.. index:: ! gmt.conf

********
gmt.conf
********

Configuration for GMT

Description
-----------

The following is a list of the parameters that are user-definable in
GMT. The parameter names are always given in **UPPER CASE**. The
parameter values are case-insensitive unless otherwise noted. The system
defaults are given in brackets [ for SI (or US) ].
Note that default distances and lengths below are
given in both cm or inch; the chosen default depends on your choice of
default unit (see :term:`PROJ_LENGTH_UNIT`). You can explicitly specify
the unit used for distances and lengths by appending **c** (cm), **i**
(inch), or **p** (points). When no unit is indicated the value will be
assumed to be in the unit set by :term:`PROJ_LENGTH_UNIT`. Several
parameters take only **true** or **false**. Finally, most of these
parameters can be changed on-the-fly via the **--PARAMETER**\ =\ *VALUE*
option to any GMT program. However, a few are static and are only
read via the **gmt.conf** file; these are labeled (static).

Common Specifications
---------------------

The full explanation for how to specify pens, pattern fills, colors, and
fonts can be found in the :doc:`gmt` man page.

================================= ================
THEMATIC SUB-SECTIONS             *prefix*
================================= ================
`COLOR Parameters`_               **COLOR_**
`DIR Parameters`_                 **DIR_**
`FONT Parameters`_                **FONT_**
`FORMAT Parameters`_              **FORMAT_**
`GMT Miscellaneous Parameters`_   **GMT_**
`I/O Parameters`_                 **IO_**
`MAP Parameters`_                 **MAP_**
`Projection Parameters`_          **PROJ_**
`PostScript Parameters`_          **PS_**
`Calendar/Time Parameters`_       **TIME_**
================================= ================


.. _COLOR Parameters:

COLOR Parameters
~~~~~~~~~~~~~~~~

.. glossary::

    **COLOR_BACKGROUND**
        Color used for the background of images (i.e., when z < lowest color
        table entry) [black].

    **COLOR_FOREGROUND**
        Color used for the foreground of images (i.e., when z > highest
        color table entry) [white].

    **COLOR_HSV_MAX_S**
        Maximum saturation (0-1) assigned for most positive intensity value [0.1].

    **COLOR_HSV_MIN_S**
        Minimum saturation (0-1) assigned for most negative intensity value [1.0].

    **COLOR_HSV_MAX_V**
        Maximum value (0-1) assigned for most positive intensity value [1.0].

    **COLOR_HSV_MIN_V**
        Minimum value (0-1) assigned for most negative intensity value [0.3].

    **COLOR_MODEL**
        Selects in which color space a CPT should be interpolated.
        By default, color interpolation takes place directly on the RGB
        values which can produce some unexpected hues, whereas interpolation
        directly on the HSV values better preserves those hues. The choices
        are: **none** (default: use whatever the **COLOR_MODEL** setting in the
        CPT demands), **rgb** (force interpolation in RGB),
        **hsv** (force interpolation in HSV), **cmyk** (assumes colors are
        in CMYK but interpolates in RGB).

    **COLOR_NAN**
        Color used for the non-defined areas of images (i.e., where z = NaN) [127.5].

.. _DIR Parameters:

DIR Parameters
~~~~~~~~~~~~~~

.. glossary::

    **DIR_CACHE**
        Cache directory where we save remote filenames starting in **@** (e.g., @hotspots.txt) [~/.gmt/cache].

    **DIR_DATA**
        Session data directory. Overrides the value of the environment variable **$GMT_DATADIR**
        (see :ref:`Directory parameters` in the CookBook).

    **DIR_DCW**
        Path to optional Digital Chart of the World polygon files.

    **DIR_GSHHG**
        Path to GSHHG files. Defaults to **$GMT_SHAREDIR**/coast if empty.

.. _FONT Parameters:

FONT Parameters
~~~~~~~~~~~~~~~

.. glossary::

    **FONT**
        Sets the default for all fonts, except :term:`FONT_LOGO`. This setting is
        not included in the **gmt.conf** file.

    **FONT_ANNOT**
        Sets both :term:`FONT_ANNOT_PRIMARY` and :term:`FONT_ANNOT_SECONDARY` to the value specified.
        This setting is not included in the **gmt.conf** file.

    **FONT_ANNOT_PRIMARY**
        Font used for primary annotations, etc. [12p,Helvetica,black]. When
        **+** is prepended, scale fonts, offsets and tick-lengths relative
        to :term:`FONT_ANNOT_PRIMARY`.

    **FONT_ANNOT_SECONDARY**
        Font to use for time axis secondary annotations
        [14p,Helvetica,black].

    **FONT_HEADING**
        Font to use when plotting headings above subplots [32p,Helvetica,black].

    **FONT_LABEL**
        Font to use when plotting labels below axes [16p,Helvetica,black].

    **FONT_LOGO**
        Font to use for text plotted as part of the GMT time logo
        [8p,Helvetica,black].

    **FONT_TAG**
        Font to use for subplot panel tags such as a), ii)
        [20p,Helvetica,black].

    **FONT_TITLE**
        Font to use when plotting titles over graphs [24p,Helvetica,black].

.. _FORMAT Parameters:

FORMAT Parameters
~~~~~~~~~~~~~~~~~

.. glossary::

    **FORMAT_CLOCK_IN**
        Formatting template that indicates how an input clock string is
        formatted. This template is then used to guide the reading of clock
        strings in data fields. To properly decode 12-hour clocks, append am
        or pm (or upper case) to match your data records. As examples, try
        hh:mm, hh:mm:ssAM, etc. [hh:mm:ss].

    **FORMAT_CLOCK_MAP**
        Formatting template that indicates how an output clock string is to
        be plotted. This template is then used to guide the formatting of
        clock strings in plot annotations. See :term:`FORMAT_CLOCK_OUT` for
        details. [hh:mm:ss].

    **FORMAT_CLOCK_OUT**
        Formatting template that indicates how an output clock string is to
        be formatted. This template is then used to guide the writing of
        clock strings in data fields. To use a floating point format for the
        smallest unit (e.g., seconds), append .xxx, where the number of x
        indicates the desired precision. If no floating point is indicated
        then the smallest specified unit will be rounded off to nearest
        integer. For 12-hour clocks, append am, AM, a.m., or A.M. (GMT
        will replace a\|A with p\|P for pm). If your template starts with a
        leading hyphen (-) then each integer item (y,m,d) will be printed
        without leading zeros (default uses fixed width formats). As
        examples, try hh:mm, hh.mm.ss, hh:mm:ss.xxxx, hha.m., etc.
        [hh:mm:ss]. If the format is simply - then no clock is output and
        the ISO T divider between date and clock is omitted.

    **FORMAT_DATE_IN**
        Formatting template that indicates how an input date string is
        formatted. This template is then used to guide the reading of date
        strings in data fields. You may specify either Gregorian calendar
        format or ISO week calendar format. Gregorian calendar: Use any
        combination of yyyy (or yy for 2-digit years; if so see
        :term:`TIME_Y2K_OFFSET_YEAR`), mm (or o for abbreviated month name in
        the current time language), and dd, with or without delimiters. For
        day-of-year data, use jjj instead of mm and/or dd. Examples can be
        ddmmyyyy, yy-mm-dd, dd-o-yyyy, yyyy/dd/mm, yyyy-jjj, etc. ISO
        Calendar: Expected template is yyyy[-]W[-]ww[-]d, where ww is ISO
        week and d is ISO week day. Either template must be consistent,
        e.g., you cannot specify months if you do not specify years.
        Examples are yyyyWwwd, yyyy-Www, etc. [yyyy-mm-dd].

    **FORMAT_DATE_MAP**
        Formatting template that indicates how an output date string is to
        be plotted. This template is then used to guide the plotting of date
        strings in data fields. See :term:`FORMAT_DATE_OUT` for details. In
        addition, you may use a single o instead of mm (to plot month name)
        and u instead of W[-]ww to plot "Week ##". Both of these text
        strings will be affected by the :term:`GMT_LANGUAGE`,
        :term:`FORMAT_TIME_PRIMARY_MAP` and :term:`FORMAT_TIME_SECONDARY_MAP`
        setting. [yyyy-mm-dd].

    **FORMAT_DATE_OUT**
        Formatting template that indicates how an output date string is to
        be formatted. This template is then used to guide the writing of
        date strings in data fields. You may specify either Gregorian
        calendar format or ISO week calendar format. Gregorian calendar: Use
        any combination of yyyy (or yy for 2-digit years; if so see
        :term:`TIME_Y2K_OFFSET_YEAR`), mm (or o for abbreviated month name in
        the current time language), and dd, with or without delimiters. For
        day-of-year data, use jjj instead of mm and/or dd. As examples, try
        yy/mm/dd, yyyy=jjj, dd-o-yyyy, dd-mm-yy, yy-mm, etc. ISO Calendar:
        Expected template is yyyy[-]W[-]ww[-]d, where ww is ISO week and d
        is ISO week day. Either template must be consistent, e.g., you
        cannot specify months if you do not specify years. As examples, try
        yyyyWww, yy-W-ww-d, etc. If your template starts with a leading
        hyphen (-) then each integer item (y,m,d) will be printed without
        leading zeros (default uses fixed width formats) [yyyy-mm-dd]. If
        the format is simply - then no date is output and the ISO T divider
        between date and clock is omitted.

    **FORMAT_GEO_MAP**
        Formatting template that indicates how an output geographical
        coordinate is to be plotted. This template is then used to guide the
        plotting of geographical coordinates in data fields. See
        :term:`FORMAT_GEO_OUT` for details. In addition, you can append A
        which plots the absolute value of the coordinate. The default is
        ddd:mm:ss. Not all items may be plotted as this depends on the
        annotation interval.

    **FORMAT_GEO_OUT**
        Formatting template that indicates how an output geographical
        coordinate is to be formatted. This template is then used to guide
        the writing of geographical coordinates in data fields. The template
        is in general of the form [±]D or [±]ddd[:mm[:ss]][.xxx][F].
        By default, longitudes will be reported in the range [-180,180]. The
        various terms have the following purpose:

        - **D**: Use :term:`FORMAT_FLOAT_OUT` for floating point degrees [default].
        - **+D**: Output longitude in the range [0,360]
        - **-D**: Output longitude in the range [-360,0]
        - **ddd**: Fixed format integer degrees
        - **:**: delimiter used
        - **mm**: Fixed format integer arc minutes
        - **ss**: Fixed format integer arc seconds
        - **.xxx**: Floating fraction of previous integer field, fixed width.
        - **F**: Encode sign using WESN suffix
        - **G**: Same as **F** but with a leading space before suffix

    **FORMAT_FLOAT_MAP**
        Format (C language printf syntax) to be used when plotting double
        precision floating point numbers along plot frames and contours.
        For geographic coordinates, see :term:`FORMAT_GEO_MAP`. [%.12lg].

    **FORMAT_FLOAT_OUT**
        Format (C language printf syntax) to be used when printing double
        precision floating point numbers to output files. For geographic
        coordinates, see :term:`FORMAT_GEO_OUT`. [%.12lg]. To give some
        columns a separate format, supply one or more comma-separated
        *cols*:*format* specifications, where *cols* can be specific columns
        (e.g., 5 for 6th since 0 is the first) or a range of columns (e.g.,
        3-7). The last specification without column information will
        override the format for all other columns.  Alternatively, you can
        list N space-separated formats and these apply to the first N
        columns.

    **FORMAT_TIME_MAP**
        Sets both :term:`FORMAT_TIME_PRIMARY_MAP` and :term:`FORMAT_TIME_SECONDARY_MAP` to the value specified.
        This setting is not included in the **gmt.conf** file.

    **FORMAT_TIME_PRIMARY_MAP**
        Controls how primary month-, week-, and weekday-names are formatted.
        Choose among **full**, **abbreviated**, and **character**. If the
        leading **f**, **a**, or **c** are replaced with **F**, **A**, and
        **C** the entire annotation will be in upper case [full].

    **FORMAT_TIME_SECONDARY_MAP**
        Controls how secondary month-, week-, and weekday-names are
        formatted. Choose among **full**, **abbreviated**, and
        **character**. If the leading **f**, **a**, or **c** are replaced
        with **F**, **A**, and **C** the entire annotation will be in upper case [full].

    **FORMAT_TIME_STAMP**
        Defines the format of the time information in the UNIX time stamp.
        This format is parsed by the C function **strftime**, so that
        virtually any text can be used (even not containing any time
        information) [%Y %b %d %H:%M:%S].

.. _GMT Miscellaneous Parameters:

GMT Miscellaneous Parameters
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. glossary::

    **GMT_AUTO_DOWNLOAD**
        Determines if GMT is allowed to automatically download datasets and
        files from the remote server selected via :term:`GMT_DATA_SERVER`.  Default
        is *on* but you can turn this off by setting it to *off*.

    **GMT_COMPATIBILITY**
        Determines if the current GMT version should be able to parse command-line
        options for a prior major release.  Specify the major release version number,
        e.g., 4-6. If 4 is set we will parse obsolete GMT 4 options and issue warnings; if 5
        is set then parsing GMT 4 only syntax will result in errors [4]; likewise
        for 6: obsolete syntax from early GMT 5 will be considered errors.

    **GMT_DATA_SERVER**
        Address of the data directory on the remote server [The SOEST server].

    **GMT_DATA_SERVER_LIMIT**
        Upper limit on the size of remote file to download [unlimited].  Give
        the maximum file size in bytes, or append k, m, or g for kilo-, mega-,
        or giga-bytes.

    **GMT_EXPORT_TYPE**
        This setting is only used by external interfaces and controls the
        data type used for table entries.  Choose from double,
        single, [u]long, [u]int, [u]short, and [u]char [Default is double].

    **GMT_EXTRAPOLATE_VAL**
        Determines what to do if extrapolating beyond the data domain.
        Choose among 'NaN', 'extrap' or 'extrapval,val' (without quotes). In
        the first case return NaN for any element of x that is outside range
        [Default]. Second case lets the selected algorithm compute the
        extrapolation values. Third case sets the extrapolation values to
        the constant value passed in 'val' (this value must off course be
        numeric).

    **GMT_CUSTOM_LIBS**
        Comma-separated list of GMT-compliant shared libraries that extend
        the capability of GMT with additional custom modules [none]. Alternatively,
        provide a directory name, that MUST end with a slash (or back slash),
        to use all shared libraries in that directory. On Windows, if the dir
        name is made up only of a single slash ('/') search inside a subdirectory
        called 'gmt_plugins' of the directory that contains the 'gmt' executable.
        See the API documentation for how to build your own shared modules.

    **GMT_FFT**
        Determines which Fast Fourier Transform (FFT) should be used among
        those that have been configured during installation. Choose from
        **auto** (pick the most suitable for the task among available
        algorithms), **fftw**\ [,\ *planner_flag*] (The Fastest Fourier
        Transform in the West), **accelerate** (Use the Accelerate Framework
        under OS X; Note, that the number of samples to be processed must be
        a base 2 exponent), **kiss**, (Kiss FFT), **brenner** Brenner Legacy
        FFT [auto].
        FFTW can "learn" how to optimally compute Fourier transforms on the
        current hardware and OS by computing several FFTs and measuring
        their execution time. This so gained "Wisdom" will be stored in and
        reloaded from the file fftw_wisdom_<hostname> in **$GMT_USERDIR** or, if
        **$GMT_USERDIR** is not writable, in the current directory. To use this
        feature append *planner_flag*, which can be one of *measure*,
        *patient*, and *exhaustive*; see FFTW reference for details. The
        default FFTW planner flag is *estimate*, i.e., pick a (probably
        sub-optimal) plan quickly. **Note**: If you need a single transform of a
        given size only, the one-time cost of the smart planner becomes
        significant. In that case, stick to the default planner, *estimate*,
        based on heuristics.

    **GMT_GRAPHICS_FORMAT**
        Default graphics format in modern mode [pdf].

    **GMT_HISTORY**
        Passes the history of past common command options via the
        gmt.history file. The different values for this setting are:
        **true**, **readonly**, **false**, to either read and write to the
        gmt.history file, only read, or not use the file at all [true].

    **GMT_INTERPOLANT**
        Determines if linear (linear), Akima's spline (akima), natural cubic
        spline (cubic) or no interpolation (none) should be used for 1-D
        interpolations in various programs [akima].

    **GMT_LANGUAGE**
        Language to use when plotting calendar and map items such as months and
        days, map annotations and cardinal points. Select from:

        .. hlist::
           :columns: 3

           - *CN1*: Simplified Chinese
           - *CN2*: Traditional Chinese
           - *DE*: German
           - *DK*: Danish
           - *EH*: Basque
           - *ES*: Spanish
           - *FI*: Finnish
           - *FR*: French
           - *GR*: Greek
           - *HI*: Hawaiian
           - *HU*: Hungarian
           - *IE*: Irish
           - *IL*: Hebrew
           - *IS*: Icelandic
           - *IT*: Italian
           - *JP*: Japanese
           - *KR*: Korean
           - *NL*: Dutch
           - *NO*: Norwegian
           - *PL*: Polish
           - *PT*: Portuguese
           - *RU*: Russian
           - *SE*: Swedish
           - *SG*: Scottish Gaelic
           - *TO*: Tongan
           - *TR*: Turkish
           - *UK*: British English
           - *US*: US English

        If your language is not supported, please examine the
        **$GMT_SHAREDIR**/localization/gmt_us.locale file and make a similar file. Please
        submit it to the GMT Developers for official inclusion. Custom
        language files can be placed in directories **$GMT_SHAREDIR**/localization
        or ~/.gmt. **Note**: Some of these languages may require you to also
        change the :term:`PS_CHAR_ENCODING` setting.

    **GMT_MAX_CORES**
        Sets the upper limit on the number of cores any multi-threaded module might
        use (whether **-x** is selected or not) [0, i.e., as many as are available].

    **GMT_TRIANGULATE**
        Determines if we use the **Watson** [Default] or **Shewchuk**
        algorithm (if configured during installation) for triangulation.
        Note that Shewchuk is required for operations involving Voronoi
        constructions.

    **GMT_VERBOSE**
        (**-V**) Determines the level of verbosity used by GMT
        programs. Choose among 7 levels; each level adds to the verbosity of
        the lower levels: **q**\ uiet, **e**\ rrors, **w**\ arnings,
        **t**\ imings (for slow algorithms only), **i**\ nformation,
        **c**\ ompatibility warnings, and **d**\ ebugging messages [**w**].

.. _I/O Parameters:

I/O Parameters
~~~~~~~~~~~~~~

.. glossary::

    **IO_COL_SEPARATOR**
        This setting determines what character will separate ASCII output
        data columns written by GMT. Choose from tab, space, comma, and
        none [tab].

    **IO_FIRST_HEADER**
        This setting determines if the first segment header is written when
        there is only a single segment (for multiple segment it must be written).
        By default, such single-segment headers are only written if the header
        has contents. Choose from always, never, or maybe [maybe].

    **IO_GRIDFILE_FORMAT**
        Default file format for grids, with optional scale, offset and
        invalid value, written as *ff*\ [**+s**\ *scale*][**+o**\ *offset*][**+n**\ *invalid*]. The
        2-letter format indicator can be one of [**abcegnrs**][**bsifd**]. See
        :doc:`grdconvert` and Section :ref:`grid-file-format` of the
        GMT Technical Reference and Cookbook for more information.
        You may the scale as *a* for auto-adjusting the scale and/or offset of
        packed integer grids (=\ *ID*\ **+s**\ *a* is a shorthand for
        =\ *ID*\ **+s**\ *a*\ **+o**\ *a*).  When *invalid* is omitted
        the appropriate value for the given format is used (NaN or largest negative). [nf].

    **IO_GRIDFILE_SHORTHAND**
        If true, all grid file names are examined to see if they use the
        file extension shorthand discussed in Section :ref:`grid-file-format` of the GMT
        Technical Reference and Cookbook. If false, no filename expansion is done [false].

    **IO_HEADER**
        (**-h**) Specifies whether input/output ASCII files have header record(s) or not [false].

    **IO_HEADER_MARKER**
        Give a string from which any character will indicate a header record in
        an incoming ASCII data table if found in the first position [#%!;"']. If another marker
        should be used for output than the first character in the list, then append a single
        character for the output header record marker. The two sets must be separated by a comma.
        **Note**: A maximum of 7 input markers can be specified.

    **IO_LONLAT_TOGGLE**
        (**-:**) Set if the first two columns of input and output files
        contain (latitude,longitude) or (y,x) rather than the expected
        (longitude,latitude) or (x,y). false means we have (x,y) both on
        input and output. true means both input and output should be (y,x).
        IN means only input has (y,x), while OUT means only output should be (y,x). [false].

    **IO_N_HEADER_RECS**
        Specifies how many header records to expect if **-h** is used [0].
        **Note**: This will skip the specified number of records regardless of
        what they are.  Since any records starting with # is automatically
        considered a header you will only specify a non-zero number in order
        to skip headers that do not conform to that convention.

    **IO_NAN_RECORDS**
        Determines what happens when input records containing NaNs for *x*
        or *y* (and in some cases *z*) are read. This may happen, for instance,
        when there is text or other junk present instead of data coordinates, and
        the conversion to a data value fails and yields a NaN.  Choose between **skip**,
        which will report how many bad records were skipped, and **pass** [Default],
        which will quietly pass these records on to the calling
        programs. For most programs this will result in output records with
        NaNs as well, but some will interpret these NaN records to indicate
        gaps in a series; programs may then use that information to detect
        segmentation (if applicable).

    **IO_NC4_CHUNK_SIZE**
        Sets the default chunk size for the vertical (**lat**, **y**) and
        horizontal (**lon**, **x**) dimensions of
        the **z** variable. Very large chunk sizes and sizes smaller than
        128 should be avoided because they can lead to unexpectedly bad
        performance. Note that a chunk of a single precision floating point
        variable of size 2896x2896 completely fills the chunk cache of
        32 MiB. Specify the chunk size for each dimension separated by a
        comma, or **a**\ uto for optimally chosen chunk sizes in the range
        [128,256). Setting :term:`IO_NC4_CHUNK_SIZE` will produce netCDF version 4
        files, which can only be read with the netCDF 4 library, unless all
        dimensions are less than 128 or **c**\ lassic is specified for
        classic netCDF. [auto]

    **IO_NC4_DEFLATION_LEVEL**
        Sets the compression level for netCDF4 files upon output. Values
        allowed are integers from 0 (no compression) to 9 (maximum
        compression). Enabling a low compression level can dramatically
        improve performance and reduce the size of certain data. While
        higher compression levels further reduce the data size, they do so
        at the cost of extra processing time. This parameter does not
        apply to classic netCDF files. [3]

    **IO_SEGMENT_BINARY**
        Determines how binary data records with all values set to NaN are
        interpreted.  Such records are considered to be encoded segment
        headers in binary files provided the number of columns equals or
        exceeds the current setting of IO_SEGMENT_BINARY [2].  Specify 0
        or "off" to deactivate the segment header determination.

    **IO_SEGMENT_MARKER**
        This holds the character we expect to indicate a segment header in
        an incoming ASCII data or text table [>]. If this marker should be
        different for output then append another character for the output
        segment marker. The two characters must be separated by a comma. Two
        marker characters have special meaning: B means "blank line" and
        will treat blank lines as initiating a new segment, whereas N means
        "NaN record" and will treat records with all NaNs as initiating a
        new segment. If you choose B or N for the output marker then the
        normal GMT segment header is replaced by a blank or NaN record,
        respectively, and no segment header information is written. To use B
        or N as regular segment markers you must escape them with a leading
        backslash.

.. _MAP Parameters:

MAP Parameters
~~~~~~~~~~~~~~

.. glossary::

    **MAP_ANNOT_MIN_ANGLE**
        If the angle between the map boundary and the annotation baseline is
        less than this minimum value (in degrees), the annotation is not
        plotted (this may occur for certain oblique projections.) Give a
        value in the range [0,90]. [20]

    **MAP_ANNOT_MIN_SPACING**
        If an annotation would be plotted less than this minimum distance
        from its closest neighbor, the annotation is not plotted (this may
        occur for certain oblique projections.) [0p]

    **MAP_ANNOT_OBLIQUE**
        This argument is a comma-separated list of up to seven keywords:
        **separate** means longitudes will be annotated on the lower and upper
        boundaries only, and latitudes will be annotated on the left and right
        boundaries only;
        **anywhere** means annotations will occur wherever an imaginary gridline
        crosses the map boundaries; **lon_horizontal** means longitude annotations
        will be plotted horizontally; **lat_horizontal** means latitude annotations
        will be plotted horizontally; **tick_extend** means tick-marks are extended
        so the distance from the tip of the oblique tick to the map frame equals
        the specified tick length; **tick_normal** means tick-marks will be drawn
        normal to the border regardless of gridline angle; **lat_parallel** means
        latitude annotations will be plotted parallel to the border. [anywhere].

    **MAP_ANNOT_OFFSET**
        Sets both :term:`MAP_ANNOT_OFFSET_PRIMARY` and :term:`MAP_ANNOT_OFFSET_SECONDARY` to the value specified.
        This setting is not included in the **gmt.conf** file.

    **MAP_ANNOT_OFFSET_PRIMARY**
        Distance from end of tick-mark to start of annotation [5p].

    **MAP_ANNOT_OFFSET_SECONDARY**
        Distance from base of primary annotation to the top of the secondary
        annotation [5p] (Only applies to time axes with both primary and
        secondary annotations).

    **MAP_ANNOT_ORTHO**
        Determines which axes will get their annotations (for Cartesian
        projections) plotted orthogonally to the axes. Combine any **w**,
        **e**, **s**, **n**, **z** (uppercase allowed as well). [we] (if nothing specified).
        Note that this setting can be overridden via the **+a** modifier in **-B**.

    **MAP_DEFAULT_PEN**
        Sets the default of all pens related to **-W** options. Prepend
        **+** to overrule the color of the parameters
        :term:`MAP_GRID_PEN_PRIMARY`, :term:`MAP_GRID_PEN_SECONDARY`,
        :term:`MAP_FRAME_PEN`, :term:`MAP_TICK_PEN_PRIMARY`, and
        :term:`MAP_TICK_PEN_SECONDARY` by the color of :term:`MAP_DEFAULT_PEN`
        [default,black].

    **MAP_DEGREE_SYMBOL**
        Determines what symbol is used to plot the degree symbol on
        geographic map annotations. Choose between ring, degree, colon, or
        none [ring].

    **MAP_FRAME_AXES**
        Sets which axes to draw and annotate. Combine any uppercase **W**,
        **E**, **S**, **N**, **Z** to draw and annotate west, east, south,
        north and/or vertical (perspective view only) axis. Use lower case
        to draw the axis only, but not annotate. Add an optional **+** to
        draw a cube of axes in perspective view. [WESN].

    **MAP_FRAME_PEN**
        Pen attributes used to draw plain map frame [thicker,black].

    **MAP_FRAME_TYPE**
        Choose between **inside**, **plain** and **fancy** (thick boundary,
        alternating black/white frame; append **+** for rounded corners)
        [fancy]. For some map projections (e.g., Oblique Mercator), plain is
        the only option even if fancy is set as default. In general, fancy
        only applies to situations where the projected x and y directions
        parallel the longitude and latitude directions (e.g., rectangular
        projections, polar projections). For situations where all boundary
        ticks and annotations must be inside the maps (e.g., for preparing
        geotiffs), chose **inside**.  Finally, for Cartesian plots you can
        also choose **graph**\ , which adds a vector to the end of each axis.
        This works best when you reduce the number of axes plotted to one
        per dimension.  By default, the vector tip extends the length of each
        axis by 7.5%. Alternatively, append ,\ *length*, where the optional *unit*
        may be % (then *length* is the alternate extension in percent) or one
        of **c**, **i**, or **p** (then *length* is the absolute extension
        of the axis to the start of the vector base instead).  The vector stem
        is set to match :term:`MAP_FRAME_WIDTH`, while the vector
        head length and width are 10 and 5 times this width, respectively.  You
        may control its shape via :term:`MAP_VECTOR_SHAPE`.

    **MAP_FRAME_WIDTH**
        Width (> 0) of map borders for fancy map frame [5p]. **Note**: For fancy
        frames, :term:`MAP_FRAME_PEN` is automatically set to 0.1 times the
        :term:`MAP_FRAME_WIDTH` setting.

    **MAP_GRID_CROSS_SIZE**
        Sets both :term:`MAP_GRID_CROSS_SIZE_PRIMARY` and :term:`MAP_GRID_CROSS_SIZE_SECONDARY` to the value specified.
        This setting is not included in the **gmt.conf** file.

    **MAP_GRID_CROSS_SIZE_PRIMARY**
        Size of grid cross at lon-lat intersections. 0 means draw
        continuous gridlines instead.  A nonzero size will draw a symmetric grid
        cross. Signed sizes have special meaning and imply grid line ticks that
        embellish an already drawn set of gridlines: A negative size will only
        draw ticks away from Equator and Greenwich, while a positive size will
        draw symmetric ticks [0p].

    **MAP_GRID_CROSS_SIZE_SECONDARY**
        Size of grid cross at secondary lon-lat intersections. 0 means draw
        continuous gridlines instead.  A nonzero size will draw a symmetric grid
        cross.  Signed sizes have special meaning and imply grid line ticks that
        embellish an already drawn set of gridlines: A negative size will only
        draw ticks away from Equator and Greenwich, while a positive size will
        draw symmetric ticks [0p].

    **MAP_GRID_PEN**
        Sets both :term:`MAP_GRID_PEN_PRIMARY` and :term:`MAP_GRID_PEN_SECONDARY` to
        the value specified. This setting is not include in the **gmt.conf** file.

    **MAP_GRID_PEN_PRIMARY**
        Pen attributes used to draw primary grid lines in dpi units or
        points (append p) [default,black].

    **MAP_GRID_PEN_SECONDARY**
        Pen attributes used to draw secondary grid lines in dpi units or
        points (append p) [thinner,black].

    **MAP_HEADING_OFFSET**
        Distance from top of subplot panel titles to the base of the heading [18p].

    **MAP_LABEL_OFFSET**
        Distance from base of axis annotations to the top of the axis label [8p].

    **MAP_LINE_STEP**
        Determines the maximum length (> 0) of individual straight
        line-segments when drawing arcuate lines [0.75p]

    **MAP_LOGO**
        (**-U**) Specifies if a GMT logo with system timestamp should be
        plotted at the lower left corner of the plot [false].

    **MAP_LOGO_POS**
        (**-U**) Sets the justification and the position of the
        logo/timestamp box relative to the current plot's lower left corner
        (i.e., map origin) [BL/-54p/-54p].

    **MAP_ORIGIN_X**
        (**-X**) Sets the x-coordinate of the origin on the paper for a
        new plot [72p]. For an overlay, the default offset is 0.

    **MAP_ORIGIN_Y**
        (**-Y**) Sets the y-coordinate of the origin on the paper for a
        new plot [72p]. For an overlay, the default offset is 0.

    **MAP_POLAR_CAP**
        Controls the appearance of gridlines near the poles for all
        azimuthal projections and a few others in which the geographic poles
        are plotted as points (Lambert Conic, Oblique Mercator, Hammer, Mollweide,
        Sinusoidal and van der Grinten). Specify either none (in which case there
        is no special handling) or *pc_lat*/*pc_dlon*. In that case, normal
        gridlines are only drawn between the latitudes
        -*pc_lat*/+\ *pc_lat*, and above those latitudes the gridlines are
        spaced at the (presumably coarser) *pc_dlon* interval; the two
        domains are separated by a small circle drawn at the *pc_lat*
        latitude [85/90]. Note for r-theta (polar) projection where r = 0 is
        at the center of the plot the meaning of the cap is reversed, i.e.,
        the default 85/90 will draw a r = 5 radius circle at the center of
        the map with less frequent radial lines there.

    **MAP_SCALE_HEIGHT**
        Sets the height (> 0) on the map of the map scale bars drawn by
        various programs [5p].

    **MAP_TICK_LENGTH**
        Sets both :term:`MAP_TICK_LENGTH_PRIMARY` and :term:`MAP_TICK_LENGTH_SECONDARY` to the value specified.
        This setting is not included in the **gmt.conf** file.

    **MAP_TICK_LENGTH_PRIMARY**
        The length of a primary major/minor tick-marks [5p/2.5p]. If only
        the first value is set, the second is assumed to be 50% of the first.

    **MAP_TICK_LENGTH_SECONDARY**
        The length of a secondary major/minor tick-marks [15p/3.75p]. If
        only the first value is set, the second is assumed to be 25% of the first.

    **MAP_TICK_PEN**
        Sets both :term:`MAP_TICK_PEN_PRIMARY` and :term:`MAP_TICK_PEN_SECONDARY` to the value specified.
        This setting is not included in the **gmt.conf** file.

    **MAP_TICK_PEN_PRIMARY**
        Pen attributes to be used for primary tick-marks in dpi units or
        points (append p) [thinner,black].

    **MAP_TICK_PEN_SECONDARY**
        Pen attributes to be used for secondary tick-marks in dpi units or
        points (append p) [thinner,black].

    **MAP_TITLE_OFFSET**
        Distance from top of axis annotations (or axis label, if present) to
        base of plot title [14p].

    **MAP_VECTOR_SHAPE**
        Determines the shape of the head of a vector. Normally (i.e., for
        vector_shape = 0), the head will be triangular, but can be changed
        to an arrow (1) or an open V (2).
        Intermediate settings give something in between. Negative values (up
        to -2) are allowed as well [0].

.. _Projection Parameters:

Projection Parameters
~~~~~~~~~~~~~~~~~~~~~

.. glossary::

    **PROJ_AUX_LATITUDE**
        Only applies when geodesics are approximated by great circle
        distances on an equivalent sphere. Select from authalic, geocentric,
        conformal, meridional, parametric, or none [authalic]. When not none
        we convert any latitude used in the great circle calculation to the
        chosen auxiliary latitude before doing the distance calculation. See
        also :term:`PROJ_MEAN_RADIUS`.

    **PROJ_ELLIPSOID**
        The (case sensitive) name of the ellipsoid used for the map projections [WGS-84]. Choose among:

        - *Airy*: Applies to Great Britain (1830)
        - *Airy-Ireland*: Applies to Ireland in 1965 (1830)
        - *Andrae*: Applies to Denmark and Iceland (1876)
        - *APL4.9*: Appl. Physics (1965)
        - *ATS77*: Average Terrestrial System, Canada Maritime provinces (1977)
        - *Australian*: Applies to Australia (1965)
        - *Bessel*: Applies to Central Europe, Chile, Indonesia (1841)
        - *Bessel-Namibia*: Same as Bessel-Schwazeck (1841)
        - *Bessel-NGO1948*: Modified Bessel for NGO 1948 (1841)
        - *Bessel-Schwazeck*: Applies to Namibia (1841)
        - *Clarke-1858*: Clarke's early ellipsoid (1858)
        - *Clarke-1866*: Applies to North America, the Philippines (1866)
        - *Clarke-1866-Michigan*: Modified Clarke-1866 for Michigan (1866)
        - *Clarke-1880*: Applies to most of Africa, France (1880)
        - *Clarke-1880-Arc1950*: Modified Clarke-1880 for Arc 1950 (1880)
        - *Clarke-1880-IGN*: Modified Clarke-1880 for IGN (1880)
        - *Clarke-1880-Jamaica*: Modified Clarke-1880 for Jamaica (1880)
        - *Clarke-1880-Merchich*: Modified Clarke-1880 for Merchich (1880)
        - *Clarke-1880-Palestine*: Modified Clarke-1880 for Palestine (1880)
        - *CPM*: Comm. des Poids et Mesures, France (1799)
        - *Delambre*: Applies to Belgium (1810)
        - *Engelis*: Goddard Earth Models (1985)
        - *Everest-1830*: India, Burma, Pakistan, Afghanistan, Thailand (1830)
        - *Everest-1830-Kalianpur*: Modified Everest for Kalianpur (1956) (1830)
        - *Everest-1830-Kertau*: Modified Everest for Kertau, Malaysia & Singapore (1830)
        - *Everest-1830-Pakistan*: Modified Everest for Pakistan (1830)
        - *Everest-1830-Timbalai*: Modified Everest for Timbalai, Sabah Sarawak (1830)
        - *Fischer-1960*: Used by NASA for Mercury program (1960)
        - *Fischer-1960-SouthAsia*: Same as Modified-Fischer-1960 (1960)
        - *Fischer-1968*: Used by NASA for Mercury program (1968)
        - *FlatEarth*: As Sphere, but implies fast "Flat Earth" distance calculations (1984)
        - *GRS-67*: International Geodetic Reference System (1967)
        - *GRS-80*: International Geodetic Reference System (1980)
        - *Hayford-1909*: Same as the International 1924 (1909)
        - *Helmert-1906*: Applies to Egypt (1906)
        - *Hough*: Applies to the Marshall Islands (1960)
        - *Hughes-1980*: Hughes Aircraft Company for DMSP SSM/I grid products (1980)
        - *IAG-75*: International Association of Geodesy (1975)
        - *Indonesian*: Applies to Indonesia (1974)
        - *International-1924*: Worldwide use (1924)
        - *International-1967*: Worldwide use (1967)
        - *Kaula*: From satellite tracking (1961)
        - *Krassovsky*: Used in the (now former) Soviet Union (1940)
        - *Lerch*: For geoid modeling (1979)
        - *Maupertius*: Really old ellipsoid used in France (1738)
        - *Mercury-1960*: Same as Fischer-1960 (1960)
        - *MERIT-83*: United States Naval Observatory (1983)
        - *Modified-Airy*: Same as Airy-Ireland (1830)
        - *Modified-Fischer-1960*: Applies to Singapore (1960)
        - *Modified-Mercury-1968*: Same as Fischer-1968 (1968)
        - *NWL-10D*: Naval Weapons Lab (Same as WGS-72) (1972)
        - *NWL-9D*: Naval Weapons Lab (Same as WGS-66) (1966)
        - *OSU86F*: Ohio State University (1986)
        - *OSU91A*: Ohio State University (1991)
        - *Plessis*: Old ellipsoid used in France (1817)
        - *SGS-85*: Soviet Geodetic System (1985)
        - *South-American*: Applies to South America (1969)
        - *Sphere*: The mean radius in WGS-84 (for spherical/plate tectonics applications) (1984)
        - *Struve*: Friedrich Georg Wilhelm Struve (1860)
        - *TOPEX*: Used commonly for altimetry (1990)
        - *Walbeck*: First least squares solution by Finnish astronomer (1819)
        - *War-Office*: Developed by G. T. McCaw (1926)
        - *WGS-60*: World Geodetic System (1960)
        - *WGS-66*: World Geodetic System (1966)
        - *WGS-72*: World Geodetic System (1972)
        - *WGS-84*: World Geodetic System [Default] (1984)
        - *Web-Mercator*: Spherical Mercator with WGS-84 radius (1984)
        - *Moon*: Moon (IAU2000) (2000)
        - *Mercury*: Mercury (IAU2000) (2000)
        - *Venus*: Venus (IAU2000) (2000)
        - *Mars*: Mars (IAU2000) (2000)
        - *Jupiter*: Jupiter (IAU2000) (2000)
        - *Saturn*: Saturn (IAU2000) (2000)
        - *Uranus*: Uranus (IAU2000) (2000)
        - *Neptune*: Neptune (IAU2000) (2000)
        - *Pluto*: Pluto (IAU2000) (2000)

        Note that for some global projections, GMT may use a spherical
        approximation of the ellipsoid chosen, setting the flattening to
        zero, and using a mean radius. A warning will be given when this
        happens. If a different ellipsoid name than those mentioned here is
        given, GMT will attempt to parse the name to extract the
        semi-major axis (*a* in m) and the flattening. Formats allowed are:

        *a* implies a zero flattening

        *a*,\ *inv_f* where *inv_f* is the inverse flattening

        *a*,\ **b=**\ *b* where *b* is the semi-minor axis (in m)

        *a*,\ **f=**\ *f* where *f* is the flattening

        This way a custom ellipsoid (e.g., those used for other planets) may
        be used. Further note that coordinate transformations in
        **mapproject** can also specify specific datums; see the
        :doc:`mapproject` man page for further details and how to view
        ellipsoid and datum parameters.

    **PROJ_GEODESIC**
        Selects the algorithm to use for geodesic calculations. Choose between
        **Vincenty** [Default], **Rudoe**, or **Andoyer**. The **Andoyer**
        algorithm is only approximate (to within a few tens of meters) but is
        up to 5 times faster.  The **Rudoe** is given for legacy purposes.
        The default **Vincenty** is accurate to about 0.5 mm.

    **PROJ_LENGTH_UNIT**
        Sets the unit length. Choose between **c**\ m, **i**\ nch, or
        **p**\ oint [c (or i)]. Note that, in GMT, one point is defined
        as 1/72 inch (the PostScript definition), while it is often
        defined as 1/72.27 inch in the typesetting industry. There is no
        universal definition.

    **PROJ_MEAN_RADIUS**
        Applies when geodesics are approximated by great circle distances on
        an equivalent sphere or when surface areas are computed. Select from
        mean (R_1), authalic (R_2), volumetric (R_3), meridional, or
        quadratic [authalic].

    **PROJ_SCALE_FACTOR**
        Changes the default map scale factor used for the Polar
        Stereographic [0.9996], UTM [0.9996], and Transverse Mercator [1]
        projections in order to minimize areal distortion. Provide a new
        scale-factor or leave as default.

.. _PostScript Parameters:

PostScript Parameters
~~~~~~~~~~~~~~~~~~~~~

.. glossary::

    **PS_CHAR_ENCODING**
        (static) Names the eight bit character set being used for text in
        files and in command line parameters. This allows GMT to ensure
        that the PostScript output generates the correct characters on the
        plot. Choose from Standard, Standard+, ISOLatin1, ISOLatin1+, and
        ISO-8859-x (where x is in the ranges [1,10] or [13,15]). See
        Appendix F for details [ISOLatin1+ (or Standard+)].  **Note**: Normally
        the character set is written as part of the PostScript header.  If
        you need to switch to another character set for a later overlay then
        you must use **--PS_CHAR_ENCODING**\ =\ *encoding* on the command line and
        not via gmt set.

    **PS_COLOR_MODEL**
        Determines whether PostScript output should use RGB, HSV, CMYK, or
        GRAY when specifying color [rgb]. Note if HSV is selected it does
        not apply to images which in that case uses RGB. When selecting
        GRAY, all colors will be converted to gray scale using YIQ
        (television) conversion.

    **PS_COMMENTS**
        (static) If true we will issue comments in the PostScript file
        that explain the logic of operations. These are useful if you need
        to edit the file and make changes; otherwise you can set it to false
        which yields a somewhat slimmer PostScript file [false].

    **PS_CONVERT**
        Comma-separated list of optional module arguments that we should
        supply when :doc:`psconvert` is called implicitly under modern mode [**A**].
        Ignored when psconvert is called on the command line explicitly.
        The option arguments must be listed without their leading option hyphen.

    **PS_IMAGE_COMPRESS**
        Determines if PostScript images are compressed using the Run-Length
        Encoding scheme (rle), Lempel-Ziv-Welch compression (lzw), DEFLATE
        compression (deflate[,level]), or not at all (none) [deflate,5]. When
        specifying deflate, the compression level (1–9) may optionally be
        appended.

    **PS_LINE_CAP**
        Determines how the ends of a line segment will be drawn. Choose
        among a *butt* cap (default) where there is no projection beyond the
        end of the path, a *round* cap where a semicircular arc with
        diameter equal to the line-width is drawn around the end points, and
        *square* cap where a half square of size equal to the line-width
        extends beyond the end of the path [butt].

    **PS_LINE_JOIN**
        Determines what happens at kinks in line segments. Choose among a
        *miter* join where the outer edges of the strokes for the two
        segments are extended until they meet at an angle (as in a picture
        frame; if the angle is too acute, a bevel join is used instead, with
        threshold set by :term:`PS_MITER_LIMIT`), *round* join where a
        circular arc is used to fill in the cracks at the kinks, and *bevel*
        join which is a miter join that is cut off so kinks are triangular in shape [miter].

    **PS_MEDIA**
        *Classic mode:* Sets the physical size of the current plotting paper [a4 or letter].
        *Modern mode:* If user selects PostScript output then the above applies as well.
        For other graphics formats (PDF and rasters), the media size is determined automatically
        by cropping to fit the plot exactly (but see :term:`PS_CONVERT`).  However,
        if a specific media size is desired then the :term:`PS_MEDIA` may be specified as well.
        The following formats (and their widths and heights in points) are recognized:

        ======== ======== ======== ========== ======== ========
        Media    width    height   Media      width    height
        ======== ======== ======== ========== ======== ========
        A0       2380     3368     archA        648     864
        A1       1684     2380     archB        864     1296
        A2       1190     1684     archC        1296    1728
        A3       842      1190     archD        1728    2592
        A4       595      842      archE        2592    3456
        A5       421      595      flsa         612     936
        A6       297      421      halfletter   396     612
        A7       210      297      statement    396     612
        A8       148      210      note         540     720
        A9       105      148      letter       612     792
        A10      74       105      legal        612     1008
        B0       2836     4008     11x17        792     1224
        B1       2004     2836     tabloid      792     1224
        B2       1418     2004     ledger       1224    792
        B3       1002     1418
        B4       709      1002
        B5       501      709
        ======== ======== ======== ========== ======== ========

        For a completely custom format (e.g., for large format plotters) you
        may also specify WxH, where W and H are in points unless you append
        a unit to each dimension (**c**, **i**, **m** or **p** [Default]).
        Additional user-specific formats may be saved as separate line in a
        gmt_custom_media.conf file stored in ~/.gmt.  Each record would have a
        format name followed by width and height of your media in points.  For
        infinitely long paper rolls (e.g., plotters you can set height = 0).

    **PS_MITER_LIMIT**
        Sets the threshold angle in degrees (integer in range [0,180]) used
        for mitered joins only. When the angle between joining line segments
        is smaller than the threshold the corner will be bevelled instead of
        mitered. The default threshold is 35 degrees. Setting the threshold
        angle to 0 implies the PostScript default of about 11 degrees.
        Setting the threshold angle to 180 causes all joins to be beveled.

    **PS_PAGE_COLOR**
        Sets the color of the imaging background, i.e., the paper [white].

    **PS_PAGE_ORIENTATION**
        (**-P**) Sets the orientation of the page. Choose portrait or
        landscape [landscape].  Only available in GMT classic mode.

    **PS_SCALE_X**
        Global x-scale (> 0) to apply to plot-coordinates before plotting.
        Normally used to shrink the entire output down to fit a specific
        height/width [1.0].

    **PS_SCALE_Y**
        Global y-scale (> 0) to apply to plot-coordinates before plotting.
        Normally used to shrink the entire output down to fit a specific
        height/width [1.0].

    **PS_TRANSPARENCY**
        Sets the transparency mode to use when preparing PS for rendering to
        PDF. Choose from Color, ColorBurn, ColorDodge, Darken, Difference,
        Exclusion, HardLight, Hue, Lighten, Luminosity, Multiply, Normal,
        Overlay, Saturation, SoftLight, and Screen [Normal].

.. _Calendar/Time Parameters:

Calendar/Time Parameters
~~~~~~~~~~~~~~~~~~~~~~~~

.. glossary::

    **TIME_EPOCH**
        Specifies the value of the calendar and clock at the origin (zero
        point) of relative time units (see :term:`TIME_UNIT`). It is a string
        of the form yyyy-mm-ddT[hh:mm:ss] (Gregorian) or
        yyyy-Www-ddT[hh:mm:ss] (ISO) Default is 1970-01-01T00:00:00, the
        origin of the UNIX time epoch.

    **TIME_INTERVAL_FRACTION**
        Determines if partial intervals at the start and end of an axis
        should be annotated. If the range of the partial interval exceeds
        the specified fraction of the normal interval stride we will place
        the annotation centered on the partial interval [0.5].

    **TIME_IS_INTERVAL**
        Used when input calendar data should be truncated and adjusted to
        the middle of the relevant interval. In the following discussion,
        the unit *unit* can be one of these time units: (**y** year, **o**
        month, **u** ISO week, **d** day, **h** hour, **m** minute, and
        **s** second). **TIME_IS_INTERVAL** can have any of the following
        three values: (1) OFF [Default]. No adjustment, time is decoded as
        given. (2) +\ *n*\ *unit*. Activate interval adjustment for input by
        truncate to previous whole number of *n* units and then center time
        on the following interval. (3) -*n*\ *unit*. Same, but center time on
        the previous interval. For example, with **TIME_IS_INTERVAL** =
        +1o, an input data string like 1999-12 will be interpreted to mean
        1999-12-15T12:00:00.0 (exactly middle of December), while if
        **TIME_IS_INTERVAL** = off then that date is interpreted to mean
        1999-12-01T00:00:00.0 (start of December) [off].

    **TIME_REPORT**
        Controls if a time-stamp should be issued at start of all progress
        reports.  Choose among **clock** (absolute time stamp),
        **elapsed** (time since start of session), or **none**
        [none].

    **TIME_SYSTEM**
        Shorthand for a combination of :term:`TIME_EPOCH` and :term:`TIME_UNIT`,
        specifying which time epoch the relative time refers to and what the
        units are. Choose from one of the preset systems below (epoch and
        units are indicated):

        ============ ====================== =========== =====================
        TIME_SYSTEM  TIME_EPOCH             TIME_UNIT   Notes
        ============ ====================== =========== =====================
        JD           -4713-11-25T12:00:00   d           Julian Date
        MJD          1858-11-17T00:00:00    d           Modified Julian Date
        J2000        2000-01-01T12:00:00    d           Astronomical time
        S1985        1985-01-01T00:00:00    s           Altimetric time
        UNIX         1970-01-01T00:00:00    s           UNIX time
        RD0001       0001-01-01T00:00:00    s
        RATA         0000-12-31T00:00:00    d
        ============ ====================== =========== =====================

        This parameter is not stored in the **gmt.conf** file but is
        translated to the respective values of :term:`TIME_EPOCH` and
        :term:`TIME_UNIT`.

    **TIME_UNIT**
        Specifies the units of relative time data since epoch (see
        :term:`TIME_EPOCH`). Choose **y** (year - assumes all years are 365.2425
        days), **o** (month - assumes all months are of equal length y/12), **d**
        (day), **h** (hour), **m** (minute), or **s** (second) [**s**].

    **TIME_WEEK_START**
        When weeks are indicated on time axes, this parameter determines the
        first day of the week for Gregorian calendars. (The ISO weekly
        calendar always begins weeks with Monday.) [Monday (or Sunday)].

    **TIME_Y2K_OFFSET_YEAR**
        When 2-digit years are used to represent 4-digit years (see various
        **FORMAT_DATE**\ s), :term:`TIME_Y2K_OFFSET_YEAR` gives the first
        year in a 100-year sequence. For example, if
        :term:`TIME_Y2K_OFFSET_YEAR` is 1729, then numbers 29 through 99
        correspond to 1729 through 1799, while numbers 00 through 28
        correspond to 1800 through 1828. [1950].

See Also
--------

:doc:`gmt` , :doc:`gmtdefaults` ,
:doc:`gmtcolors` , :doc:`gmtget` ,
:doc:`gmtset`
