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gmt(1)                                GMT                               gmt(1)



## NAME

       gmt  -  The  Generic Mapping Tools data processing and display software
package



## INTRODUCTION

       GMT is a collection of freely available command-line  tools  under  the
GNU LGPL that allows you to manipulate x,y and x,y,z data sets (filter-
ing, trend fitting, gridding, projecting, etc.) and  produce  illustra-
tions  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  direc-
tories.   Choose  between defaults (deletes the current gmt.conf
file used for the current modern session),  cache  (deletes  the
useras  cache  directory  and all of its content), data (deletes
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 direc-
tory.   The  optional  session-prefix assigns a name to the ses-
sion, and this may be used as figure name for single-figure ses-
sions  [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  cur-
rent  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 label-

gmt end [show]
Terminates a GMT modern mode session and automatically  converts
the  registered illustration(s) to their specified formats, then
eliminates the temporary work directory.  The figures are placed
in the current directory.

For  information  on  any module, load the module documentation in your
browser via gmt docs, e.g.:

gmt docs grdimage

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).

--new-glue=name
Write  the  C code glue needed when building third-party supple-
ments as shared libraries.  The name is the name of  the  shared
library. Run gmt in the directory of the supplement and the glue
code will be written to stdout.   Including  this  C  code  when
building the shared library means gmt can list available modules
via the --show-modules, --help options.  We recommend saving the
code to gmt_name_glue.c.

--show-bindir
Show directory of executables and exit.

--show-citation
Show the citation for the latest GMT publication.

--show-classic
List classic module names on stdout and exit.

--show-classic-core
List classic module names (core only) on stdout and exit.

--show-cores
Show number of available cores.

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 modern module names on stdout and exit.

--show-modules-core
List modern module names (core only) 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.

--show-userdir
Show full path of useras ~/.gmt dir 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  distri-
bution,  you  may  still  need  to  source the gmt completion file from
mand-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 from the GMT infrastructure  and  extend  GMT  in  specific
ways.



## THE COMMON GMT OPTIONS

       -B[p|s]parameters              -Jparameters             -Jz|Zparameters
-Rwest/east/south/north[/zmin/zmax][+r][+uunit]   -U[stamp]   -V[level]
-X[a|c|f|r][xshift]    -Y[a|c|f|r][yshift]    -aflags    -bbinary   -c-
row,col|index -dnodata -eregexp -fflags -ggaps  -hheaders  -iflags  -j-
flags  -lflags  -nflags  -oflags -pflags -qflags -rreg -sflags -ttransp
-x[[-]n] -:[i|o]



## DESCRIPTION

       These are all the common GMT options that remain the same for  all  GMT
modules. No space between the option flag and the associated arguments.

The -B option
Syntax

-B[p|s]parameters
Set map boundary frame and axes attributes. (See cookbook infor-
mation).

Description

This  is potentially the most complicated option in GMT, but most exam-
ples of its usage are actually quite simple. We distinguish between two
sets  of  information: Frame settings and Axes settings.  These are set
separately by their own -B invocations; hence  multiple  -B  specifica-
tions  may  be specified. The Frame settings cover things such as which
axes should be plotted, canvas fill, plot  title  (and  subtitle),  and
what  type  of  gridlines be drawn, whereas the Axes settings deal with
annotation, tick, and gridline intervals, axes labels,  and  annotation
units.

Frame settings
The Frame settings are specified by
-B[axes][+b][+gfill][+i[val]][+n][+olon/lat][+ssubtitle][+tti-
tle][+w[pen]][+xfill][+yfill][+zfill]

The frame setting is optional but can be invoked once to  override  the
defaults.  The following modifiers can be appended to -B to control the
Frame settings:

o axes to set which of the axes should be drawn and possibly  annotated
using  a  combination  of  the  codes  listed below [default is theme
dependent]. Borders omitted from the set of codes will not be  drawn.
For  example,  WSn  denotes  that the awesterna (left) and asoutherna
(bottom) axes should be drawn  with  tick-marks  and  annotations  by
using  W  and S; that the anortherna (top) edge of the plot should be
drawn with tick-marks and without annotations by using  n;  and  that
the  aeasterna  (right) axes should not be drawn by not including one
of E|e|r.

o West, East, South, North, and/or (for 3-D plots) Z indicate axes
that should be drawn with both tick-marks and annotations.

o west, east, south, north, and/or (for 3-D plots) z indicate axes
that should be drawn with tick-marks but without annotations.

o l(eft), r(ight), b(ottom), t(op) and/or  (for  3-D  plots)  u(p)
indicate axes that should be drawn without tick-marks or annota-
tions.

o Z|zcode (for 3-D plots) where code is any combination of  the  corner
ids  1,  2, 3, 4.  By default, a single vertical axes will be plotted
for 3-D plots at the most suitable map corner. code can  be  used  to
override this, where 1 represents the south-western (lower-left) cor-
ner,  2  the  south-eastern  (lower-right),   3   the   north-eastern
(upper-right), and 4 the north-western (upper-left) corner.

o +w[pen]  (for  3-D  plots)  to  draw  the outlines of the x-z and y-z
planes [default is no outlines]. Optionally, append  pen  to  specify
different pen attributes [default is MAP_GRID_PEN_PRIMARY].

o +b  (for  3-D  plots)  to  draw  the foreground lines of the 3-D cube
defined by -R.

o +gfill to paint the interior of the canvas with a color specified  by
fill [default is no fill]. This also sets fill for the two back-walls
in 3-D plots.

o +xfill to paint the yz plane with a color specified by fill  [default
is no fill].

o +yfill  to paint the xz plane with a color specified by fill [default
is no fill].

o +zfill to paint the xy plane with a color specified by fill  [default
is no fill].

o +i[val]  to  annotate  an internal meridian or parallel when the axis
that normally would be drawn and annotated does not exist (e.g.,  for
an azimuthal map with 360-degree range that has no latitude axis or a
global Hammer map that has no longitude axis). val gives the meridian
or parallel that should be annotated [default is 0].

o +olon/lat  to  produce oblique gridlines about another pole specified
by lon/lat [default references to the North pole]. +o is  ignored  if
no gridlines are requested.

o +n  to  have no frame and annotations at all [default is contolled by
axes].

o +ttitle to place the string given in title centered  above  the  plot
frame [default is no title].

o +ssubtitle  (requires  +ttitle) to place the string given in subtitle
beneath the title [default is no subtitle].

Note: Both +ttitle and +ssubtitle may be set  over  multiple  lines  by
breaking  them  up  using  the markers @^ or <break>.  To include LaTeX
code as part of a single-line title or subtitle, enclose the expression
with  @[  markers  (or alternatively $a|$) (requires latex
and dvips to be installed). See  the  /cookbook/gmt-latex  chapter  for
more details.

Axes settings
The Axes settings are specified by
-B[p|s][x|y|z]intervals[+aangle|n|p][+f][+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][+f][+l|Llabel][+pprefix][+s|Sseclabel][+uunit]
-B[p|s][x|y|z]intervals

The following modifiers can be appended to -B to control the Axes  set-
tings:

o p|s   to  set  whether  the  modifiers  apply  to  the  p(rimary)  or
s(econdary) axes [Default is p].  These settings are mostly used  for
time  axes annotations but are available for geographic axes as well.
Note: Primary refers to annotations closest to the axis and secondary
to  annotations further away.  Hence, primary annotation-, tick-, and
gridline-intervals must be shorter than their secondary counterparts.
The  terms  aprimarya and asecondarya do not reflect any hierarchical
order of units: the aprimarya annotation interval is usually  smaller
(e.g.,  days)  while the asecondarya annotation interval typically is
larger (e.g., months).

o x|y|z to set which axes the modifiers apply to [default  is  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.  For  a
3-D plot with the -p and -Jz options used, -Bz can be used to provide
settings for the verical axis.

o +f (for geographic axes only) to give fancy annotations with  W|E|S|N
suffices encoding the sign.

o +l|+Llabel  (for  Cartesian plots only) to add a label to an axis. +l
uses the default label orientation; +L forces a horizontal label  for
y-axes, which is useful for very short labels.

o +s|Sseclabel (for Cartesion plots only) to specify an alternate label
for the right or upper axes.  +s uses the default label  orientation;
+S  forces  a  horizontal  label for y-axes, which is useful for very
short labels.

o +pprefix (for Cartesion plots only) to define a leading  text  prefix
for  the  axis  annotation  (e.g.,  dollar  sign for plots related to
money). For geographic maps the addition of degree symbols,  etc.  is
automatic and controlled by FORMAT_GEO_MAP.

o +uunit  (for  Cartesion  plots  only) to append specific units to the
annotations. For geographic maps the addition of degree symbols, etc.
is automatic and controlled by FORMAT_GEO_MAP.

o +aangle (for Cartesion plots only) to plot slanted annotations, where
angle is measured with respect to the horizontal and must be  in  the
-90  <=  angle <= 90 range. +an can be used as a shorthand for normal
(i.e., +a90) [Default for y-axis] and +ap for  parallel  (i.e.,  +a0)
annotations  [Default  for x-axis]. These defaults can be changed via
MAP_ANNOT_ORTHO.

o intervals to define the intervals  for  annotations  and  major  tick
spacing,  minor tick spacing, and/or grid line spacing. See Intervals
Specification for the formatting associated with this modifier.

NOTE: To include LaTeX code as part of a label, enclose the  expression
with  @[  markers (or alternatively $a|$). (requires latex
and dvips to be installed). See  the  /cookbook/gmt-latex  chapter  for
more details.

NOTE: If any labels, prefixes, or units contain spaces or special char-
acters you will need to enclose them in quotes.

NOTE: Text items such as title, subtitle, label and seclabel  are  seen
by  GMT  as  part  of a long string containing everything passed to -B.
Therefore, they cannot contain substrings that look  like  other  modi-
fiers.  If  you  need to embed such sequences (e.g., +taSolving a+b=ca)
you need to replace those + symbols with their octal  equivalent  \053,
(e.g., +taSolving a\053b=ca).

NOTE: 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).
Intervals specification
The intervals specification is a concatenated string made up of substrings of the form

[a|f|g][stride][phase][unit].

The  choice of a|f|g sets the axis item of interest, which are detailed
in the Table interval types. Optionally,  append  phase  to  shift  the
annotations  by  that  amount (positive or negative with the sign being
required). Optionally, append unit to  specify  the  units  of  stride,
where  unit  is  one of the 18 supported unit codes. For custom annota-
tions and intervals, intervals can be given as cintfile, where  intfile
contains any number of records with coord type [label]. See the section
Custom axes for more details.

+-----+----------------------------+
|Flag | Description                |
+-----+----------------------------+
|a    | Annotation and major  tick |
|     | spacing                    |
+-----+----------------------------+
|f    | Minor tick spacing         |
+-----+----------------------------+
|g    | Grid line spacing          |
+-----+----------------------------+

NOTE:  The  appearance  of certain time annotations (month-, week-, and
day-names)  may  be  affected  by  the  GMT_LANGUAGE,  FORMAT_TIME_PRI-
MARY_MAP, and FORMAT_TIME_SECONDARY_MAP settings.

Automatic intervals: GMT will auto-select the spacing between the anno-
tations and major ticks, minor ticks, and grid lines if stride  is  not
provided  after a|f|g. This can be useful for automated plots where the
region may not always be the same, making it difficult to determine the
appropriate stride in advance. For example, -Bafg will select all three
spacings automatically for both axes.  In  case  of  longitudealatitude
plots,  this  will keep the spacing the same on both axes. You can also
use -Bxafg -Byafg to auto-select them separately. Note that  given  the
myriad  ways  of specifying time-axis annotations, the automatic selec-
tions may need to be overridden with manual settings to achieve exactly
what you need. When stride is omitted after g, the grid line are spaced
the same as the minor ticks; unless g is used in  consort  with  a,  in
which case the grid lines are spaced the same as the annotations.

Stride  units:  The  unit  flag  can  take on one of 18 codes which are
listed in Table Units. Almost all of these  units  are  time-axis  spe-
cific.  However,  the  d,  m,  and  s  units will be interpreted as arc
degrees, minutes, and arc seconds respectively when a map projection is
in effect.

+-----+----------------+---------------------+
|Flag | Unit           | Description         |
+-----+----------------+---------------------+

|Y    | year           | Plot  using  all  4 |
|     |                | digits              |
+-----+----------------+---------------------+
|y    | year           | Plot using  last  2 |
|     |                | digits              |
+-----+----------------+---------------------+
|O    | month          | Format   annotation |
|     |                | using          FOR- |
|     |                | MAT_DATE_MAP        |
+-----+----------------+---------------------+
|o    | month          | Plot   as   2-digit |
|     |                | integer (1a12)      |
+-----+----------------+---------------------+
|U    | ISO week       | Format   annotation |
|     |                | using          FOR- |
|     |                | MAT_DATE_MAP        |
+-----+----------------+---------------------+
|u    | ISO week       | Plot   as   2-digit |
|     |                | integer (1a53)      |
+-----+----------------+---------------------+
|r    | Gregorian week | 7-day  stride  from |
|     |                | start of week  (see |
|     |                | TIME_WEEK_START)    |
+-----+----------------+---------------------+
|K    | ISO weekday    | Plot  name of week- |
|     |                | day   in   selected |
|     |                | language            |
+-----+----------------+---------------------+
|k    | weekday        | Plot  number of day |
|     |                | in the  week  (1a7) |
|     |                | (see                |
|     |                | TIME_WEEK_START)    |
+-----+----------------+---------------------+
|D    | date           | Format   annotation |
|     |                | using          FOR- |
|     |                | MAT_DATE_MAP        |
+-----+----------------+---------------------+
|d    | day            | Plot day  of  month |
|     |                | (1a31)  or  day  of |
|     |                | year  (1a366)  (see |
|     |                | FORMAT_DATE_MAP)    |
+-----+----------------+---------------------+
|R    | day            | Same  as d; annota- |
|     |                | tions aligned  with |
|     |                | week           (see |
|     |                | TIME_WEEK_START)    |
+-----+----------------+---------------------+
|H    | hour           | Format   annotation |
|     |                | using          FOR- |
|     |                | MAT_CLOCK_MAP       |
+-----+----------------+---------------------+
|h    | hour           | Plot   as   2-digit |
|     |                | integer (0a24)      |
+-----+----------------+---------------------+
|M    | minute         | Format   annotation |
|     |                | using          FOR- |
|     |                | MAT_CLOCK_MAP       |
+-----+----------------+---------------------+
|m    | minute         | Plot   as   2-digit |
|     |                | integer (0a60)      |
+-----+----------------+---------------------+
|S    | seconds        | Format   annotation |
|     |                | using          FOR- |
|     |                | MAT_CLOCK_MAP       |
+-----+----------------+---------------------+

|s    | seconds        | Plot   as   2-digit |
|     |                | integer (0a60)      |
+-----+----------------+---------------------+

NOTE:  If your axis is in radians you can use multiples or fractions of
pi to set such annotation intervals. The format  is  [s]pi[f],  for  an
optional  integer  scale  s  and  optional integer fraction f. When GMT
parses one of these forms we alert the labeling machinery to  look  for
certain  combinations  of  pi, limited to npi, 3/2 pi (3pi2), and frac-
tions 3/4 (3pi4), 2/3 (2pi3), 1/2 (1pi2), 1/3 (1pi3), and 1/4 (1pi4) in
the interval given to the -B axes settings.  When an annotated value is
within roundoff-error of these combinations we typeset the label  using
the Greek letter \pi and required multiples or fractions.

NOTE:  These GMT parameters can affect the appearance of the map bound-
ary:
MAP_ANNOT_MIN_ANGLE,  MAP_ANNOT_MIN_SPACING, FONT_ANNOT_PRIMARY,
FONT_ANNOT_SECONDARY,  MAP_ANNOT_OFFSET_PRIMARY,  MAP_ANNOT_OFF-
SET_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, FOR-
MAT_CLOCK_MAP,  FORMAT_DATE_MAP,  FORMAT_TIME_PRIMARY_MAP,  FOR-
MAT_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.

The -J option
Syntax

-Jparameters
Specify  the projection. (See cookbook summary) (See projections
table).

Description

Select map projection. The first character of parameters determines the
projection.  If  the  character is upper case then the argument(s) sup-
plied 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). The measurement unit (called UNIT below) 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 the map height, the maximum  (upper)  dimen-
sion,  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 map projections is user-definable. 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
and  append  the required parameters (The E or C after projection names
stands for Equal-Area and Conformal, respectively):
CYLINDRICAL PROJECTIONS:
-Jc|Clon0/lat0/scale|width (Cassini).
Give projection center lon0/lat0 and either scale (with -Jc;  as
1:xxxx or plot-units/degree) or width (with -JC; in plot-units).
-Jcyl_stere|Cyl_stere/[lon0/[lat0/]]scale|width (Cylindrical Stereo-
graphic)
Give  central  meridian  lon0 (optional), standard parallel lat0
(optional), and either scale along parallel  (with  -Jcyl_stere;
as  1:xxxx  or plot-units/degree) or width (with -JCyc_stere; in
plot-units). The standard parallel is  typically  one  of  these
(but can be any value):

o 66.159467 - Milleras modified Gall

o 55 - Kamenetskiyas First

o 45 - Gallas Stereographic

o 30 - Bolshoi Sovietskii Atlas Mira or Kamenetskiyas Second

o 0 - Braunas Cylindrical
-Jj|J[lon0/]scale|width (Miller Cylindrical Projection).
Give the central meridian lon0 (optional) and either scale (with
-Jj; as 1:xxxx or plot-units/degree)  or  width  (with  -JJ;  in
plot-units).
-Jm|M[lon0/[lat0/]]scale|width (Mercator [C])
Give  central  meridian  lon0 (optional), standard parallel lat0
(optional), and either scale along parallel (with -Jm; as 1:xxxx
or plot-units/degree) or width (with -JM; in plot-units).
-Joparameters[+v] (Oblique Mercator [C]).
Typically  used with -RLLx/LLy/URx/URy+r or with projected coor-
dinates.  Specify one of:

-Jo|O[a|A]lon0/lat0/azimuth/scale|width[+v]
Set projection center lon0/lat0, azimuth of oblique equa-
tor, and scale or width

-Jo|O[b|B]lon0/lat0/lon1/lat1/scale|width[+v]
Set  projection  center  lon0/lat0,  another point on the
oblique equator lon1/lat1, and scale or width

-Jo|O[c|C]lon0/lat0/lonp/latp/scale|width[+v]
Set projection center lon0/lat0, pole of oblique  projec-
tion lonp/latp, and scale or width

Give  scale  along  oblique  equator  (with  -Ja|b|c;  1:xxxx or
plot-units/degree) or width (with -JA|B|C; in  plot-units).  Use
upper-case  A|B|C to remove enforcement of a northern hemisphere
pole. Append +v to let the oblique Equator align with the y-axis
[x-axis].  Note: If the region (-R) is given without the +r mod-
ifier then the arguments are considered oblique degrees relative
to the projection center and not longitude/latitude bounds.
-Jq|Q[lon0/[lat0/]]scale|width (Cylindrical Equidistant).
Give  the  central  meridian  lon0 (optional), standard parallel
lat0 (optional), and  either  scale  (with  -Jq;  as  1:xxxx  or
plot-units/degree)  or width (with -JQ; in plot-units) The stan-
dard parallel is typically one of these (but can be any value):

o 61.7 - Grafarend and Niermann, minimum linear distortion

o 50.5 - Ronald Miller Equirectangular

o 43.5 - Ronald Miller, minimum continental distortion

o 42 - Grafarend and Niermann

o 37.5 - Ronald Miller, minimum overall distortion

o 0 - Plate Carree, Simple Cylindrical, Plain/Plane Chart
-Jt|Tlon0/[lat0/]scale|width (Transverse Mercator [C])
Give  the  central  meridian   lon0,   central   parallel   lat0
(optional),   and   either   scale   (with  -Jt;  as  1:xxxx  or
plot-units/degree) or width (with -JT; in plot-units).
-Ju|Uzone/scale|width (UTM - Universal Transverse Mercator [C]).
Give the UTM zone (A,B,1-60[C-X],Y,Z)) and  either  scale  (with
-Ju;  as  1:xxxx  or  plot-units/degree)  or width (with -JU; in
plot-units). Zones: If C-X not given, prepend - or + to  enforce
southern or northern hemisphere conventions [default is northern
if south > 0].
-Jy|Y[lon0/[lat0/]]scale|width (Cylindrical Equal-Area [E]).
Give the central meridian  lon0  (optional),  standard  parallel
lat0  (optional),  and  either  scale  (with  -Jy;  as 1:xxxx or
plot-units/degree) or width (with -JY; in plot-units). The stan-
dard parallel is typically one of these (but can be any value):

o 50 - Balthasart

o 45 - Gall

o 37.0666 - Caster

o 37.4 - Trystan Edwards

o 37.5 - Hobo-Dyer

o 30 - Behrman

o 0 - Lambert (default)

CONIC PROJECTIONS:

-Jb|Blon0/lat0/lat1/lat2/scale|width (Albers [E]).
Give  projection  center  lon0/lat0,  two  standard parallels
lat1/lat2,  and  either  scale  (with  -Jb;  as   1:xxxx   or
plot-units/degree) or width (with -JB; in plot-units).

-Jd|Dlon0/lat0/lat1/lat2/scale|width (Conic Equidistant)
Give  projection  center  lon0/lat0,  two  standard parallels
lat1/lat2,  and  either  scale  (with  -Jd;  as   1:xxxx   or
plot-units/degree) or width (with -JD; in plot-units).

-Jl|Llon0/lat0/lat1/lat2/scale|width (Lambert [C])
Give  origin lon0/lat0, two standard parallels lat1/lat2, and
scale along these (with -Jl; as 1:xxxx or  plot-units/degree)
or width (with -JL; in plot-units).

-Jpoly|Poly/[lon0/[lat0/]]scale|width ((American) Polyconic).
Give the central meridian lon0 (optional), reference parallel
lat0 (optional, default = equator), and  either  scale  along
central    meridian    (with    -Jpoly;    as    1:xxxx    or
plot-units/degree) or width (with -JPoly; in plot-units).

AZIMUTHAL PROJECTIONS:

Except for polar aspects,  -Rw/e/s/n  will  be  reset  to  -Rg.  Use
-Rxlleft/ylleft/xuright/yuright+r for smaller regions.

-Ja|Alon0/lat0[/horizon]scale|width (Lambert [E]).
lon0/lat0  specifies the projection center. horizon specifies
the max distance from projection center (in degrees, <=  180,
default  90).  Give  either  scale  (with  -Ja;  as 1:xxxx or
gin  to  the  oblique  latitude  lat)  or width (with -JA; in
plot-units).

-Je|Elon0/lat0[/horizon]scale|width (Azimuthal Equidistant).
lon0/lat0 specifies the projection center. horizon  specifies
the  max distance from projection center (in degrees, <= 180,
default 180). Give scale (with -Je; as 1:xxxx or  radius/lat,
where  radius  is  distance  in plot-units from origin to the
oblique latitude lat) or width (with -JE; in plot-units).

-Jf|Flon0/lat0[/horizon]scale|width (Gnomonic).
lon0/lat0 specifies the projection center. horizon  specifies
the  max  distance  from projection center (in degrees, < 90,
default 60). Give scale (with -Jf; as 1:xxxx  or  radius/lat,
where  radius  is  distance  in plot-units from origin to the
oblique latitude lat) or width (with -JF; in plot-units).

-Jg|Glon0/lat0[/horizon]/scale|width (Orthographic).
lon0/lat0 specifies the projection center. horizon  specifies
the  max  distance from projection center (in degrees, <= 90,
default 90). Give scale (with -Jg; as 1:xxxx  or  radius/lat,
where  radius  is  distance  in plot-units from origin to the
oblique latitude lat.

-Jg|Glon0/lat0/altitude/azimuth/tilt/twist/Width/Height/scale|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 alti-
tude 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  pro-
jection.  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 (with -Jg;
plot-units  from origin to the oblique latitude lat) or width
(with -JG; in plot-units).

-Js|Slon0/lat0[/horizon]/scale|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 (with -Js; as 1:xxxx (true  at  pole)
or  lat0/1:xxxx (true at standard parallel lat) or radius/lat
(radius in plot-units 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.)  or  width
(with -JS; in plot-units).

MISCELLANEOUS PROJECTIONS:

-Jh|H[lon0/]scale|width (Hammer [E]).
Give  the  central  meridian lon0 (optional) and either scale
along equator (with -Jh; as 1:xxxx or  plot-units/degree)  or
width (with -JH; in plot-units).

-Ji|I[lon0/]scale|width (Sinusoidal [E]).
Give  the  central  meridian lon0 (optional) and either scale
along equator (with -Ji; as 1:xxxx or  plot-units/degree)  or
width (with -JI; in plot-units).

-Jk|Kf[lon0/]scale|width (Eckert IV [E]).
Give  the  central  meridian lon0 (optional) and either scale
along equator (with -Jk; as 1:xxxx or  plot-units/degree)  or
width (with -JK; in plot-units).

-Jk|K[s][lon0/]scale|width (Eckert VI [E]).
Give  the  central  meridian lon0 (optional) and either scale
along equator (with -Jk; as 1:xxxx or  plot-units/degree)  or
width (with -JK; in plot-units).

-Jn|N[lon0/]scale|width (Robinson).
Give  the  central  meridian lon0 (optional) and either scale
along equator (with -Jn; as 1:xxxx or  plot-units/degree)  or
width (with -JN; in plot-units).

-Jr|R[lon0/]scale|width (Winkel Tripel).
Give  the  central  meridian lon0 (optional) and either scale
along equator (with -Jr; as 1:xxxx or  plot-units/degree)  or
width (with -JR; in plot-units).

-Jv|V[lon0/]scale|width (Van der Grinten).
Give  the  central  meridian lon0 (optional) and either scale
along equator (with -Jv; as 1:xxxx or  plot-units/degree)  or
width (with -JV; in plot-units).

-Jw|W[lon0/]scale|width (Mollweide [E]).
Give  the  central  meridian lon0 (optional) and either scale
along equator (with -Jw; as 1:xxxx or  plot-units/degree)  or
width (with -JW; in plot-units).

NON-GEOGRAPHICAL PROJECTIONS:

Give scale (with -Jp; in plot-units/r-unit) or width (with  -JP;  in
plot-units). The following modifiers are supported by -Jp|P:

o +a  to  indicate  that  theta  is azimuth CW from North instead of
direction CCW from East [Default is CCW from East].

o +f to flip the radial direction to point inwards, and append e  to
indicate  that  r represents elevations in degrees (requires south
>= 0 and north <=  90),  p  to  select  current  planetary  radius
(determined  by  PROJ_ELLIPSOID)  as  maximum  radius  [north], or

o +k sets the annotation kind to be longitudes (x) or latitudes  (y)
[Default is unspecified angles].

o +roffset  to include a radial offset in measurement units [default
is 0].

o +torigin in degrees so that this angular value is aligned with the
positive  x-axis  (or  the azimuth to be aligned with the positive
y-axis if +a) [default is 0].

Alternatively,  if  your  r  data are actually depths then you can
-Jx|Xx-scale|width[l|ppower|T|t][/y-scale|height[l|ppower|T|t]][d|g]
(Linear, log, and power scaling)

Give x-scale (with  -Jx;  as  1:xxxx  or  plot-units/x-unit)  and/or
y-scale  (1:xxxx  or  plot-units/y-unit);  or  specify  width and/or
height (with -JX; in plot-units). 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.  Option-
ally,  append to x-scale y-scale, width or height one of the follow-
ing:

o d to indicate that data are geographical coordinates (in degrees).

o g to indicate that data are geographical coordinates

o l to take log10 of values before scaling.

o ppower to raise values to power before scaling.

o t  to  indicate  that  input  coordinates  are  time  relative  to
TIME_EPOCH.

o T to indicate that 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 projec-
tion 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.

-Jproj|EPSG:n
Starting  at  GMT6  it is possible to use the PROJ 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
syntax  (that  is  the syntax of the proj and cs2cs programs) so
users are referred to PROJ Applications for the details.

The usage of PROJ 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 or GDAL) we can
either  use  double  quotes  as  in  -Ja+proj=merc  +ellps=WGS84
+units=ma    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 GDALas data
sub-directory). For example -JEPSG:4326 sets the WGS-84  system.

For mapproject and grdproject we can go directly from the refer-
encing 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 grd-
project we can use all PROJ projections, the situations is, how-
ever,  rather more limited for mapping purposes.  Here, only the
subset of the PROJ projections that can be mapped into  the  GMT
projections  syntax  is available to use. Another aspect that is
not present in PROJ, because itas 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
a/1:xxxa to the end of the projection parameters.

The -R option
Syntax

-Rxmin/xmax/ymin/ymax[+r][+uunit]
Specify the region of interest. (See cookbook information).

Description

The -R option defines the map region or data domain of interest. It may
be specified in one of seven ways (options 1 and 2 are shown in  panels
a) and b) respectively of the Figure Map region):

1. -Rxmin/xmax/ymin/ymax[+uunit].  This  is the standard way to specify
Cartesian data domains and geographic regions when using map projec-
tions  where  meridians  and  parallels are rectilinear. Optionally,
append +uunit to specify a region  in  projected  units  (e.g.,  UTM
meters)  where  xmin/xmax/ymin/ymax  are Cartesian projected coordi-
nates compatible with the chosen projection and unit is an allowable
distance unit.

2. -Rxlleft/ylleft/xuright/yuright+r.  This form is useful for map pro-
jections that are  oblique,  making  meridians  and  parallels  poor
choices  for map boundaries. Here, we instead specify the lower left
corner and upper right corner geographic  coordinates,  followed  by
the  modifier +r. This form guarantees a rectangular map even though
lines of equal longitude and latitude are not straight lines.

3. -Rg or -Rd. These forms can be used to quickly  specify  the  global
domain  (0/360  for  -Rg  and  -180/+180  for -Rd in longitude, with
-90/+90 in latitude).

4. -Rgridfile. This will copy the domain settings found for the grid in
specified  file.  Note  that  depending on the nature of the calling
module, this mechanism will also set grid spacing and  possibly  the
grid   registration  (see  cookbook/options:Grid  registration:  The
**-r** option).

5. -Rcode1,code2,^<i>a|[+e|r|Rincs]]. This indirectly supplies  the  region
by  consulting  the  DCW  (Digital  Chart of the World) database and
derives the bounding regions for one or more countries given by  the
codes. Simply append one or more comma-separated countries using the
two-character ISO 3166-1 alpha-2  convention.   To  select  a  state
within  a  country  (if  available),  append  .state, e.g, US.TX for
Texas. To specify a whole continent, prepend = to any of the  conti-
nent  codes AF (Africa), AN (Antarctica), AS (Asia), EU (Europe), OC
(Oceania), NA (North America), or SA (South America). The  following
modifiers can be appended:

o +r  to  adjust  the region boundaries to be multiples of the steps
indicated by inc, xinc/yinc, or winc/einc/sinc/ninc [default is no
adjustment].  For example, -RFR+r1 will select the national bound-
ing box of France rounded to nearest integer degree.

o +R to extend the region outward by adding the amounts specified by
inc,  xinc/yinc, or winc/einc/sinc/ninc [default is no extension].

o +e to adjust the region boundaries to be multiples  of  the  steps
indicated  by inc, xinc/yinc, or winc/einc/sinc/ninc, while ensur-
ing that the bounding box extends  by  at  least  0.25  times  the

6. -Rjustifyx0/y0/nx/ny,  where justify 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). The two character code justify
indicates which point on a rectangular grid region the x0/y0 coordi-
nates  refer to and the grid dimensions nx and ny are used with grid
spacings given via -I  to  create  the  corresponding  region.  This
method can be used when creating grids. For example, -RCM25/25/50/50
specifies a 50x50 grid centered on 25,25.

7. -Rxmin/xmax/ymin/ymax/zmin/zmax. This method can be  used  for  per-
spective  views  with  the  -Jz and the -p option, where the z-range
(zmin/zmax) is appended to the first method to  indicate  the  third
dimension. This is not used for -p without -Jz, in which case a per-
spective view of the place is plotted with no third dimension
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.

The -U option
Syntax

-U[label|+c][+jjust][+odx/dy]
Draw GMT time stamp logo on plot. (See cookbook information).

Description

The -U option draws the GMT system time stamp on the plot. The  follow-
ing modifiers are supported:

o label  to  append  the text string given in label (which must be sur-
rounded by double quotes if it contains spaces).

o +c to plot the current command string.

o +jjustify to specify the justification of the time stamp, where  jus-
tify is a two-character justification code that is a combination of a
horizontal (L(eft), C(enter), or  R(ight))  and  a  vertical  (T(op),
M(iddle), or B(ottom)) code [default is BL].

o +odx[/dy]  to  offset  the  anchor point for the time stamp by dx and
optionally dy (if different than dx).

The  GMT  parameters  MAP_LOGO,  MAP_LOGO_POS,   FONT_LOGO   and   FOR-
MAT_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  environ-
ment variable TZ (generally local time).

The -V option
Syntax

-V[level]
Select verbosity level [w]. (See cookbook information).

Description

The  -V option controls the verbosity mode, which determines which mes-
sages are sent to standard error. Choose among 7 levels  of  verbosity;

o q - Quiet, not even fatal error messages are produced.

o e - Error messages only.

o w - Warnings.

o t - Timings (report runtimes for time-intensive algorithms).

o i - Informational messages (same as -V only).

o c - Compatibility warnings (if compiled with backward-compatibility).

o d - Debugging messages.

This option can also be set by specifying the  default  GMT_VERBOSE  as
quiet,  error, warning, timing, compat, information, or debug, in order
of increased verbosity [default is warning].

The -X -Y options
Syntax

-X[a|c|f|r][xshift]
Shift plot origin. (See cookbook information).

-Y[a|c|f|r][yshift]
Shift plot origin. (See cookbook information).

Description

The -X and -Y options shift the plot origin  relative  to  the  current
origin by (xshift,yshift). Optionally, append the length unit (c, i, or
p). Default  is  (MAP_ORIGIN_X,  MAP_ORIGIN_Y)  for  new  plots,  which
ensures  that boundary annotations fit on the page. Subsequent overlays
will be co-registered with the  previous  plot  unless  the  origin  is
shifted  using  these  options.  The  following modifiers are supported
[default is r]:

o Prepend a to shift the origin back to  the  original  position  after
plotting.

o Prepend  c  to center the plot on the center of the paper (optionally

o Prepend f to shift the origin relative to the fixed lower left.

o Prepend r to move the origin relative to its current location.

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  bounding  box
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.

The -a option
Syntax

-a[[col=]name][,^<i>a|]
Control how aspatial data are handled in GMT  during  input  and
output.

Description

GMT  relies  on  external  tools  to translate geospatial files such as
shapefiles into a format we can read. The  tool  ogr2ogr  in  the  GDAL
package can do such translations and preserve the aspatial metadata via
a new OGR/GMT format specification (See  the  cookbook  chapter  /cook-
book/ogrgmt-format). For this to be useful we need a mechanism to asso-
ciate certain metadata values with required input  and  output  columns
expected  by  GMT  programs.  The -a option allows you to supply 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 as data input for column col. The given aspatial field thus replaces
any  other  value  already set. Note: col = 0 is the first data column.
Note: If no aspatial attributes are needed then the -a  option  is  not
needed a GMT will still process and read such data files.

OGR/GMT input with -a option
If  you need to populate GMT data columns with (constant) values speci-
fied by aspatial attributes, use -a and append any number of comma-sep-
arated col=name associations. For example, -a2=depth will read the spa-
tial x,y columns from the file and add a third (z) column based on  the
value  of the aspatial field called depth. You can also associate aspa-
tial fields with other settings such as labels, fill colors, pens,  and
values  (for  looking-up  colors)  by letting the col value be one of D
(for distance), G (for fill), I (for ID), L (for label), T (for  text),
W  (for  pen), or Z (for value). This works analogously to how standard
multi-segment files can pass such options via its segment headers  (See
the cookbook chapter /cookbook/file-formats). Note: If the leading col=
is omitted, the column value is automatically incremented  starting  at
2.

OGR/GMT output with -a option
GMT  table-writing  tools  can also output the OGR/GMT format directly.
Specify if certain GMT data columns  with  constant  values  should  be
stored  as  aspatial  metadata  using  col=name[:type],  where  you can
optionally specify what data type it should be from the options double,
float,  integer,  char,  string, logical, byte, or datetime [default is
double]. As for input, you can also use the special col  entries  of  D
(for  distance), G (for fill), I (for ID), L (for label), T (for text),
W (for pen), or Z (for value) to have values stored as options in  seg-
ment  headers  be  used as the source for the named aspatial field. The
type will be set automatically for these special col entries.  Finally,
for  output  you  must  append +ggeometry, where geometry can be any of
[M]POINT|LINE|POLY; where M  represents  the  multi-versions  of  these
three  geometries.  Use  upper-case +G to signal that you want to split
any line or polygon features that straddle the Dateline.

The -bi option
Syntax

-bi[ncols][type][w][+l|b]
Select native binary format for primary input (secondary  inputs
are always ASCII).

Description

Select  native binary format for primary input, where ncols is the num-
ber of data columns of given type and type must be one of:

o c - int8_t (1-byte signed char)

o u - uint8_t (1-byte unsigned char)

o h - int16_t (2-byte signed int)

o H - uint16_t (2-byte unsigned int)

o i - int32_t (4-byte signed int)

o I - uint32_t (4-byte unsigned int)

o l - int64_t (8-byte signed int)

o L - uint64_t (8-byte unsigned int)

o f - 4-byte single-precision float

o d - 8-byte double-precision float

o x - use to skip ncols anywhere in the record

For records with mixed types, simply append additional  comma-separated
combinations of ncols type (no space). The following modifiers are sup-
ported:

o w after any item to force byte-swapping

o +l|b to indicate that the entire data file should be read as  lit-
tle- 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 pro-
gram. When using native binary data the user must be aware of the  fact
that  GMT has no way of determining the actual number of columns in the
file. Native binary files may have  a  header  section,  where  the  -h
option  can  be  used  to  skip the first n bytes. If the input file is
netCDF, no -b is needed; simply append ?var1/var2/^<i>a| to the filename to
specify  the variables to be read (see /cookbook/file-formats and Modi-
an  example  that writes a binary file and reads it back with the first
column 4 byte float, the second column 8 byte int, and the third column
8 byte double.

echo 1.5 2 2.5 | gmt convert -bo1f,1l,1d > lixo.bin
gmt convert lixo.bin -bi1f,1l,1d

The -bo option
Syntax

-bo[ncols][type][w][+l|b]
Select native binary output.

Description

Select  native binary output, where ncols is the number of data columns
of type, which must be one of c, u, h, H, i, I, l, L, f, or d (see  -bi
types  for descriptions).  For a mixed-type output record, append addi-
tional comma-separated combinations of ncols type (no space). The  fol-
lowing modifiers are supported:

o w after any item to force byte-swapping

o +l|b  to indicate that the entire data file should be read as lit-
tle- or big-endian, respectively.

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.

The -c option
Syntax

-c[row,col|index]
Advance to the selected subplot panel.

Description

The -c option can be used to either advance the focus  of  plotting  to
the  next  panel  in the sequence (either by row or by column as set by
subplotas -A option) or to specify directly the row,col or 1-D index of
the  desired panel, when using /subplot to assemble multiple individual
panels in a matrix layout.  The -c option is only allowed when in  sub-
plot  mode.   If  no  -c  option is given for the first subplot then we
default to row=col=index=0, i.e., the upper  left  panel.   Note:  row,
col, and index all start at 0.

The -d option
Syntax

-di|onodata
Substitute specific values with NaN.

Description

The -d option allows user-coded missing data values to be translated to
official NaN values in GMT. Within GMT, any missing values  are  repre-
sented  by  the  IEEE  NaN  value.  However, user data may occasionally
denote missing data with an unlikely value (e.g.,  -99999).  Since  GMT
cannot guess this special missing data value, you can use the -d option
to have such values replaced with NaNs. Similarly, the  -d  option  can
replace  all  NaNs  with  the chosed nodata value should the GMT output
need to conform to such a requirement.

For input only, use -dinodata to examine all input columns. If any item
equals  nodata,  the value is interpreted as a missing data item and is
substituted with the value NaN.

For output only, use -donodata to examine all output  columns.  If  any
item  equals  NaN, the NaN value is substituted with the chosen missing
data value nodata.

The -e option
Syntax

-e[~]^<i>apattern^<i>a | -e[~]/regexp/[i]
Only accept ASCII data records that contain the  specified  pat-
tern.

Description

The  -e  option  offers  a built-in pattern scanner that will only pass
records that match the given pattern or  regular  expressions,  whereas
modules  that  read  ASCII  tables  will  normally process all the data
records that are read.  The test can also be inverted to only pass data
records  that  do  not match the pattern, by using -e~. The test is not
start  with  ~  you will need to escape this character with a backslash
[Default accepts all data records]. For matching data  records  against
extended regular expressions, please enclose the expression in slashes.
Append i for case-insensitive matching. To supply a list of  such  pat-
terns, give +ffile with one pattern per line.  To give a single pattern
starting with +f, escape it with a backslash.

The -f option
Syntax

-f[i|o]colinfo
Specify the data types of input and/or output columns  (time  or
geographical data).

Description

The  -f  option specifies what kind of data each input or output column
contains when map projections are not required. Optionally, append i or
o  to  make  this  apply only to input or output, respectively [Default
applies to both]. Append a text string with information about each col-
umn  (or range of columns) separated by commas. Each string starts with
the column number (0 is the first column) followed by either x  (longi-
tude),  y (latitude), T (absolute calendar time) or t (relative time in
chosen TIME_UNIT since TIME_EPOCH). If several consecutive columns have
the same format you may specify a range of columns rather than a single
column. Column ranges must be given  in  the  format  start[:inc]:stop,
where  inc  defaults  to 1 if not specified.  For example, if our input
file has geographic coordinates  (latitude,  longitude)  with  absolute
calendar  coordinates  in  the  columns  3  and  4,  we  would  specify
fi0y,1x,3:4T. All other columns are assumed to have the default (float-
ing point) format and need not be set individually.

The  shorthand  -f[i|o]g  means  -f[i|o]0x,1y (i.e., geographic coordi-
nates). A special use of -f is to select -fp[unit], which  requires  -J
and  lets  you use projected map coordinates (e.g., UTM meters) as data
input. Such coordinates are automatically inverted to longitude,  lati-
tude  during the data import. Optionally, append a length unit (see ta-
tions input-data-formats and output-data-formats.

The -g option
Syntax

-g[a]x|y|d|X|Y|D|[col]zgap[+n|p]
Examine  the spacing between consecutive data points in order to
impose breaks in the line.

Description

The -g option is used to detect gaps based on  one  or  more  criteria.
Repeat  the option to specify multiple criteria and prepend a to subse-
quent modifiers to specify that all the criteria must be  met  [default
imposes  breaks  if any one criteria is met]. The criteria is specified
using the x|y|d|X|Y|D|[col]z modifiers. The upper-case options  specify
that  the  criteria  should be applied to the projected coordinates for
modules that map data to map coordinates.

o x|X - define a gap when there is a large enough change in the x coor-
dinates (upper case to use projected coordinates).

o y|Y - define a gap when there is a large enough change in the y coor-
dinates (upper case to use projected coordinates).

o d|D - define a gap when there is  a  large  enough  distance  between
coordinates (upper case to use projected coordinates).

o [col]z - define a gap when there is a large enough change in the data
in column col [default col is 2 (i.e., 3rd column)].

A unit u may be appended to the specified gap:

o For geographic data (x|y|d), the unit may be arc d(egree),  m(inute),
and  s(econd), or (m)e(ter), f(eet), k(ilometer), M(iles), or n(auti-
cal miles) [Default is (m)e(ter)].

o For projected data (X|Y|D), the unit may be i(nch), c(entimeter),  or
p(oint) [Default unit is set by PROJ_LENGTH_UNIT].

One  of the following modifiers can be appended to gap [default imposes
breaks based on the absolute value of the difference between  the  cur-
rent and previous value]:

o +n  -  specify that the previous value minus the current column value
must exceed gap for a break to be imposed.

o +p - specify that the current value minus  the  previous  value  must
exceed gap for a break to be imposed.

Note:  For  x|y|z  with  time  data  the  unit is instead controlled by
TIME_UNIT. Note: GMT has other mechanisms that can determine line  seg-
mentation,  including  segments  defined  by  multiple  segment  header
records (see the cookbook chapter /cookbook/file-formats)  or  segments
defined by NaN values when IO_NAN_RECORDS is set to pass [default skips
NaN values].

The -h option
Syntax

Specify that input and/or output file(s) have n  header  records
[default is 0].

Description

Specify  that  the  primary  input  file(s) has n header record(s). The
0].  Use  -hi if only the primary input data should have header records
[Default will write out header records if the input  data  have  them].
For  output  you  may control the writing of header records using -h[o]
and the optional modifiers:

o +d to remove existing header records.

o +c to add a header comment with column names to the  output  [default
is no column names].

block [default is no segment header].

o +r to add a remark comment to the output [default is no comment]. The
remark string may contain \n to indicate line-breaks.

o +t  to  add  a title comment to the output [default is no title]. The
title string may contain \n to indicate line-breaks.

Note: Blank lines and lines starting with # are always skipped. To  use
IO_HEADER_MARKER. With -h in effect the first n records are taken  ver-
batim  as headers and not skipped even if any is starting with #. Note:
If used with native binary data (using -b) we interpret  n  to  instead
mean the number of bytes to skip on input or pad on output.

The -i option
Syntax

-icols[+l][+ddivisor][+sscale][+ooffset][,^<i>a|][,t[word]]
Select  specific  data  columns  for primary input, in arbitrary
order.

Description

The -i option allows you to specify which input file physical data col-
umns  to  use  and  in what order. Specify 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  (i.e.,  column  0)].  Columns  can  be
repeated. The chosen data columns will be used as given and columns not
listed will be skipped. Optionally, append one of the  following  modi-
fiers to any column or column range to transform the input columns:

o +l to take the log10 of the input values.

o +d to divide the input values by the factor divisor [default is 1].

o +s to multiply the input values by the factor scale [default is 1].

o +o to add the given offset to the input values [default is 0].

To read from a given column until the end of the record, leave off stop
when specifying the column range. 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.

The -j option (spherical distance calculations)
Syntax

-je|f|g
Determine how spherical distances are calculated in modules that
support this [Default is -jg].

Description

GMT has different ways to compute distances on planetary bodies:

o -jg  to  perform  great circle distance calculations, with parameters
such as distance increments  or  radii  compared  against  calculated
great circle distances [Default is -jg].

o -jf  to  select  Flat  Earth mode, which gives a more approximate but
faster result.

o -je to select ellipsoidal (or geodesic) mode for the  highest  preci-
sion and slowest calculation time.

Note:  All spherical distance calculations depend on the current ellip-
soid   (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).

The -l option
Syntax

tify][+ooff][+ppen][+sscale][+wwidth]
Add a map legend entry to the session legend  information  file  for
the current plot.

Description

The  -l option is used to automatically build the specfile that is read
by the /legend module to  create  map  or  plot  legends.  This  allows
detailed  and  complicated legends that mix a variety of items, such as
symbols, free text, colorbars, scales, images, and more. Yet, a  simple
legend  will  suffice for the vast majority of plots displaying symbols
or lines. Optionally, append a text label to describe  the  entry.  The
following  modifiers are supported to allow further changes to the leg-
end that is built by /legend (upper-case modifiers reflect legend codes
described in /legend, which provides more details and customization):

o +D to draw a horizontal line in the given pen before the legend entry
is placed [default is no line].

o +G to add the vertical space specified by gap [default  is  no  extra
space].

o +L to set a line text. Optionally, prepend a horizontal justification
code L(eft), C(enter), or R(ight) for text [default is C].

o +N to change the number of columns used to set the  following  legend
items to cols [default is 1].

o +S to override the size of the current symbol for the legend or set a
height if plotting a line or contour [default uses the same symbol as
plotted].

o +V  to start and +vpen to stop drawing vertical line from previous to
current horizontal line [default is no vertical line].

o +f  to  set  the  font  used  for  the  legend  header  [default   is
FONT_TITLE].

o +g to set the fill used for the legend frame [default is white].

o +j  to set placement of the legend using the two-character justifica-
tion code justify [default is TR].

o +o to set the offset from legend frame to anchor  point  [default  is
0.2c].

o +p to set the pen used for the legend frame [default is 1p].

o +s  to  resize  all  symbol  and  length sizes in the legend by scale
[default is no scaling].

o +w to set legend frame width [default is auto].

Note: Default pen is given by MAP_DEFAULT_PEN. Note: +H,  +g,  +j,  +o,
+p,  +w,  and +s will only take effect if appended to the very first -l
option for a plot. The +N modifier, if appended to the first -l option,
affects  the legend width (unless set via +w); otherwise it just subdi-
vides the available width among the specified columns. If legend is not
called  explicitly  we  will call it implicitly when finishing the plot
via /end. Note: If auto-coloring is used for pens or fills  and  -l  is
set  then  label  may  contain a C-format for integers (e.g., %3.3d) or
just # and we will use the sequence number with the format to build the
label  entries.   Alternatively, give a list of comma-separated labels,

The -n option
Syntax

-n[b|c|l|n][+a][+bg|p|n][+c][+tthreshold]
Select grid interpolation mode.

Description

The -n  option  controls  parameters  used  for  2-D  grids  resampling
[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]. Append one of the following to select the type of
spline used:

o b to use B-spline smoothing.

o c to use bicubic interpolation.

o l to use bilinear interpolation.

o n to use nearest-neighbor value  (for  example  to  plot  categorical
data).

The following modifiers are supported:

o +a  to  switch  off  antialiasing  (where  supported)  [default  uses
antialiasing].

o +b to override boundary conditions used,  by  appending  g  for  geo-
graphic,  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.

o +c  to  clip  the interpolated grid to input z-min/z-max [default may
exceed limits].

o +t to control how close to nodes with NaNs the interpolation will  go
based  on  threshold. A threshold of 1.0 requires all (4 or 16) nodes
involved in interpolation to be non-NaN. For example, 0.5 will inter-
polate  about half way from a non-NaN value and 0.1 will go about 90%
of the way [default is 0.5].

The -o option
Syntax

-ocols[,a|][,t[word]]
Select specific data columns for primary  output,  in  arbitrary
order.

Description

The  -o  option  allows  you to specify which output file physical data
columns to use and in what order. Specify individual columns or  column
ranges  in  the format start[:inc]:stop, where inc defaults to 1 if not
specified, separated by commas [Default writes all  columns  in  order,
starting  with  the  first  column  (i.e.,  column  0)]. Columns can be
repeated. The chosen data columns will be used as given and columns not
listed  will  be skipped. To write from a given column until the end of
the record, leave off stop when specifying the column range.

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, while -ot will only output  the  trailing  text
(or  selected  word). 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.

The -p option
Syntax

-p[x|y|z]azim[/elev[/zlevel]][+wlon0/lat0[/z0]][+vx0/y0]
Select perspective view and set the azimuth and elevation of the
viewpoint.

Description

All plotting programs that normally  produce  a  flat,  two-dimensional
illustration can be told to view this flat illustration from a particu-
lar vantage point, resulting in a perspective view. You can select per-
spective  view  with the -p option by setting the azimuth (azim) of the
viewpoint [Default is 180]. The following modifiers are supported:

o x|y|z to plot against the awalla x = level (using x)  or  y  =  level
(using y) or the horizontal plain (using z) [default is z].

o /elev to set the elevation of the viewport [Default is 90].

o /zlevel  to  indicate  the z-level at which all 2D material, like the
plot frame, is plotted (only valid when -p is used  in  consort  with
-Jz or -JZ) [Default is at the bottom of the z-axis].

For  frames  used for animation, we fix the center of your data domain.
Specify another center using one of the following modifiers:

o +w to project lon0/lat0 (and z0 if applicable) to the center  of  the
page size.

o +v  to  specify  the  coordinates  of the projected 2-D view point as
x0/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 (in modern mode this
also supplies the previous -Jz or -JZ if doing a 3-D region).  Alterna-
tively, you can perform a simple rotation about the z-axis by just giv-
ing the rotation angle. Optionally, use +v or +w to select another axis
location than the plot origin.

The -q option
Syntax

-q[i|o][~]rows[+ccol][+a|f|s]
Select specific data rows to be read and/or written.

Description

The -q option is used to select specific data rows to be read (using -q
or -qi) or written (using -qo) [Default is all rows]. Specify  individ-
ual  rows  or  row  ranges  in  the  format start[:inc]:stop, where inc
defaults to 1 if not specified, separated by commas [Default reads  and
writes  all  rows in order, starting with the first row (i.e., row 0)].
To read (or write) from a given row until the end of  the  data,  leave
off  stop.  To  select  all the rows not specified by the given ranges,
prepend the selected rows with a leading ~. Append one of the following
modifiers to control how the rows are counted [Default is +a]:

o +a to count all rows in the data set.

o +f to reset the count at the start of each file.

o +s to reset the count at the start of each segment.

Alternatively,  use  +ccol  to  indicate that the arguments instead are
min/max data limits for the values in column col. With +ccol, only rows
whose  data  for  the given column col are within the range(s) given by
the min/max limits are read (with -qi) or  written  (with  -qo).  Note:
Because  arguments may contain colons or be negative, your must specify

Note: Header records do  not  increase  the  row  counters;  only  data
records do.

The -r option (grid registration)
Syntax

-r[g|p]
Select gridline or pixel node registration.

Description

All  2-D  grids  in  GMT have their nodes organized in one of two ways,
known as gridline and pixel registration. The GMT default  is  gridline
registration  (-rg);  programs that allow for the creation of grids can
use the -r option (or -rp) to select pixel registration instead.

Most observed data tend to be in gridline registration while  processed
data  sometime may be distributed in pixel registration.  While you may
convert between  the  two  registrations  this  conversion  looses  the
Nyquist frequency and dampens the other high frequencies. It is best to
avoid any registration conversion if you can help  it.  Planning  ahead
may   be   important.   (Node  registrations  are  defined  in  Section
option_nodereg of the GMT Technical Reference and Cookbook.)

The -s option
Syntax

-s[cols][+a][+r]
Suppress output of data records whose z-value(s) equal NaN.

Description

The -s option can be used to suppress output for records whose  z-value
equals  NaN  [default  outputs  all  records].   Optionally,  supply  a
comma-separated list of all columns or column ranges  to  consider  for
this NaN test [default only considers the third data column (i.e., cols
= 2)]. Column ranges must be  given  in  the  format  start[:inc]:stop,
where  inc  defaults to 1 if not specified. The following modifiers are
supported:

o +r to reverse the suppression, i.e., only output  the  records  whose
z-value equals NaN.

o +a  to  suppress  the output of the record if just one or more of the
columns equal NaN [default skips record only if values in all  speci-
fied cols equal NaN]

The -t option
Syntax

-ttransp[/transp2][+f|s]
Set transparency level(s) for an overlay.

Description

The  -t option allows you to change the transparency level for the cur-
rent overlay by appending the transp  percentage  in  the  0-100  range
[default  is  0  (i.e., opaque)]. Normally, transp applies to both fill
and stroke, but you can limit  the  transparency  to  one  of  them  by
appending  +f  or  +s  for fill or stroke, respectively. Alternatively,
append /transp2 to set separate transparencies for fills and strokes.

Transparency may also be controlled on a feature by feature basis  when
setting  color  or fill (see the cookbook section -Gfill_attrib). Note:
The modules /plot, /plot3d, and /text can all change transparency on  a
record-by-record  basis  if  -t is given without argument and the input
file supplies variable transparencies  as  the  last  numerical  column
value(s).  Note:  The  transparency  is only visible when PDF or raster
format output is selected because the PostScript language does not sup-
port  transparency.  Only  the PNG format selection adds a transparency
layer in the image (for further processing).

The -w option
Syntax

-wy|a|w|d|h|m|s|cperiod[/phase][+ccol]
Convert input records to a cyclical coordinate.

Description

The -w option converts the input x-coordinate to a cyclical coordinate,
or  a  different input column if selected via the +c modifier. Temporal
data (i.e., regular time series) can be analyzed for periods via  stan-
dard  spectral  analysis,  such  as offered by /spectrum1d and /grdfft.
However, it is often of interest to examine aspects of such  periodici-
ties  in  the  time domain.  To enable such analyses we need to convert
our monotonically increasing time coordinates  to  periodic  or  cyclic
coordinates  so that data from many cycles can be stacked, binned, dis-
played in histograms, etc. The conversion from input x, y, or z coordi-
nates to wrapped, periodic coordinates follows the simple equation

t' = (t - \tau) \;\mathrm{mod}\; T,

where  t  is  the  input  coordinate,  \tau is a phase-shift (typically
zero), and T is the desired period for the modulus  operator,  yielding
cyclic  coordinates  t'.  GMT  offers many standard time cycles in pre-
scribed units plus a custom cycle for other types of Cartesian  coordi-
nates.  The  table  below  shows the values for units, phase and period
that are prescribed and only requires the user to  specify  the  corre-
sponding wrapping code (y|a|w|d|h|m|s|cperiod):

+-----+---------------+----------+-------+-------+
|Code | Purpose       | Period   | Phase | Range |
|     | (unit)        |          |       |       |
+-----+---------------+----------+-------+-------+
|y    | Yearly  cycle | 1 year   | 0     | 0a1   |
|     | (normalized)  |          |       |       |
+-----+---------------+----------+-------+-------+
|a    | Annual  cycle | 1 year   | 0     | 0a12  |
|     | (month)       |          |       |       |
+-----+---------------+----------+-------+-------+
|w    | Weekly  cycle | 1 week   | 0     | 0a7   |
|     | (day)         |          |       |       |
+-----+---------------+----------+-------+-------+
|d    | Daily   cycle | 1 day    | 0     | 0a24  |
|     | (hour)        |          |       |       |
+-----+---------------+----------+-------+-------+
|h    | Hourly  cycle | 1 hour   | 0     | 0a60  |
|     | (minute)      |          |       |       |
+-----+---------------+----------+-------+-------+
|m    | Minute  cycle | 1 minute | 0     | 0a60  |
|     | (second)      |          |       |       |
+-----+---------------+----------+-------+-------+
|s    | Second  cycle | 1 second | 0     | 0a1   |
|     | (second)      |          |       |       |
+-----+---------------+----------+-------+-------+
|c    | Custom  cycle | T        | \tau  | 0a1   |
|     | (normalized)  |          |       |       |
+-----+---------------+----------+-------+-------+

Optionally, append +ccol to select the input column  with  the  coordi-
nates  to  be  wrapped, [default col is 0 (i.e., the first column)]. If
the custom cycle c is chosen then you must also supply the  period  and
optionally  any  phase  [default  is  0] in the same units of your data
(i.e., no units should be appended to -w).

Note: Coordinates for w in the range 0-1 correspond to the first day of
the  week  [Monday]  but can be changed via TIME_WEEK_START. Note: If a
temporal cycle is indicated then we implicitly set -f to indicate abso-
lute  time  (unless  already  set separately). See the cookbook section
Examining data cycles: The -w option for examples.

The -x option
Syntax

-x[[-]n]
Specify  the  number  of  active  cores  to  be  used   in   any

Description

The   -x  option  limits  the  number  of  cores  to  be  used  in  any
OpenMP-enabled multi-threaded algorithms [default is to use all  avail-
able  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, with the exception of /movie and /batch which handle their own
parallel execution.

The -: option
Syntax

-:[i|o]
Swap 1st and 2nd column on input and/or output.

Description The -: option swaps the 1st and 2nd  column  on  input  and
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  cook-
book/options:Input columns selection: The **-i** option. Note that com-
mand  line  arguments  that  may take geographic coordinates (e.g., -R)
always expect longitude before latitude. Also, geographical  grids  are
expected to have the longitude as first (minor) dimension.

Module help and configuration
-^ or just -
Print a short message about the syntax of the command, then exit
(NOTE: on Windows just use -).

-+ or just +
Print an extensive usage (help) message, including the  explana-
tion  of  any  module-specific  option  (but  not the GMT common
options), then exit.

-? or no arguments
Print a complete usage (help) message, including the explanation
of all options, then exit.

--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 triplet RGB (r/g/b, each in the range  0a255),  by
hue-saturation-value  HSV  (h-s-v,  with  ranges  of 0-360, 0-1,
0-1), by cyan/magenta/yellow/black CMYK (c/m/y/k,  each  in  the
range  0-1), or by a hexadecimal color code (#rrggbb, as used in
HTML). For a transparency effect, append  @transparency  in  the
0a100  percent  range [Default is 0 (opaque)] Note: Transparency
effects are only visible when PDF or a raster graphics format is
mation 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 poly-
gons.  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
[300].  For  1-bit rasters: use upper case P  for inverse video,
or append +fcolor and/or +bcolor to specify fore- and background
colors  (no color given means transparency).  See /cookbook/pre-
defined-patterns for information  on  individual  built-in  pat-
terns.

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  out-
line.  If  you want to avoid that the outline partially obscures
the text, 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 wide.
color specifies a gray shade  or  color  (see  Specifying  Color
dota, or adotdasha, or a custom combination of  dashes  a-a  and
dots  a.a.  If any of the attributes is omitted their default or
previous setting will be retained. See GMT Cookbook &  Technical



## 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  FOR-
MAT_DATE_OUT and FORMAT_CLOCK_OUT, whereas general floating point  val-
ues are formatted according to FORMAT_FLOAT_OUT. Be aware that the for-
mat 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 set-
ting.



## 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  apackinga 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][+ooff-
set][+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 pro-
vided, as in +sscale, then 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 it 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: aza. See grdconvert and Sections modi-
fiers-for-CF and grid-file-format of the GMT  Technical  Reference  and
Cookbook  for  more  information, particularly on how to read slices of
3-, 4-, or 5-dimensional grids.

When writing a netCDF file, the grid is  stored  by  default  with  the
variable  name  aza.  To  specify another variable name varname, append
?varname to the file name. 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.



## CLASSIC MODE OPTIONS

       These  options  are  only used in classic mode and are listed here just
for reference.

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  sys-
tem].  Required for all but the first plot command when building
multi-layer plots.

-P     Select aPortraita plot orientation [Default is aLandscapea;  see
gmt.conf  or gmtset to change the PS_PAGE_ORIENTATION parameter,
or  supply  --PS_PAGE_ORIENTATION=orientation  on  the   command
line].



       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 direc-
tories. 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/



       docs



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