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PDL::Graphics::Gnuplot - Gnuplot-based plotting for PDL


 pdl> use PDL::Graphics::Gnuplot;

 pdl> $x = sequence(101) - 50;
 pdl> gplot($x**2);
 pdl> gplot($x**2,{xr=>[0,50]});

 pdl> gplot( {title => 'Parabola with error bars'},
       with => 'xyerrorbars', legend => 'Parabola',
       $x**2 * 10, abs($x)/10, abs($x)*5 );

 pdl> $xy = zeroes(21,21)->ndcoords - pdl(10,10);
 pdl> $z = inner($xy, $xy);
 pdl> gplot({title  => 'Heat map',
             trid   => 1,
             view   => [0,0]
            with => 'image', xvals($z),yvals($z),zeroes($z),$z*2

 pdl> $w = gpwin();                             # constructor
 pdl> $pi    = 3.14159;
 pdl> $theta = zeroes(200)->xlinvals(0, 6*$pi);
 pdl> $z     = zeroes(200)->xlinvals(0, 5);
 pdl> $w->plot3d(cos($theta), sin($theta), $z);
 pdl> $w->terminfo();                           # get information


This module allows PDL data to be plotted using Gnuplot as a backend for 2D and 3D plotting and image display. Gnuplot (not affiliated with the Gnu project) is a venerable, open-source program that produces both interactive and publication-quality plots on many different output devices. It is available through most Linux repositories, on MacOS, and from its website http://www.gnuplot.info.

It is not necessary to understand the gnuplot syntax to generate basic, or even complex, plots - though the full syntax is available for advanced users who want the full flexibility of the Gnuplot backend.

Gnuplot recognizes both hard-copy and interactive plotting devices, and on interactive devices (like X11) it is possible to pan, scale, and rotate both 2-D and 3-D plots interactively. You can also enter graphical data through mouse clicks on the device window. On some hardcopy devices (e.g. "PDF") that support multipage output, it is necessary to close the device after plotting to ensure a valid file is written out.

PDL::Graphics::Gnuplot exports two routines by default: a constructor, gpwin() and a general purpose plot routine, gplot(). Depending on options, gplot() can produce line plots, scatterplots, error boxes, "candlesticks", images, or any overlain combination of these elements; or perspective views of 3-D renderings such as surface plots.

A call to gplot() looks like:

 gplot({temp_plot_options}, # optional hash ref
      curve_options, data, data, ... ,
      curve_options, data, data, ... );

The data entries are columns to be plotted. They are normally an optional ordinate and a required abscissa, but some plot modes can use more columns than that. The collection of columns is called a "tuple". Each column must be a separate PDL or an ARRAY ref. If all the columns are PDLs, you can add extra dimensions to make threaded collections of curves.

PDL::Graphics::Gnuplot also implements an object oriented interface. Plot objects track individual gnuplot subprocesses. Direct calls to gplot() are tracked through a global object that stores globally set configuration variables.

The gplot() sub (or the plot() method) collects two kinds of options hash: plot options, which describe the overall structure of the plot being produced (e.g. axis specifications, window size, and title), and curve options, which describe the behavior of individual traces or collections of points being plotted. In addition, the module itself supports options that allow direct pass-through of plotting commands to the underlying gnuplot process.

Basic plotting

Gnuplot generates many kinds of plot, from basic line plots and histograms to scaled labels. Individual plots can be 2-D or 3-D, and different sets of plot styles are supported in each mode. Plots can be sent to a variety of devices; see the description of plot options, below.

You can specify what type of graphics output you want, but in most cases doing nothing will cause a plot to be rendered on your screen: with X windows on UNIX or Linux systems, with an XQuartz windows on MacOS, or with a native window on Microsoft Windows.

You select a plot style with the "with" curve option, and feed in columns of data (usually ordinate followed by abscissa). The collection of columns is called a "tuple". These plots have two columns in their tuples:

 $x = xvals(51)-25; $y = $x**2;
 gplot(with=>'points', $x, $y);  # Draw points on a parabola
 gplot(with=>'lines', $x, $y);   # Draw a parabola
 gplot({title=>"Parabolic fit"},
       with=>"yerrorbars", legend=>"data", $x, $y+(random($y)-0.5)*2*$y/20, pdl($y/20),
       with=>"lines",      legend=>"fit",  $x, $y);

Normal threading rules apply across the arguments to a given plot.

All data are required to be supplied as either PDLs or list refs. If you use a list ref as a data column, then normal threading is disabled. For example:

 $x = xvals(5);
 $y = xvals(5)**2;
 $labels = ['one','two','three','four','five'];

See below for supported curve styles.

Modifying plots

Gnuplot is built around a monolithic plot model - it is not possible to add new data directly to a plot without redrawing the entire plot. To support replotting, PDL::Graphics::Gnuplot stores the data you plot in the plot object, so that you can add new data with the "replot" command:


For speed, the data are *not* disconnected from their original variables - so this will plot X vs. sqrt(X):

 $x = xvals(101)/100;
 $y = xvals(101)/100;

Plotting to an image file or device

PDL:Graphics::Gnuplot can plot to most of the devices supported by gnuplot itself. You can specify the file type with the "output" method or the object constructor "gplot". Either one will allow you to name a type of file to produce, and a collection of options speciic to that type of output file.

Image plotting

Several of the plot styles accept image data. The tuple parameters work the same way as for basic plots, but each "column" is a 2-D PDL rather than a 1-D PDL. As a special case, the "with image" plot style accepts either a 2-D or a 3-D PDL. If you pass in 3-D PDL, the extra dimension can have size 1, 3, or 4. It is interpreted as running across (R,G,B,A) color planes.

3-D plotting

You can plot in 3-D by setting the plot option trid to a true value. Three dimensional plots accept either 1-D or 2-D PDLs as data columns. If you feed in 2-D "columns", many of the common plot styles will generalize appropriately to 3-D. For example, to plot a 2-D surface as a line grid, you can use the "lines" style and feed in 2-D columns instead of 1-D columns.

Enhanced text

Most gnuplot output devices include the option to markup "enhanced text". That means text is interpreted so that you can change its font and size, and insert superscripts and subscripts into labels. Codes are:


Text grouping - enclose text in braces to group characters, as in LaTeX.


Superscript the next character or group (shrinks it slightly too where that is supported).


Subscript the next character or group (shrinks it slightly too where that is supported).


Phantom box (occupies no width; controls height for super- and subscripting)


Controllable-width space, e.g. &{template-string}


overstrike -- e.g. ~a{0.8-} overprints '-' on 'a', raised by 0.8xfontsize.

{/[fontname][=fontsize | *fontscale] text}

Change font to (optional) fontname, and optional absolute font size or relative font scale ("fontsize" and "fontscale" are numbers). The space after the size parameter is not rendered.


Backslash escapes control characters to render them as themselves.

Color specification

There are several contexts where you can specify color of plot elements. In those places, you can specify colors exactly as in the Gnuplot manual, or more tersely. In general, a color spec can be any one of the following:

- an integer

This specifies a recognizable unique color in the same order as used by the plotting engine.

- the name of a color

(e.g. "blue"). Supported color names are listed in the variable @Alien::Gnuplot::colors.

- an RGB value string

Strings have the form #RRGGBB, where the # is literal and the RR, GG, and BB are hexadecimal bytes.

- the word "palette"

"palette" indicates that color is to be drawn from the scaled colorbar palette (which you can set with the "clut" plot option), by lookup using an additional column in the associated data tuple.

- the word "variable"

"variable" indicates that color is to be drawn from the integer plotting colors used by the plotting engine, indexed by an additional column in the associated data tuple.

- the phrase "rgb variable"

"rgb variable" indicates that color is to be directly specified by a 24 bit integer specifying 8-bit values for (from most significant byte to least significant byte) R, G, and B in the output color. The integer is drawn from an additional column in the associated data tuple.

Plot styles supported

Gnuplot itself supports a wide range of plot styles, and all are supported by PDL::Graphics::Gnuplot. Most of the basic plot styles collect tuples of 1-D columns in 2-D mode (for ordinary plots), or either 1-D or 2-D "columns" in 3-D mode (for grid surface plots and such). Image modes always collect tuples made of 2-D "columns".

You can pass in 1-D columns as either PDLs or ARRAY refs. That is important for plot types (such as "labels") that require a collection of strings rather than numeric data.

Each plot style can by modified to support particular colors or line style options. These modifications get passed in as curve options (see below). For example, to plot a blue line you can use with=>'lines',lc=>'blue'. To match the autogenerated style of a particular line you can use the ls curve option.

The GNuplot plot styles supported are:

  • boxerrorbars - combo of boxes and yerrorbars, below (2D)

  • boxes - simple boxes around regions on the plot (2D)

  • boxxyerrorbars - Render X and Y error bars as boxes (2D)

  • candlesticks - Y error bars with inner and outer limits (2D)

  • circles - circles with variable radius at each point: X/Y/radius (2D)

  • dots - tiny points ("dots") at each point, e.g. for scatterplots (2D/3D)

  • ellipses - ellipses. Accepts X/Y/major/minor/angle (2D)

  • filledcurves - closed polygons or axis-to-line filled shapes (2D)

  • financebars - financial style plot. Accepts date/open/low/high/close (2D)

  • fsteps - square bin plot; delta-Y, then delta-X (see steps, histeps) (2D)

  • histeps - square bin plot; plateaus centered on X coords (see fsteps, steps) (2D)

  • histogram - binned histogram of dataset (not direct plot; see newhistogram) (2D)

  • fits - (PDL-specific) renders FITS image files in scientific coordinates

  • image - Takes (i), (x,y,i), or (x,y,z,i). See rgbimage, rgbalpha, fits. (2D/3D)

  • impulses - vertical line from axis to the plotted point (2D/3D)

  • labels - Text labels at specified locations all over the plot (2D/3D)

  • lines - regular line plot (2D/3D)

  • linespoints - line plot with symbols at plotted points (2D/3D)

  • newhistogram - multiple-histogram-friendly histogram style (see histogram) (2D)

  • points - symbols at plotted points (2D/3D)

  • rgbalpha - R/G/B color image with variable transparency (2D/3D)

  • rgbimage - R/G/B color image (2D/3D)

  • steps - square bin plot; delta-X, then delta-Y (see fsteps, histeps) (2D)

  • vectors - Small arrows: (x,y,[z]) -> (x+dx,y+dy,[z+dz]) (2D/3D)

  • xerrorbars - points with X error bars ("T" form) (2D)

  • xyerrorbars - points with both X and Y error bars ("T" form) (2D)

  • yerrorbars - points with Y error bars ("T" form) (2D)

  • xerrorlines - line plot with X errorbars at each point. (2D)

  • xyerrorlines - line plot with XY errorbars at each point. (2D)

  • yerrorlines - line plot with Y error limits at each point. (2D)

  • pm3d - three-dimensional variable-position surface plot

Options arguments

The plot options are parameters that affect the whole plot, like the title of the plot, the axis labels, the extents, 2d/3d selection, etc. All the plot options are described below in "Plot Options". Plot options can be set in the plot object, or passed to the plotting methods directly. Plot options can be passed in as a leading interpolated hash, as a leading hash ref, or as a trailing hash ref in the argument list to any of the main plotting routines (gplot, plot, image, etc.).

The curve options are parameters that affect only one curve in particular. Each call to plot() can contain many curves, and options for a particular curve precede the data for that curve in the argument list. The actual type of curve (the "with" option) is persistent, but all other curve options and modifiers are not. An example:

 gplot( with => 'points',  $x, $a,
        {axes=> x1y2},     $x, $b,
        with => 'lines',   $x, $c );

This plots 3 curves: $a vs. $x plotted with points on the main y-axis (this is the default), $b vs. $x plotted with points on the secondary y axis, and $c vs. $x plotted with lines on the main y-axis (the default). Note that the curve options can be supplied as either an inline hash or a hash ref.

All the curve options are described below in "Curve Options".

If you want to plot multiple curves of the same type without setting any curve options explicitly, you must include an empty hash ref between the tuples for subsequent lines, as in:

 gplot( $x, $a, {}, $x, $b, {}, $x, $c );

Data arguments

Following the curve options in the plot() argument list is the actual data being plotted. Each output data point is a "tuple" whose size varies depending on what is being plotted. For example if we're making a simple 2D x-y plot, each tuple has 2 values; if we're making a 3d plot with each point having variable size and color, each tuple has 5 values (x,y,z,size,color). Each tuple element must be passed separately. For ordinary 2-D plots, the 0 dim of the tuple elements runs across plotted point. PDL threading is active, so you can plot multiple curves with similar curve options on a normal 2-D plot, just by stacking data inside the passed-in PDLs. (An exception is that threading is disabled if one or more of the data elements is a list ref).

PDLs vs list refs

The usual way to pass in data is as a PDL -- one PDL per column of data in the tuple. But strings, in particular, cannot easily be hammered into PDLs. Therefore any column in each tuple can be a list ref containing values (either numeric or string). The column is interpreted using the usual polymorphous cast-behind-your-back behavior of Perl. For the sake of sanity, if even one list ref is present in a tuple, then threading is disabled in that tuple: everything has to have a nice 1-D shape.

Implicit domains

When making a simple 2D plot, if exactly 1 dimension is missing, PDL::Graphics::Gnuplot will use sequence(N) as the domain. This is why code like plot(pdl(1,5,3,4,4) ) works. Only one PDL is given here, but the plot type ("lines" by default) requires 2 elements per tuple. We are thus exactly 1 piddle short; sequence(5) is used as the missing domain PDL. This is thus equivalent to plot(sequence(5), pdl(1,5,3,4,4) ).

If plotting in 3d or displaying an image, an implicit domain will be used if we are exactly 2 piddles short. In this case, PDL::Graphics::Gnuplot will use a 2D grid as a domain. Example:

 my $xy = zeros(21,21)->ndcoords - pdl(10,10);
 gplot({'3d' => 1},
        with => 'points', inner($xy, $xy));
 gplot( with => 'image',  sin(rvals(51,51)) );

Here the only given piddle has dimensions (21,21). This is a 3D plot, so we are exactly 2 piddles short. Thus, PDL::Graphics::Gnuplot generates an implicit domain, corresponding to a 21-by-21 grid.

PDL::Graphics::Gnuplot requires explicit separators between tuples for different plots, so it is always clear from the arguments you pass in just how many columns you are supplying. For example, plot($a,$b) will plot $b vs. $a. If you actually want to plot an overlay of both $a and $b against array index, you want plot($a,{},$b) instead. The {} is a hash ref containing a collection of all the curve options that you are changing between the two curves -- in this case, zero of them.


PDL::Graphics::Gnuplot supports four styles of image plot, via the "with" curve option.

The "image" style accepts a single image plane and displays it using the palette (pseudocolor map) that is specified in the plot options for that plot. As a special case, if you supply as data a (3xWxH) or (WxHx3) PDL it is treated as an RGB image and displayed with the "rgbimage" style (below), provided there are at least 5 pixels in each of the other two dimensions (just to be sure). For quick image display there is also an "image" method:

 use PDL::Graphics::Gnuplot qw/image gplot/;
 $im = sin(rvals(51,51)/2);
 image( $im );                # display the image
 gplot( with=>'image', $im );  # display the image (longer form)

The colors are autoscaled in both cases. To set a particular color range, use the 'cbrange' plot option:

 image( {cbrange=>[0,1]}, $im );

You can plot rgb images directly with the image style, just by including a 3rd dimension of size 3 on your image:

 $rgbim = pdl( xvals($im), yvals($im),rvals($im)/sqrt(2));
 image( $rgbim );                # display an RGB image
 gplot( with=>'image', $rgbim ); # display an RGB image (longer form)

Some additional plot styles exist to specify RGB and RGB transparent forms directly. These are the "with" styles "rgbimage" and "rgbalpha". For each of them you must specify the channels as separate PDLs:

 gplot( with=>'rgbimage', $rgbim->dog );               # RGB  the long way
 gplot( with=>'rgbalpha', $rgbim->dog, 255*($im>0) );  # RGBA the long way

According to the gnuplot specification you can also give X and Y values for each pixel, as in

 gplot( with=>'image', xvals($im), yvals($im), $im )

but this appears not to work properly for anything more complicated than a trivial matrix of X and Y values.

PDL::Graphics::Gnuplot provides a "fits" plot style that interprets World Coordinate System (WCS) information supplied in the header of the scientific image format FITS. The image is displayed in rectified scientific coordinates, rather than in pixel coordinates. You can plot FITS images in scientific coordinates with

 gplot( with=>'fits', $fitsdata );

The fits plot style accepts a modifier "resample" (which may be abbreviated), that allows you to downsample and/or rectify the image before it is passed to the Gnuplot back-end. This is useful either to cut down on the burden of transferring large blocks of image data or to rectify images with nonlinear WCS transformations in their headers. (gnuplot itself has a bug that prevents direct rendering of images in nonlinear coordinates).

 gplot( with=>'fits res 200', $fitsdata );
 gplot( with=>'fits res 100,400',$fitsdata );

to specify that the output are to be resampled onto a square 200x200 grid or a 100x400 grid, respectively. The resample sizes must be positive integers.


Several of the graphical backends of Gnuplot are interactive, allowing you to pan, zoom, rotate and measure the data interactively in the plot window. See the Gnuplot documentation for details about how to do this. Some terminals (such as wxt) are persistently interactive. Other terminals (such as x11) maintain their interactivity only while the underlying gnuplot process is active -- i.e. until another plot is created with the same PDL::Graphics::Gnuplot object, or until the perl process exits (whichever comes first). Still others (the hardcopy devices) aren't interactive at all.

Some interactive devices (notably wxt and x11) also support mouse input: you can write PDL scripts that accept and manipulate graphical input from the plotted window.


Gnuplot controls plot style with "plot options" that configure and specify virtually all aspects of the plot to be produced. Plot options are tracked as stored state in the PDL::Graphics::Gnuplot object. You can set them by passing them in to the constructor, to an options method, or to the plot method itself.

Nearly all the underlying Gnuplot plot options are supported, as well as some additional options that are parsed by the module itself for convenience.

There are many, many plot options. For convenience, we've grouped them by general category below. Each group has a heading "POs for <foo>", describing the category. You can skip below them all if you want to read about curve options or other aspects of PDL::Graphics::Gnuplot.

POs for Output: terminal, termoption, output, device, hardcopy

You can send plots to a variety of different devices; Gnuplot calls devices "terminals". With the object-oriented interface, you must set the output device with the constructor PDL::Graphics::Gnuplot::new (or the exported constructor gpwin) or the output method. If you use the simple non-object interface, you can set the output with the terminal, termoption, and output plot options.

terminal sets the output device type for Gnuplot, and output sets the actual output file or window number.

device and hardcopy are for convenience. device offers a PGPLOT-style device specifier in "filename/device" format (the "filename" gets sent to the "output" option, the "device" gets sent to the "terminal" option). hardcopy takes an output file name, attempts to parse out a file suffix and infer a device type. hardcopy also uses a common set of terminal options needed to fill an entire letter page with a plot.

For finer grained control of the plotting environment, you can send "terminal options" to Gnuplot. If you set the terminal directly with plot options, you can include terminal options by interpolating them into a string, as in terminal jpeg interlace butt crop, or you can use the constructor new (also exported as gpwin), which parses terminal options as an argument list.

The routine PDL::Graphics::Gnuplot::terminfo prints a list of all available terminals or, if you pass in a terminal name, options accepted by that terminal.

POs for Titles

The options described here are


Gnuplot supports "enhanced" text escapes on most terminals; see "text", below.

The title option lets you set a title for the whole plot.

Individual plot components are labeled with the label options. xlabel, x2label, ylabel, and y2label specify axis titles for 2-D plots. The zlabel works for 3-D plots. The cblabel option sets the label for the color box, in plot types that have one (e.g. image display).

(Don't be confused by clabel, which doesn't set a label at all, rather specifies the printf format used by contour labels in contour plots.)

key controls where the plot key (that relates line/symbol style to label) is placed on the plot. It takes a scalar boolean indicating whether to turn the key on (with default values) or off, or a list ref containing any of the following arguments (all are optional) in the order listed:

  • ( on | off ) - turn the key on or off

  • ( inside | outside | lmargin | rmargin | tmargin | bmargin | at <pos> )

    These keywords set the location of the key -- "inside/outside" is relative to the plot border; the margin keywords indicate location in the margins of the plot; and at <pos> (where <pos> is a comma-delimited string containing (x,y): key=>[at=>"0.5,0.5"]) is an exact location to place the key.

  • ( left | right | center ) ( top | bottom | center ) - horiz./vert. alignment

  • ( vertical | horizontal ) - stacking direction within the key

  • ( Left | Right ) - justification of plot labels within the key (note case)

  • [no]reverse - switch order of label and sample line

  • [no]invert - invert the stack order of the labels

  • samplen <length> - set the length of the sample lines

  • spacing <dist> - set the spacing between adjacent labels in the list

  • [no]autotitle - control whether labels are generated when not specified

  • title "<text>" - set a title for the key

  • [no]enhanced - override terminal settings for enhanced text interpretation

  • font "<face>,<size>" - set font for the labels

  • textcolor <colorspec>

  • [no]box linestyle <ls> linetype <lt> linewidth <lw> - control box around the key

POs for axes, grids, & borders

The options described here are


Normally, tick marks and their labels are applied to the border of a plot, and no extra axes (e.g. the y=0 line) nor coordinate grids are shown. You can specify which (if any) zero axes should be drawn, and which (if any) borders should be drawn.

The border option controls whether the plot itself has a border drawn around it. You can feed it a scalar boolean value to indicate whether borders should be drawn around the plot -- or you can feed in a list ref containing options. The options are all optional but must be supplied in the order given.

  • <integer> - packed bit flags for which border lines to draw

    The default if you set a true value for border is to draw all border lines. You can feed in a single integer value containing a bit mask, to draw only some border lines. From LSB to MSB, the coded lines are bottom, left, top, right for 2D plots -- e.g. 5 will draw bottom and top borders but neither left nor right.

    In three dimensions, 12 bits are used to describe the twelve edges of a cube surrounding the plot. In groups of three, the first four control the bottom (xy) plane edges in the same order as in the 2-D plots; the middle four control the vertical edges that rise from the clockwise end of the bottom plane edges; and the last four control the top plane edges.

  • ( back | front ) - draw borders first or last (controls hidden line appearance)

  • linewidth <lw>, linestyle <ls>, linetype <lt>

    These are Gnuplot's usual three options for line control.

The grid option indicates whether gridlines should be drawn on each axis. It takes a list ref of arguments, each of which is either "no" or "m" or "", followed by an axis name and "tics" -- e.g. grid=>["noxtics","ymtics"] draws no X gridlines and draws (horizontal) Y gridlines on Y axis major and minor tics, while grid=>["xtics","ytics"] or grid=>["xtics ytics"] will draw both vertical (X) and horizontal (Y) grid lines on major tics.

To draw a coordinate grid with default values, set grid=>1. For more control, feed in a list ref with zero or more of the following parameters, in order:

The zeroaxis keyword indicates whether to actually draw each axis line at the corresponding zero along its indicated dimension. For example, to draw the X axis (y=0), use xzeroaxis=>1. If you just want the axis turned on with default values, you can feed in a Boolean scalar; if you want to set its parameters, you can feed in a list ref containing linewidth, linestyle, and linetype (with appropriate parameters for each), e.g. xzeroaxis=>[linewidth=>2].

POs for axis range and mode

The options described here are


Gnuplot accepts explicit ranges as plot options for all axes. Each option accepts a list ref with (min, max). If either min or max is missing, then the opposite limit is autoscaled. The x and y ranges refer to the usual ordinate and abscissa of the plot; x2 and y2 refer to alternate ordinate and abscissa; z if for 3-D plots; r is for polar plots; t, u, and v are for parametric plots. cb is for the color box on plots that include it (see "color", below).

rrange is used for radial coordinates (which are accessible using the mapping plot option, below).

cbrange (for 'color box range') sets the range of values over which palette colors (either gray or pseudocolor) are matched. It is valid in any color-mapped plot (including images or palette-mapped lines or points), even if no color box is being displayed for this plot.

trange, urange, and vrange set ranges for the parametric coordinates if you are plotting a parametric curve.

By default all axes are autoscaled unless you specify a range on that axis, and partially (min or max) autoscaled if you specify a partial range on that axis. autoscale allows more explicit control of how autoscaling is performed, on an axis-by-axis basis. It accepts a hash ref, each element of which specifies how a single axis should be autoscaled. Each keyword contains an axis name followed by one of "fix", "min", "max", "fixmin", or "fixmax". You can set all the axes at once by setting the keyword name to ' '. Examples:


There is an older list ref syntax which is deprecated but still accepted.

To not autoscale an axis at all, specify a range for it. The fix style of autoscaling forces the autoscaler to use the actual min/max of the data as the limit for the corresponding axis -- by default the axis gets extended to the next minor tic (as set by the autoticker or by a tic specification, see below).

logscale allows you to turn on logarithmic scaling for any or all axes, and to set the base of the logarithm. It takes a list ref, the first element of which is a string mushing together the names of all the axes to scale logarithmically, and the second of which is the base of the logarithm: logscale=>[xy=>10]. You can also leave off the base if you want base-10 logs: logscale=>['xy'].

POs for Axis tick marks

The options described here are


Axis tick marks are called "tics" within Gnuplot, and they are extensively controllable via the "{axis}tics" options. In particular, major and minor ticks are supported, as are arbitrarily variable length ticks, non-equally spaced ticks, and arbitrarily labelled ticks. Support exists for time formatted ticks (see POs for time data values below).

By default, gnuplot will automatically place major and minor ticks. You can turn off ticks on an axis by setting the appropriate {foo}tics option to a defined, false scalar value (e.g. xtics=>0). If you want to set major tics to happen at a regular specified intervals, you can set the appropriate tics option to a nonzero scalar value (e.g. xtics=>2 to specify a tic every 2 units on the X axis). To use default values for the tick positioning, specify an empty hash or array ref (e.g. xtics=>{}), or a string containing only whitespace (e.g. xtics=>' ').

If you prepend an 'm' to any tics option, it affects minor tics instead of major tics (major tics typically show units; minor tics typically show fractions of a unit).

Each tics option can accept a hash ref containing options to pass to Gnuplot. You can also pass in a snippet of gnuplot command, as either a string or an array ref -- but those techniques are deprecated and may disappear in a future version of PDL:Graphics::Gnuplot.

The keywords are case-insensitive and may be abbreviated, just as with other option types. They are:

  • axis - set to 1 to place tics on the axis (the default)

  • border - set to 1 to place tics on the border (not the default)

  • mirror - set to 1 to place mirrored tics on the opposite axis/border (the default, unless an alternate axis interferes -- e.g. y2)

  • in - set to 1 to draw tics inward from the axis/border

  • out - set to 1 to draw tics outward from the axis/border

  • scale - multiplier on tic length compared to the default

    If you pass in undef, tics get the default length. If you pass in a scalar, major tics get scaled. You can pass in an array ref to scale minor tics too.

  • rotate - turn label text by the given angle (in degrees) on the drawing plane

  • offset - offset label text from default position, (units: characters; requires array ref containing x,y)

  • locations - sets tic locations. Gets an array ref: [incr], [start, incr], or [start, incr, stop].

  • labels - sets tic locations explicitly, with text labels for each. If you specify both locations and labels, you get both sets of tics on the same axis.

    The labels should be a nested list ref that is a collection of duals or triplets. Each dual or triplet should contain [label, position, minorflag], as in labels=>[["one",1,0],["three-halves",1.5,1],["two",2,0]].

  • format - printf-style format string for tic labels. There are some extensions to the gnuplot format tags -- see the gnuplot manual. Gnuplot 4.8 and higher have %h, which works like %g but uses extended text formatting if it is available.

  • font - set font name and size (system font name)

  • rangelimited - set to 1 to limit tics to the range of values actually present in the plot

  • textcolor - set the color of the ticks (see "color specs" below)

For example, to turn on inward mirrored X axis ticks with diagonal Arial 9 text, use:

 xtics => {axis=>1,mirror=>1,in=>1,rotate=>45,font=>'Arial,9'}


 xtics => ['axis','mirror','in','rotate by 45','font "Arial,9"']

POs for time data values

The options described here are


Gnuplot contains support for plotting absolute time and date on any of its axes, with conventional formatting. There are three main methods, which are mutually exclusive (i.e. you should not attempt to use two at once on the same axis).

Plotting timestamps using UNIX times

You can set any axis to plot timestamps rather than numeric values by setting the corresponding "data" plot option to "time", e.g. xdata=>"time". If you do so, then numeric values in the corresponding data are interpreted as UNIX time (seconds since the UNIX epoch, neglecting leap seconds). No provision is made for UT-TAI conversion. You can format how the times are plotted with the "format" option in the various "tics" options(above). Output specifiers should be in UNIX strftime(3) format -- for example, xdata=>"time",xtics=>{format=>"%Y-%b-%dT%H:%M:%S"} will plot UNIX times as ISO timestamps in the ordinate.

Due to limitations within gnuplot, the time resolution in this mode is limited to 1 second - if you want fractional seconds, you must use numerically formatted times (and/or create your own tick labels using the labels suboption to the ?tics option.

Timestamp format specifiers

Time format specifiers use the following printf-like codes:

  • Year A.D.: %Y is 4-digit year; %y is 2-digit year (1969-2068)

  • Month of year: %m: 01-12; %b or %h: abrev. name; %B: full name

  • Week of year: %W (week starting Monday); %U (week starting Sunday)

  • Day of year: %j (1-366; boundary is midnight)

  • Day of month: %d (01-31)

  • Day of week: %w (0-6, Sunday=0), %a (abrev. name), %A (full name)

  • Hour of day: %k (0-23); %H (00-23); %l (1-12); %I (01-12)

  • Am/pm: %p ("am" or "pm")

  • Minute of hour: %M (00-60)

  • Second of minute: %S (0-60)

  • Total seconds since start of 2000 A.D.: %s

  • Timestamps: %T (same as %H:%M:%S); %R (same as %H:%M); %r (same as %I:%M:%S %p)

  • Datestamps: %D (same as %m/%d/%y); %F (same as %Y-%m-%d)

  • ISO timestamps: use %DT%T.

day-of-week plotting

If you just want to plot named days of the week, you can instead use the dtics options set plotting to day of week, where 0 is Sunday and 6 is Saturday; values are interpreted modulo 7. For example, xmtics=>1,xrange=>[-4,9] will plot two weeks from Wednesday to Wednesday. As far as output format goes, this is exactly equivalent to using the %w option with full formatting - but you can treat the numeric range in terms of weeks rather than seconds.

month-of-year plotting

The mtics options set plotting to months of the year, where 1 is January and 12 is December, so xdtics=>1, xrange=>[0,4] will include Christmas through Easter. This is exactly equivalent to using the %d option with full formatting - but you can treat the numeric range in terms of months rather than seconds.

POs for location/size

The options described here are


Adjusting the size, location, and margins of the plot on the plotting surface is something of a null operation for most single plots -- but you can tweak the placement and size of the plot with these options. That is particularly useful for multiplots, where you might like to make an inset plot or to lay out a set of plots in a custom way.

The margin options accept scalar values -- either a positive number of character heights or widths of margin around the plot compared to the edge of the device window, or a string that starts with "at screen " and interpolates a number containing the fraction of the plot window offset. The "at screen" technique allows exact plot placement and is an alternative to the origin and size options below.

The offsets option allows you to put an empty boundary around the data, inside the plot borders, in an autosacaled graph. The offsets only affect the x1 and y1 axes, and only in 2D plot commands. offsets accepts a list ref with four values for the offsets, which are given in scientific (plotted) axis units.

The origin option lets you specify the origin (lower left corner) of an individual plot on the plotting window. The coordinates are screen coordinates -- i.e. fraction of the total plotting window.

The size option lets you adjust the size and aspect ratio of the plot, as an absolute fraction of the plot window size. You feed in fractional ratios, as in size=>[$xfrac, $yfrac]. You can also feed in some keywords to adjust the aspect ratio of the plot. The size option overrides any autoscaling that is done by the auto-layout in multiplot mode, so use with caution -- particularly if you are multiplotting. You can use "size" to adjust the aspect ratio of a plot, but this is deprecated in favor of the pseudo-option justify.

justify sets the scientific aspect ratio of a 2-D plot. Unity yields a plot with a square scientific aspect ratio. Larger numbers yield taller plots.

clip controls the border between the plotted data and the border of the plot. There are three clip types supported: points, one, and two. You can set them independently by passing in booleans with their names: clip=>[points=>1,two=>0].

POs for Color: colorbox, palette, clut, pseudocolor, pc, perceptual, pcp

Color plots are supported via RGB and pseudocolor. Plots that use pseudcolor or grayscale can have a "color box" that shows the photometric meaning of the color.

The colorbox generally appears when necessary but can be controlled manually with the colorbox option. colorbox accepts a scalar boolean value indicating whether or no to draw a color box, or a list ref containing additional options. The options are all, well, optional but must appear in the order given:

( vertical | horizontal ) - indicates direction of the gradient in the box
( default | user ) - indicates user origin and size

If you specify default the colorbox will be placed on the right-hand side of the plot; if you specify user, you give the location and size in subsequent arguments:

 colorbox => [ 'user', 'origin'=>"$x,$y", 'size' => "$x,$y" ]
( front | back ) - draws the colorbox before or after the plot
( noborder | bdefault | border <line style> ) - specify border

The line style is a numeric type as described in the gnuplot manual.

The palette option offers many arguments that are not fully documented in this version but are explained in the gnuplot manual. It offers complete control over the pseudocolor mapping function.

For simple color maps, clut gives access to a set of named color maps. (from "Color Look Up Table"). A few existing color maps are: "default", "gray", "sepia", "ocean", "rainbow", "heat1", "heat2", and "wheel". To see a complete list, specify an invalid table, e.g. clut=>'xxx'. clut is maintained but is superseded by pc and pcp (below), which give access to a better variety of color tables, and have better support for scientific images.

pseudocolor (synonym pc) gives access to the color tables built in to the PDL::Transform::Color package, if that package is available. It takes either a color table name or a list ref which is a collection of arguments that get sent to the PDL::Transform::Color::t_pc transform definition method. Sending the empty string or undef will generate a list of allowable color table names. Many of the color tables are "photometric" and will render photometric data correctly without gamma correction.

perceptual (synonym pcp) gives the same access to PDL::Transform::Color as does pseudocolor, but the "equal-perceptual-difference" scaling is used -- i.e. input values are gamma-corrected by the module so that uniform shifts in numeric value yield approximately uniform perceptual shifts.

If you use pseudocolor or perceptual, and if PDL::Transform::Color can be loaded, then the external module is used to define a custom Gnuplot palette by linear interpolation across 256 values. That palette is then used to translate your monochrome data to a color image. The Gnuplot output is assumed to be sRGB. This is probably OK for most output devices.

POs for 3D: trid, view, pm3d, hidden3d, dgrid3d, surface, xyplane, mapping

If trid or its synonym 3d is true, Gnuplot renders a 3-D plot. This changes the default tuple size from 2 to 3. This option is used to switch between the Gnuplot "plot" and "splot" command, but it is tracked with persistent state just as any other option.

The view option controls the viewpoint of the 3-D plot. It takes a list of numbers: view=>[$rot_x, $rot_z, $scale, $scale_z]. After each number, you can omit the subsequent ones. Alternatively, view=>['map'] represents the drawing as a map (e.g. for contour plots) and view=>[equal=>'xy'] forces equal length scales on the X and Y axes regardless of perspective, while view=>[equal=>'xyz'] sets equal length scales on all three axes.

The pm3d option accepts several parameters to control the pm3d plot style, which is a palette-mapped 3d surface. They are not documented here in this version of the module but are explained in the gnuplot manual.

hidden3d accepts a list of parameters to control how hidden surfaces are plotted (or not) in 3D. It accepts a boolean argument indicating whether to hide "hidden" surfaces and lines; or a list ref containing parameters that control how hidden surfaces and lines are handled. For details see the gnuplot manual.

xyplane sets the location of that plane (which is drawn) relative to the rest of the plot in 3-space. It takes a single string: "at" or "relative", and a number. xyplane=>[at=>$z] places the XY plane at the stated Z value (in scientific units) on the plot. xyplane=>[relative=>$frac] places the XY plane $frac times the length of the scaled Z axis *below* the Z axis (i.e. 0 places it at the bottom of the plotted Z axis; and -1 places it at the top of the plotted Z axis).

mapping takes a single string: "cartesian", "spherical", or "cylindrical". It determines the interpretation of data coordinates in 3-space. (Compare to the polar option in 2-D).

POs for Contour plots - contour, cntrparam

Contour plots are only implemented in 3D. To make a normal 2D contour plot, use 3-D mode, but set the view to "map" - which projects the 3-D plot onto its 2-D XY plane. (This is convoluted, for sure -- future versions of this module may have a cleaner way to do it).

contour enables contour drawing on surfaces in 3D. It takes a single string, which should be "base", "surface", or "both".

cntrparam manages how contours are generated and smoothed. It accepts a list ref with a collection of Gnuplot parameters that are issued one per line; refer to the Gnuplot manual for how to operate it.

POs for Polar plots - polar, angles, mapping

You can make 2-D polar plots by setting polar to a true value. The ordinate is then plotted as angle, and the abscissa is radius on the plot. The ordinate can be in either radians or degrees, depending on the angles parameter

angles takes either "degrees" or "radians" (default is radians).

mapping is used to set 3-D polar plots, either cylindrical or spherical (see the section on 3-D plotting, above).

POs for Markup - label, arrow, object

You specify plot markup in advance of the plot command, with plot options (or add it later with the replot method). The options give you access to a collection of (separately) numbered descriptions that are accumulated into the plot object. To add a markup object to the next plot, supply the appropriate options as a list ref or as a single string. To specify all markup objects at once, supply the appropriate options for all of them as a nested list-of-lists.

To modify an object, you can specify it by number, either by appending the number to the plot option name (e.g. arrow3) or by supplying it as the first element of the option list for that object.

To remove all objects of a given type, supply undef (e.g. arrow=>undef).

For example, to place two labels, use the plot option:

 label => [["Upper left",at=>"10,10"],["lower right",at=>"20,5"]];

To add a label to an existing plot object, if you don't care about what index number it gets, do this:

 $w->options( label=>["my new label",at=>[10,20]] );

If you do care what index number it gets (or want to replace an existing label), do this:

 $w->options( label=>[$n, "my replacement label", at=>"10,20"] );

where $w is a Gnuplot object and $n contains the label number you care about.

label - add a text label to the plot.

The label option allows adding small bits of text at arbitrary locations on the plot.

Each label specifier list ref accepts the following suboptions, in order. All of them are optional -- if no options other than the index tag are given, then any existing label with that index is deleted.

For examples, please refer to the Gnuplot 4.4 manual, p. 117.

<tag> - optional index number (integer)
<label text> - text to place on the plot.

You may supply double-quotes inside the string, but it is not necessary in most cases (only if the string contains just an integer and you are not specifying a <tag>.

at <position> - where to place the text (sci. coordinates)

The <position> should be a string containing a gnuplot position specifier. At its simplest, the position is just two numbers separated by a comma, as in label2=>["foo",at=>"5,3"], to specify (X,Y) location on the plot in scientific coordinates. Each number can be preceded by a coordinate system specifier; see the Gnuplot 4.4 manual (page 20) for details.

( left | center | right ) - text placement rel. to position
rotate [ by <degrees> ] - text rotation

If "rotate" appears in the list alone, then the label is rotated 90 degrees CCW (bottom-to-top instead of left-to-right). The following "by" clause is optional.

font "<name>,<size>" - font specifier

The <name>,<size> must be double quoted in the string (this may be fixed in a future version), as in

noenhanced - turn off gnuplot enhanced text processing (if enabled)
( front | back ) - rendering order (last or first)
textcolor <colorspec>
(point <pointstyle> | nopoint ) - control whether the exact position is marked
offset <offset> - offfset from position (in points).

arrow - place an arrow or callout line on the plot

Works similarly to the label option, but with an arrow instead of text.

The arguments, all of which are optional but which must be given in the order listed, are:

from <position> - start of arrow line

The <position> should be a string containing a gnuplot position specifier. At its simplest, the position is just two numbers separated by a comma, as in arrow2=>["foo",at=>"5,3"], to specify (X,Y) location on the plot in scientific coordinates. Each number can be preceded by a coordinate system specifier; see the Gnuplot 4.4 manual (page 20) for details.

( to | rto ) <position> - end of arrow line

These work like from. For absolute placement, use "to". For placement relative to the from position, use "rto".

(arrowstyle | as) <arrow_style>

This specifies that the arrow be drawn in a particular predeclared numerical style. If you give this parameter, you should omit all the following ones.

( nohead | head | backhead | heads ) - specify arrowhead placement
size <length>,<angle>,<backangle> - specify arrowhead geometry
( filled | empty | nofilled ) - specify arrowhead fill
( front | back ) - specify drawing order ( last | first )
linestyle <line_style> - specify a numeric linestyle
linetype <line_type> - specify numeric line type
linewidth <line_width> - multiplier on the width of the line

object - place a shape on the graph

objects are rectangles, ellipses, circles, or polygons that can be placed arbitrarily on the plotting plane.

The arguments, all of which are optional but which must be given in the order listed, are:

<object-type> <object-properties> - type name of the shape and its type-specific properties

The <object-type> is one of four words: "rectangle", "ellipse", "circle", or "polygon".

You can specify a rectangle with from=>$pos1, [r]to=>$pos2, with center=>$pos1, size=>"$w,$h", or with at=>$pos1,size=>"$w,$h".

You can specify an ellipse with at=>$pos, size=>"$w,$h" or center=>$pos, size=>"$w,$h", followed by angle=>$a.

You can specify a circle with at=>$pos, or center=>$pos,, followed by size=>$radius and (optionally) arc=>"[$begin:$end]".

You can specify a polygon with from=>$pos1,to=>$pos2,to=>$pos3,...to=>$posn or with from=>$pos1,rto=>$diff1,rto=>$diff2,...rto=>$diffn.

( front | back | behind ) - draw the object last | first | really-first.
fc <colorspec> - specify fill color
fs <fillstyle> - specify fill style
lw <width> - multiplier on line width

POs for appearance tweaks - bars, boxwidth, isosamples, pointsize, style

bars sets the width and behavior of the tick marks at the ends of error bars. It takes a list containing at most two elements, both of which are optional:

  • A width specifier, which should be a numeric size multiplier times the usual width (which is about one character width in the default font size), or the word fullwidth to make the ticks the same width as their associated boxes in boxplots and histograms.

  • the word "front" or "back" to indicate drawing order in plots that might contain filled rectangles (e.g. boxes, candlesticks, or histograms).

If you pass in the undefined value you get no ticks on errorbars; if you pass in the empty list ref you get default ticks.

boxwidth sets the width of drawn boxes in boxplots, candlesticks, and histograms. It takes a list containing at most two elements:

  • a numeric width

  • one of the words absolute or relative.

Unless you set relative, the numeric width sets the width of boxes in X-axis scientific units (on log scales, this is measured at x=1 and the same width is used throughout the plot plane). If relative is included, the numeric width is taken to be a multiplier on the default width.

isosamples sets isoline density for plotting functions as surfaces. You supply one or two numbers. The first is the number of iso-u lines and the second is the number of iso-v lines. If you only specify one, then the two are taken to be the same. From the gnuplot manual: "An isoline is a curve parameterized by one of the surface parameters while the other surface parameter is fixed. Isolines provide a simple means to display a surface. By fixing the u parameter of surface s(u,v), the iso-u lines of the form c(v) = s(u0,v) are produced, and by fixing the v parameter, the iso-v lines of the form c(u)=s(u,v0) are produced".

pointsize accepts a single number and scales the size of points used in plots.

style provides a great deal of customization for individual plot styles. It is not (yet) fully parsed by PDL::Graphics::Gnuplot; please refer to the Gnuplot manual for details (it is pp. 145ff in the Gnuplot 4.6.1 maual). style accepts a hash ref whose keys are plot styles (such as you would feed to the with curve option), and whose values are list refs containing keywords and other parameters to modify how each plot style should be displayed.

POs for locale/internationalization - locale, decimalsign

locale is used to control date stamp creation. See the gnuplot manual.

decimalsign accepts a character to use in lieu of a "." for the decimalsign. (e.g. in European countries use decimalsign=>',').

globalwith is used as a default plot style if no valid 'with' curve option is present for a given curve.

If set to a nonzero value, timestamp causes a time stamp to be placed on the side of the plot, e.g. for keeping track of drafts.

zero sets the approximation threshold for zero values within gnuplot. Its default is 1e-8.

fontpath sets a font search path for gnuplot. It accepts a collection of file names as a list ref.

POs for advanced Gnuplot tweaks: topcmds, extracmds, bottomcmds, binary, dump, tee

Plotting is carried out by sending a collection of commands to an underlying gnuplot process. In general, the plot options cause "set" commands to be sent, configuring gnuplot to make the plot; these are followed by a "plot" or "splot" command and by any cleanup that is necessary to keep gnuplot in a known state.

Provisions exist for sending commands directly to Gnuplot as part of a plot. You can send commands at the top of the configuration but just under the initial "set terminal" and "set output" commands (with the topcmds option), at the bottom of the configuration and just before the "plot" command (with the extracmds option), or after the plot command (with the bottomcmds option). Each of these plot options takes a list ref, each element of which should be one command line for gnuplot.

Most plotting is done with binary data transfer to Gnuplot; however, due to some bugs in Gnuplot binary handling, certain types of plot data are sent in ASCII. In particular, time series and label data require transmission in ASCII (as of Gnuplot 4.4). You can force ASCII transmission of all but image data by explicitly setting the binary=>0 option.

dump is used for debugging. If true, it writes out the gnuplot commands to STDOUT instead of writing to a gnuplot process. Useful to see what commands would be sent to gnuplot. This is a dry run. Note that if the 'binary' option is given (see below), then this dump will contain binary data. If this binary data should be suppressed from the dump, set dump => 'nobinary'.

tee is used for debugging. If true, writes out the gnuplot commands to STDERR in addition to writing to a gnuplot process. This is not a dry run: data is sent to gnuplot and to the log. Useful for debugging I/O issues. Note that if the 'binary' option is given (see below), then this log will contain binary data. If this binary data should be suppressed from the log, set tee => 'nobinary'.


The curve options describe details of specific curves within a plot. They are in a hash, whose keys are as follows:


Specifies the legend label for this curve


Lets you specify which X and/or Y axes to plot on. Gnuplot supports a main and alternate X and Y axis. You specify them as a packed string with the x and y axes indicated: for example, x1y1 to plot on the main axes, or x1y2 to plot using an alternate Y axis (normally gridded on the right side of the plot).


Specifies the plot style for this curve. The value is passed to gnuplot using its 'with' keyword, so valid values are whatever gnuplot supports. See above ("Plot styles supported") for a list of supported curve styles.

The following curve options in this list modify the plot style further. Not all of them are applicable to all plot styles -- for example, it makes no sense to specify a fill style for with=>lines.

For historical reasons, you can supply the with modifier curve options as a single string in the "with" curve option. That usage is deprecated and will disappear in a future version of PDL::Graphics::Gnuplot.

linetype (abbrev 'lt')

This is a numeric selector from the default collection of line styles. It includes automagic selection of dash style, color, and width from the default set of linetypes for your current output terminal.

dashtype (abbrev 'dt')

This is can be either a numeric type selector (0 for no dashes) or an ARRAY ref containing a list of up to 5 pairs of (dash length, space length). The dashtype curve option is only supported for Gnuplot versions 5.0 and above.

If you don't specify a dashtype curve option, the default behavior matches the behavior of earlier gnuplots: many terminals support a "dashed" terminal/output option, and if you have set that option (with the constructor or with the output method) then lines are uniquely dashed by default. To make a single curve solid, specify dt=0> as a curve option for it; or to make all curves solid, use the constructor or the output method to set the terminal option dashed=0>.

If your gnuplot is older than v5.0, the dashtype curve option is ignored (and causes a warning to be emitted).

linestyle (abbrev 'ls')

This works exactly like linetype above, except that you can modify individual line styles by setting the style line <num> plot option. That is handy for a custom style you might use across several curves either a single plot or several plots.

linewidth (abbrev 'lw')

This is a numeric multiplier on the usual default line width in your current terminal.

linecolor (abbrev 'lc')

This is a color specifier for the color of the line. You can feed in a standard color name (they're listed in the package-global variable @PDL::Graphics::Gnuplot::colornames), a small integer to index the standard linetype colors, the word "variable" to indicate that the line color is a standard linetype color to be drawn from an additional column of data, [rgbcolor=><num>] to specify an RGB color as a 24-bit packed integer, [rgbcolor=>'variable'] to specify an additional column of data containing 24-bit packed integers with RGB color values, [palette=>'frac',<val>] to specify a single fractional position (scaled 0-1) in the current palette, or [palette=>'cb',<val>] to specify a single value in the scaled cbrange.

There is no linecolor=>[palette=>variable] due to Gnuplot's non-orthogonal syntax. To draw line color from the palette, via an additional data column, see the separate "palette" curve option (below).

textcolor (abbrev 'tc')

For plot styles like labels that specify text, this sets the color of the text. It has the same format as linecolor (above).

pointtype (abbrev 'pt')

Selects a point glyph shape from the built-in list for your terminal, for plots that render points as small glyphs (like points and linespoints).

pointsize (abbrev 'ps')

Selects a fractional size for point glyphs, relative to the default size on your terminal, for plots that render points as small glyphs.

fillstyle (abbrev 'fs')

Specify the way that filled regions should be colored, in plots that have fillable areas (like boxes). Unlike linestyle above, fillstyle accepts a full specification rather than an index into a set of predefined styles. You can feed in: 'empty' for no fill; 'transparent solid <density>' for a solid fill with optional <density> from 0.0 to 1.0 (default 1.0); 'transparent pattern <n>' for a pattern fill--plotting multiple datasets causes the pattern to cycle through all available pattern types, starting from pattern <n> (be aware that the default <n>=0 may be equivalent to 'empty'); The 'transparent' portions of the strings are optional, and are only effective on terminals that support transparency. Be aware that the quality of the visual output may depend on terminal type and rendering software.

Any of those fill style specification strings can have a border specification string appended to it. To specify a border, append 'border', and then optionally either 'lt=><type>' or 'lc=><colorspec>' to the string. To specify no border, append 'noborder'.


If you are making a 3D plot and have used the plot option hidden3d to get hidden line removal, you can override that for a particular curve by setting the nohidden3d option to a true value. Only the single curve with nohidden3d set will have its hidden points rendered.


If you are making a contour 3D plot, you can inhibit rendering of contours for a particular curve by setting nocontours to a true value.


If you are making a surface 3D plot, you can inhibit rendering of the surface associated with a particular curve, by setting nosurface to a true value.


Setting palette => 1 causes line color to be drawn from an additional column in the data tuple. This column is always the very last column in the tuple, in case of conflict (e.g. if you set both pointsize=>variable and palette=>1, then the palette column is the last column and the pointsize column is second-to-last).


Specifies how many values represent each data point. Normally you don't need to set this as individual with styles implicitly set a tuple size (which is automatically extended if you specify additional modifiers such as palette that require more data); this option lets you override PDL::Graphics::Gnuplot's parsing in case of irregularity.


Specifies the dimensions of of each column in this curve's tuple. It must be 0, 1, or 2. Normally you don't need to set this for most plots; the main use is to specify that a 2-D data PDL is to be interpreted as a collection of 1-D columns rather than a single 2-D grid (which would be the default in a 3-D plot). For example:

    $r2 = rvals(21,21)**2;
    $w->plot3d( wi=>'lines', xvals($r2), yvals($r2), $r2 );

will produce a grid of values on a paraboloid. To instead plot a collection of lines using the threaded syntax, try

    $w->plot3d( wi=>'lines', cd=>1, xvals($r2), yvals($r2), $r2 );

which will plot 21 separate curves in a threaded manner.


Most of these come directly from Gnuplot commands. See the Gnuplot docs for details.

2D plotting

If we're plotting a piddle $y of y-values to be plotted sequentially (implicit domain), all you need is


If we also have a corresponding $x domain, we can plot $y vs. $x with

  gplot($x, $y);

Simple style control

To change line thickness:

  gplot(with => 'lines',linewidth=>4, $x, $y);
  gplot(with => 'lines', lw=>4, $x, $y);

To change point size and point type:

  gplot(with => 'points',pointtype=>8, $x, $y);
  gplot(with => 'points',pt=>8, $x, $y);


To plot errorbars that show $y +- 1, plotted with an implicit domain

  gplot(with => 'yerrorbars', $y, $y->ones);

Same with an explicit $x domain:

  gplot(with => 'yerrorbars', $x, $y, $y->ones);

Symmetric errorbars on both x and y. $x +- 1, $y +- 2:

  gplot(with => 'xyerrorbars', $x, $y, $x->ones, 2*$y->ones);

To plot asymmetric errorbars that show the range $y-1 to $y+2 (note that here you must specify the actual errorbar-end positions, NOT just their deviations from the center; this is how Gnuplot does it)

  gplot(with => 'yerrorbars', $y, $y - $y->ones, $y + 2*$y->ones);

More multi-value styles

Plotting with variable-size circles (size given in plot units, requires Gnuplot >= 4.4)

  gplot(with => 'circles', $x, $y, $radii);

Plotting with a variably-sized arbitrary point type (size given in multiples of the "default" point size)

  gplot(with => 'points', pointtype=>7, pointsize=>'variable',
        $x, $y, $sizes);

Color-coded points

  gplot(with => 'points', palette=>1,
        $x, $y, $colors);

Variable-size AND color-coded circles. A Gnuplot (4.4.0) bug make it necessary to specify the color range here

  gplot(cbmin => $mincolor, cbmax => $maxcolor,
        with => 'circles', palette=>1,
        $x, $y, $radii, $colors);

3D plotting

General style control works identically for 3D plots as in 2D plots.

To plot a set of 3d points, with a square aspect ratio (squareness requires Gnuplot >= 4.4):

  splot(square => 1, $x, $y, $z);

If $xy is a 2D piddle, we can plot it as a height map on an implicit domain


Complicated 3D plot with fancy styling:

  my $pi    = 3.14159;
  my $theta = zeros(200)->xlinvals(0, 6*$pi);
  my $z     = zeros(200)->xlinvals(0, 5);

  splot(title => 'double helix',

        { with => 'linespoints',
          legend => 'spiral 1' },
        { legend => 'spiral 2' },

        # 2 sets of x, 2 sets of y, single z
        PDL::cat( cos($theta), -cos($theta)),
        PDL::cat( sin($theta), -sin($theta)),

        # pointsize, color
        0.5 + abs(cos($theta)), sin(2*$theta) );

3D plots can be plotted as a heat map.

  splot( extracmds => 'set view 0,0',
         with => 'image',
         $xy );


To send any plot to a file, instead of to the screen, one can simply do

  gplot(hardcopy => 'output.pdf',
        $x, $y);

The hardcopy option is a shorthand for the terminal and output options. The output device is chosen from the file name suffix.

If you want more (any) control over the output options (e.g. page size, font, etc.) then you can specify the output device using the output method or the constructor itself -- or the corresponding plot options in the non-object mode. For example, to generate a PDF of a particular size with a particular font size for the text, one can do

  gplot(terminal => 'pdfcairo solid color font ",10" size 11in,8.5in',
        output   => 'output.pdf',
        $x, $y);

This command is equivalent to the hardcopy shorthand used previously, but the fonts and sizes can be changed.

Using the object oriented mode, you could instead say:

  $w = gpwin();
  $w->plot( $x, $y );
  $w->output( pdfcairo, solid=>1, color=>1,font=>',10',size=>[11,8.5,'in'] );

Many hardcopy output terminals (such as pdf and svg) will not dump their plot to the file unless the file is explicitly closed with a change of output device or a call to reset, restart, or close. This is because those devices support multipage output and also require and end-of-file marker to close the file.

Plotting examples

A simple example

   my $win = gpwin('x11');
   $win->plot( sin(xvals(45)) * 3.14159/10 );

Here we just plot a simple function. The default plot style is a line. Line plots take a 2-tuple (X and Y values). Since we have supplied only one element, plot() understands it to be the Y value (abscissa) of the plot, and supplies value indices as X values -- so we get a plot of just over 2 cycles of the sine wave over an X range across X values from 0 to 44.

A not-so-simple example

   $win = gpwin('x11');
   $pi = 3.14159;
   $win->plot( {with => line}, xvals(10)**2, xvals(10),
               {with => circles}, 2 * xvals(50), 2 * sin(xvals(50) * $pi / 10), xvals(50)/20

This plots sqrt(x) in an interesting way, and overplots some circles of varying size. The line plot accepts a 2-tuple, and we supply both X and Y. The circles plot accepts a 3-tuple: X, Y, and R.

A complicated example:

   $pi    = 3.14159;
   $theta = xvals(201) * 6 * $pi / 200;
   $z     = xvals(201) * 5 / 200;

   gplot( {trid => 1, title => 'double helix',cbr=>[0,1]},
         {with => 'linespoints',
          legend => ['spiral 1','spiral 2'],
         pdl( cos($theta), -cos($theta) ),       # x
         pdl( sin($theta), -sin($theta) ),       # y
         $z,                                     # z
         (0.5 + abs(cos($theta))),               # pointsize
         sin($theta/3),                          # color
         { with=>'points',
         zeroes(6),                         # x
         zeroes(6),                         # y
         xvals(6),                          # z
         xvals(6)+1                         # point size

This is a 3d plot with variable size and color. There are 5 values in the tuple. The first 2 piddles have dimensions (N,2); all the other piddles have a single dimension. The "cdim=>1" specifies that each column of data should be one-dimensional. Thus the PDL threading generates 2 distinct curves, with varying values for x,y and identical values for everything else. To label the curves differently, 2 different sets of curve options are given. Omitting the "cdim" curve option would yield a 201x2 grid with the "linespoints" plotstyle, rather than two separate curves.

In addition to the threaded pair of linespoints curves, there are six variable size points plotted as filled squares, as a secondary curve.

Plot options are passed in in two places: as a leading hash ref, and as a trailing hash ref. Any other hash elements or hash refs must be curve options.

Curves are delimited by non-data arguments. After the initial hash ref, curve options for the first curve (the threaded pair of spirals) are passed in as a second hash ref. The curve's data arguments are ended by the first non-data argument (the hash ref with the curve options for the second curve).



 use PDL::Graphics::Gnuplot;
 $w = gpwin( @options );
 $w->plot( @plot_args );

gpwin is the PDL::Graphics::Gnuplot exported constructor. It is exported by default and is a synonym for "new PDL::Graphics::Gnuplot(...)". If given no arguments, it creates a plot object with the default terminal settings for your gnuplot. You can also give it the name of a Gnuplot terminal type (e.g. 'x11') and some terminal and output options (see "output").


    $w = new PDL::Graphics::Gnuplot;
    $w->plot( @plot_args );
    # Specify plot options alone
    $w = new PDL::Graphics::Gnuplot( {%plot_options} );
    # Specify device and device options (and optional default plot options)
    $w = new PDL::Graphics::Gnuplot( device, %device_options, {%plot_options} );
    $w->plot( @plot_args );

Creates a PDL::Graphics::Gnuplot persistent plot object, and connects it to gnuplot.

For convenience, you can specify the output device and its options right here in the constructor. Because different gnuplot devices accept different options, you must specify a device if you want to specify any device configuration options (such as window size, output file, text mode, or default font).

If you don't specify a device type, then the Gnuplot default device for your system gets used. You can set that with an environment variable (check the Gnuplot documentation).

Gnuplot uses the word "terminal" for output devices; you can see a list of terminals supported by PDL::Graphics::Gnuplot by invoking PDL::Graphics::Gnuplot::terminfo() (for example in the perldl shell).

For convenience, you can provide default plot options here. If the last argument to new() is a trailing hash ref, it is treated as plot options.

After you have created an object, you can change its terminal/output device with the output method, which is useful for (e.g.) throwing up an interactive plot and then sending it to a hardcopy device. See output for a description of terminal options and how to format them.

Normally, the object connects to the command "gnuplot" in your path, using the Alien::Gnuplot module. If you need to specify a binary other than this default, check the Alien::Gnuplot documentation.

  my $plot = PDL::Graphics::Gnuplot->new({title => 'Object-oriented plot'});
  $plot->plot( legend => 'curve', sequence(5) );


    $window->output( $device );
    $window->output( $device, %device_options );
    $window->output( $device, %device_options, {plot_options} );
    $window->output( %device_options, {plot_options} );
    $window->output( %device_options );

Sets the output device and options for a Gnuplot object. If you omit the $device name, then you get the gnuplot default device (generally x11, wxt, or aqua, depending on platform).

You can control the output device of a PDL::Graphics::Gnuplot object on the fly. That is useful, for example, to replot several versions of the same plot to different output devices (interactive and hardcopy).

Gnuplot interprets terminal options differently per device. PDL::Graphics::Gnuplot attempts to interpret some of the more common ones in a common way. In particular:


Most drivers support a "size" option to specify the size of the output plotting surface. The format is [$width, $height, $unit]; the trailing unit string is optional but recommended, since the default unit of length changes from device to device.

The unit string can be in, cm, mm, px, char, or pt. Pixels are taken to be 1 point in size (72 pixels per inch) and dimensions are computed accordingly. Characters are taken to be 12 point in size (6 per inch).


This option actually sets the object's "output" option for most terminal devices; that changes the file to which the plot will be written. Some devices, notably X11 and Aqua, don't make proper use of "output"; for those devices, specifying "output" in the object constructor actually sets the appropriate terminal option (e.g. "window" in the X11 terminal). This is described as a "plot option" in the Gnuplot manual, but it is treated as a setup variable and parsed with the setup/terminal options here in the constructor.

If you don't specify an output device, plots will go to sequentially-numbered files of the form Plot-<n>.<suf> in your current working directory. In that case, PDL::Graphics::Gnuplot will report (on STDERR) where the plot ended up.


This is a flag that indicates whether to enable Gnuplot's enhanced text processing (e.g. for superscripts and subscripts). Set it to a false value for plain text, to a true value for enhanced text (which includes LaTeX-like markup for super/sub scripts and fonts).

For a brief description of the terminal options that any one device supports, you can run PDL::Graphics::Gnuplot::terminfo().

As with plot options, terminal options can be abbreviated to the shortest unique string -- so (e.g.) "size" can generally be abbreviated "si" and "monochrome" can be abbreviated "mono" or "mo".



Close gnuplot process (actually just a synonym for restart)

Some of the gnuplot terminals (e.g. pdf) don't write out a file promptly. The close method closes the associated gnuplot subprocess, forcing the file to be written out. It is implemented as a simple restart operation.

The object preserves the plot state, so replot and similar methods still work with the new subprocess.



Restart the gnuplot backend for a plot object

Occasionally the gnuplot backend can get into an unknown state. restart kills the gnuplot backend and starts a new one, preserving state in the object. (i.e. replot and similar functions work even with the new subprocess).

Called with no arguments, restart applies to the global plot object.



Clear state from the gnuplot backend

Clears all plot option state from the underlying object. All plot options except "terminal", "termoptions", "output", and "multiplot" are cleared. This is similar to the "reset" command supported by gnuplot itself, and in fact it also causes a "reset" to be sent to gnuplot.


  $w = new PDL::Graphics::Gnuplot();
  $w->options( globalwith=>'lines' );
  print %{$w->options()};

Set/get persistent plot options for a plot object

The options method parses plot options into a gnuplot object on a cumulative basis, and returns the resultant options hash.

If called as a sub rather than a method, options() changes the global gnuplot object.


Plot method exported by default (synonym for "PDL::Graphics::Gnuplot::plot")


This is the main plotting routine in PDL::Graphics::Gnuplot.

Each plot() call creates a new plot from whole cloth, either creating or overwriting the output for that device.

If you want to add features to an existing plot, use replot.

plot() understands the PDL bad value mechanism. Bad values are omitted from the plot.

 $w->plot({temp_plot_options},                 # optional
      curve_options, data, data, ... ,      # curve_options are optional for the first plot
      curve_options, data, data, ... ,

Most of the arguments are optional.

All of the extensive array of gnuplot plot styles are supported, including images and 3-D plots.

 use PDL::Graphics::Gnuplot qw(plot);
 my $x = sequence(101) - 50;

See main POD for PDL::Graphics::Gnuplot for details.

You can pass plot options into plot as either a leading or trailing hash ref, or both. If you pass both, the trailing hash ref is parsed last and overrides the leading hash.

For debugging and curiosity purposes, the last plot command issued to gnuplot is maintained in a package global: $PDL::Graphics::Gnuplot::last_plotcmd, and also in each object as the {last_plotcmd} field.


Replot the last plot (possibly with new arguments).

replot is similar to gnuplot's "replot" command - it allows you to regenerate the last plot made with this object. You can change the plot by adding new elements to it, modifying options, or even (with the "device" method) changing the output device. replot takes the same arguments as plot.

If you give no arguments at all (or only a plot object) then the plot is simply redrawn. If you give plot arguments, they are added to the new plot exactly as if you'd included them in the original plot element list, and maintained for subsequent replots.

(Compare to 'markup').


Add ephemeral markup to the last plot.

markup works exactly the same as replot, except that any new arguments are not added to the replot list - so you can add temporary markup to a plot and regenerate the plot later without it.


Generate 3D plots. Synonym for plot(trid => 1, ...)


Generate 3D plots. Synonym for plot(trid => 1, ...)


Generates plots with lines, by default. Shorthand for plot(globalwith => 'lines', ...)


Generates plots with points, by default. Shorthand for plot(globalwith => 'points', ...)


Displays an image (either greyscale or RGB). Shorthand for plot(globalwith => 'image', ...)


Synonym for "image", for people who grew up with PDL::Graphics::PGPLOT and can't remember the closing 'e'


Displays a FITS image. Synonym for plot(globalwith => 'fits', ...).


 $a = (xvals(101)/100) * 6 * 3.14159/180;
 $b = sin($a);

 $w->plot({title=>"lines"}, with=>"lines", $a,$b);
 $w->plot({title=>"image"}, with=>"image", $a->(*1) * $b );

Plot multiple plots into a single page of output.

The multiplot method enables multiplot mode in gnuplot, which permits multiple plots on a single pane. Plots can be lain out in a grid, or can be lain out freeform using the size and origin plot options for each of the individual plots.

It is not possible to change the terminal or output device when in multiplot mode; if you try to do that, by setting one of those plot options, PDL::Graphics::Gnuplot will throw an error.

The options hash will accept:

layout - define a regular grid of plots to multiplot

layout should be followed by an ARRAY ref that contains at least number of columns ("NX") followed by number of rows ("NY). After that, you may include any of the "rowsfirst", "columnsfirst", "downwards", or "upwards" keywords to specify traversal order through the grid. Only the first letter is examined, so (e.g.) "down" or even "dog" works the same as "downwards".

title - define a title for the entire page

title should be followed by a single scalar containing the title string.

scale - make gridded plots larger or smaller than their allocated space

scale takes either a scalar or a list ref containing one or two values. If only one value is supplied, it is a general scale factor of each plot in the grid. If two values are supplied, the first is an X stretch factor for each plot in the grid, and the second is a Y stretch factor for each plot in the grid.

offset - offset each plot from its grid origin

offset takes a list ref containing two values, that control placement of each plot within the grid.



Ends a multiplot block (i.e. a block of plots that are meant to render to a single page).


  ($x,$y,$char,$modstring) = $w->read_mouse($message);
  $hash = $w->read_mouse($message);

Get a mouse click or keystroke from the active interactive plot window.

For interactive devices (e.g. x11, wxt, aqua), read_mouse lets you accept a keystroke or mouse button input from the gnuplot window. In list context, it returns four arguments containing the reported X, Y, keystroke character, and modifiers packed in a string. In scalar context, it returns a hash ref containing those things.

read_mouse blocks execution for input, but responds gracefully to interrupts.


  $points = $w->read_polygon(%opt)

Read in a polygon by accepting mouse clicks. The polygon is returned as a 2xN PDL of ($x,$y) values in scientific units. Acceptable options are:

message - what to print before collecting points

There are some printf-style escapes for the prompt:

* %c - expands to "an open" or "a closed"

* %n - number of points currently in the polygon

* %N - number of points expected for the polygon

* %k - list of all keys accepted

* %% - %

prompt - what to print to prompt the user for the next point

prompt uses the same escapes as message.

n_points - number of points to accept (or 0 for indefinite)

With 0 value, points are accepted until the user presses 'q' or 'ESC' on the keyboard with focus on the graph. With other value, points are accepted until that happens *or* until the number of points is at least n_points.

actions - hash of callback code refs indexed by character for action

You can optionally call a callback routine when any particular character is pressed. The actions table is a hash ref whose keys are characters and whose values are either code refs (to be called on the associated keypress) or array refs containing a short description string followed by a code ref. Non-printable characters (e.g. ESC, BS, DEL) are accessed via a hash followed by a three digit decimal ASCII code -- e.g. "#127" for DEL. Button events are indexed with the strings "BUTTON1", "BUTTON2", and "BUTTON3", and modifications must be entered as well for shift, control, and

The code ref receives the arguments ($obj, $c, $poly,$x,$y,$mods), where:

$obj is the plot object
$c is the character (or "BUTTONn" string),
$poly is a scalar ref; $$poly is the current polygon before the action,
$x and $y are the current scientific coordinates, and
$mods is the modifier string.

You can't override the 'q' or '#027' (ESC) callbacks. You *can* override the BUTTON1 and DEL callbacks, potentially preventing the user from entering points at all! You should do that with caution.

closed - (default false): generate a closed polygon

This works by duplicating the initial point at the end of the point list.

markup - (default 'linespoints'): style to use to render the polygon on the fly

If this is set to a true value, it should be a valid 'with' specifier (curve option). The routine will call markup after each click.


    use PDL::Graphics::Gnuplot qw/terminfo/;
    terminfo();        # print info about all known terminals
    terminfo 'aqua';   # print info about the aqua terminal

    $w = gpwin();

Print out information about gnuplot terminals and their custom option syntax.

The "terminfo" routine is a reference tool to describe the Gnuplot terminal types and the options they accept. It's mainly useful in interactive sessions. It outputs information directly to the terminal.


Everything should work on all platforms that support Gnuplot and Perl. Currently, MacOS, Fedora and Debian Linux, Cygwin, and Microsoft Windows (under both Active State Strawberry Perl) have been tested to work, although the interprocess control link is not as reliable under Microsoft Windows as under POSIX systems. Please report successes or failures on other platforms to the authors. A transcript of a failed run with {tee => 1} would be most helpful.




Craig DeForest, <craig@deforest.org> and Dima Kogan, <dima@secretsauce.net>


some plot and curve options need better parsing:
- labels need attention (plot option labels)

They need to be handled as hashes, not just as array refs. Also, they don't seem to be working with timestamps. Further, deeply nested options (e.g. "at" for labels) need attention.

- new plot styles

The "boxplot" plot style (new to gnuplot 4.6?) requires a different using syntax and will require some hacking to support.


Copyright 2011-2013 Craig DeForest and Dima Kogan

This program is free software; you can redistribute it and/or modify it under the terms of either: the GNU General Public License as published by the Free Software Foundation; or the Perl Artistic License included with the Perl language.

See http://dev.perl.org/licenses/ for more information.