syntax (that is the syntax of the proj and
cs2cs programs) so users are referred to it http://proj4.org/apps/index.html for the details.
The usage of PROJ.4 follows very closely the syntax of proj and cs2cs. The projection parameters
are encapsulated under the -J option. Because there are normally several parameters defining a
referencing system separated by spaces (in PROJ.4 or GDAL) we can either use double quotes as in
-J”+proj=merc +ellps=WGS84 +units=m” or just glue all parameters like in
-J+proj=merc+ellps=WGS84+units=m.
Using EPSG codes is also possible (but need the setting of the GDAL_DATA environment variable to
point to the GDAL’s data sub-directory). For example -JEPSG:4326 sets the WGS-84 system.
For mapproject and grdproject we can go directly from the referencing system A to B without the
intermediate step of converting to geographic coordinates. That is obtained (like in cs2cs) by
using the +to keyword. Example: -JEPSG:4326+to+proj=aeqd+ellps=WGS84+units=m. A much awaited bonus
is also that we now do not need to set -R to do point coordinate conversions.
While for point and grid conversions done by mapproject and grdproject we can use all PROJ.4
projections, the situations is, however, rather more limited for mapping purposes. Here, only the
subset of the PROJ.4 projections that can be mapped into the GMT projections syntax is available
to use. Another aspect that is not present in PROJ.4, because it’s not a mapping library, is how
to set the map scale or map dimension. We introduced the two extensions +width=size and
+scale=1:xxxx that work exactly like the map width and scale in classical GMT. It is also allowed
to provide the scale (but NOT the width) by appending the string “/1:xxx” to the end of the
projection parameters.
-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). Set geographic regions
by specifying ISO country codes from the Digital Chart of the World using
-Rcode1,code2,…[+r|R[incs]] instead: Append one or more comma-separated countries using the
2-character ISO 3166-1 alpha-2 convention. To select a state of a country (if available), append
.state, e.g, US.TX for Texas. To specify a whole continent, prepend = to any of the continent
codes AF (Africa), AN (Antarctica), AS (Asia), EU (Europe), OC (Oceania), NA (North America), or
SA (South America). Use +r to modify the bounding box coordinates from the polygon(s): Append
inc, xinc/yinc, or winc/einc/sinc/ninc to adjust the region to be a multiple of these steps [no
adjustment]. Alternatively, use +R to extend the region outward by adding these increments instead
[no extension]. 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).
For Cartesian data in radians you can also use [±][s]pi[f], for optional integer scales s and
fractions f.
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[label][+c][+jjust][+odx/dy]
Draw the GMT Unix System time stamp on the plot. By appending +jjust and/or +odx/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, +jBL+o0/0 will align the lower left corner of the
time stamp with the bottom left corner of the plot [BL]. Optionally, append a label, or give +c
which will plot the command string. The GMT parameters MAP_LOGO, MAP_LOGO_POS, FONT_LOGO 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][xshift[u]]
-Y[a|c|f|r][yshift[u]]
Shift plot origin relative to the current origin by (xshift,yshift) 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. For overlays the default
(xshift,yshift) 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.
Note that -X and -Y can also access the previous plot dimensions w and h and construct offsets
that involves them. For instance, to move the origin up 2 cm beyond the height of the previous
plot, use -Yh+2c. To move the origin half the width to the right, use -Xw/2.
-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. Give just -a to select all aspatial items to be added to the input record.
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 format for primary input (secondary inputs are always ASCII). 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 ncols type
(no space). 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 type, which
must be one of c, u, h, H, i, I (capital i), l (lower case ell), L, f, and d (see -bi). For a
mixed-type output record, append additional comma-separated combinations of ncols type (no space).
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 type applies to all columns and that ncols is implied by the
default output of the program. Note: NetCDF file output is not supported.
-c[row,col |index]
Used to advance to the selected subplot panel. Only allowed when in subplot mode. Available to
all plot modules. If no arguments are given then we advance to the next panel in the selected
order. If no -c is given and we just entered subplot mode then the first panel (top, left) is
selected. Instead of row, col you may give the one-dimensional index which depends on the order
you set via -A when the subplot was defined. Note: row, col, and index all start at 0.
-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]zgap[u][+n|p]
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 and modifiers +n or +p. Here, +n
means previous minus current column value must exceed gap to be a gap and +p means current minus
previous column value must exceed gap. Otherwise 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][,…][,t[word]]
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]. Normally, any trailing text is read
but when i is used you must explicitly add the column t to retain the text. To only ingest a
single word from the trailing text, append the word number (first word is 0). Finally, -in will
simply read the numerical input and skip any trailing text.
-je|f|g
Determine how spherical distances are calculated in modules that support this. By default (-jg)
we perform great circle distance calculations and parameters such as distance increments or radii
will be compared against calculated great circle distances. To simplify and speed up calculations
you can select Flat Earth mode (-jf) which gives an approximate and fast result. Alternatively,
you can select ellipsoidal (-je) or geodesic mode for the highest precision (and slowest
calculation time). All spherical distance calculations depends on the current ellipsoid
(PROJ_ELLIPSOID), the definition of the mean radius (PROJ_MEAN_RADIUS), and the specification of
latitude type (PROJ_AUX_LATITUDE). Geodesic distance calculations is also controlled by method
(PROJ_GEODESIC).
-l[label][+dpen][+ffont][+ggap][+hheader][+jjust][+l[code/]txt][+ncols][+ssize][+v[pen]][+wwidth][+xscale]
[beta version] Add a map legend entry to the session legend information file for the current plot.
Optionally append a text label to describe the entry. Several modifiers allow further changes to
the legend (to be built when legend is called): Use +d to draw a horizontal line before the legend
entry is placed [no line], use +f to set the font used for the legend header [FONT_TITLE], use +g
to add some vertical space [0], use +h to add a legend header [no header], +j to set placement of
the legend [TR], use +l to set a line text; prepend a horizontal justification code L, C, or R
[C], use +n to change the number of columns used to set the following legend items [1], use +s to
override the size of the current symbol for the legend or set a length if plotting a line or
contour [same as plotted], use +v to start and +vpen to stop drawing vertical line from previous
to current horizontal line [no vertical line], use +w to set legend width [auto], and use +xscale
to resize all symbol and length sizes in the legend. Default pen is given by MAP_DEFAULT_PEN.
Note that +h, +j, +w, and +x will only take effect if given on the very first -l option for a
plot. The +n modifier, if used on the first -l option, affects the legend width (unless set via
+w); otherwise it just subdivides the available width among the specified columns. The automatic
legend has a fixed white background with a solid black pen outline and offset 0.2 cm from the map
frame. The modifiers largely reflect legend codes described in legend, which provide more details
and customization. If legend is not called explicitly we will call it implicitly when finishing
the plot via end.
-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[,…][t[word]]
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]. Normally, any trailing text in the internal records will be written but when -o is used
you must explicitly add the column t. To only output a single word from the trailing text, append
the word number (first word is 0). Finally, -on will simply write the numerical output only and
skip any trailing text. Note: If -i is also used then columns given to -o correspond to the order
after the -i selection and not the columns in the original record.
-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, note we fix the
center of your data domain. Specify another center using a particular world coordinate point with
+wlon0/lat0[/z0]) which will project to the center of your page size, or specify the coordinates
of the projected 2-D 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[g|p]
Force gridline or pixel node registration [Just -r sets pixel registration]. If no -r is given
then gridline registration is selected. (Node registrations are defined in Section option_nodereg
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, or 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 transparency level for an overlay, in (0-100] percent range. [Default is 0, i.e., opaque].
Only visible when PDF or raster format output is selected.
-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.
--PAR=value
Temporarily override a GMT default setting; repeatable. See /gmt.conf for parameters.
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 transparency, append @transparency in the 0-100 percent range [0 or opaque] (Only visible when
PDF or raster format output is selected.). 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 (plus 4 optional Japanese 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
35. Ryumin-Light-EUC-H
36. Ryumin-Light-EUC-V
37. GothicBBB-Medium-EUC-H
38. GothicBBB-Medium-EUC-V
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’ ‘dotted’, ‘dashdot’, or ‘dotdash’, 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 grids 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][+sscale][+ooffset][+ninvalid], where id is a two-letter identifier of the grid type and precision,
and the scale, offset and invalid are the arguments of optional modifiers to be applied to all grid
values, Here, invalid is the value used to indicate missing data. In case the id is not provided, as in
+sscale 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.
CLASSIC MODE OPTIONS
These options are only used in classic mode and are listed here just for reference.
-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].
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 documentation site https://docs.generic-mapping-tools.org/
COPYRIGHT
2019, The GMT Team.