Dean Arnold


DBD::Chart::Plot - Graph/chart Plotting engine for DBD::Chart


    use DBD::Chart::Plot;

    my $img = DBD::Chart::Plot->new();
    my $anotherImg = DBD::Chart::Plot->new($image_width, $image_height);

    $img->setPoints(\@xdataset, \@ydataset, 'blue line nopoints');

    $img->setOptions (
        horizMargin => 75,
        vertMargin => 100,
        title => 'My Graph Title',
        xAxisLabel => 'my X label',
        yAxisLabel => 'my Y label' );

    print $img->plot;


DBD::Chart::Plot creates images of various types of graphs for 2 or 3 dimensional data. Unlike GD::Graph, the input data sets do not need to be uniformly distributed in the domain (X-axis), and may be either numeric, temporal, or symbolic.

DBD::Chart::Plot supports the following:

- multiple data set plots
- line graphs, areagraphs, scatter graphs, linegraphs w/ points, candlestick graphs, barcharts (2-D, 3-D, and 3-axis), histograms, piecharts, box & whisker charts (aka boxcharts), and Gantt charts
- optional iconic barcharts or datapoints
- a wide selection of colors, and point shapes
- optional horizontal and/or vertical gridlines
- optional legend
- auto-sizing of axes based in input dataset ranges
- optional symbolic and temproal (i.e., non-numeric) domain values
- automatic sorting of numeric and temporal input datasets to assure proper order of plotting
- optional X, Y, and Z axis labels
- optional X and/or Y logarithmic scaling
- optional title
- optional adjustment of horizontal and vertical margins
- optional HTML or Perl imagemap generation
- composite images from multiple graphs
- user programmable colors

PREREQUISITES module minimum version 1.26 (available on CPAN) requires additional libraries:



Create an image object: new()

    use DBD::Chart::Plot;

    my $img = DBD::Chart::Plot->new;
    my $img = DBD::Chart::Plot->new ( $image_width, $image_height );
    my $img = DBD::Chart::Plot->new ( $image_width, $image_height, \%colormap );
    my $anotherImg = new DBD::Chart::Plot;

Creates an empty image. If image size is not specified, the default is 400 x 300 pixels.

Graph-wide options: setOptions()

    $img->setOptions (_title => 'My Graph Title',
        xAxisLabel => 'my X label',
        yAxisLabel => 'my Y label',
        xLog => 0,
        yLog => 0,
        horizMargin => $numHorPixels,
        vertMargin => $numvertPixels,
        horizGrid => 1,
        vertGrid => 1,
        showValues => 1,
        legend => \@plotnames,
        genMap => 'a_valid_HTML_anchor_name',
        mapURL => '',
        icon => [ 'redstar.png', 'bluestar.png' ]
        symDomain => 0

As many (or few) of the options may be specified as desired.

width, height

The width and height of the image in pixels. Default is 400 and 300, respectively.

genMap, mapType, mapURL, mapScript

Control generation of imagemaps. When genMap is set to a legal HTML anchor name, an image map of the specified type is created for the image. The default type is 'HTML' if no mapType is specified. Legal types are 'HTML' and 'PERL'.

If mapType is 'PERL', then Perl script compatible text is generated representing an array ref of hashrefs containing the following attributes:

plotnum => the plot number to which this hashref applies (to support multi-range graphs), starting at zero.

x => the domain value for the plot element

y => the range value for the plot element

z => the Z axis value for 3-axis bar charts, if any

shape => the shape of the hotspot area of the plot element, same as for HTML: 'RECT', 'CIRCLE', 'POLY'

coordinates => an arrayref of the (x,y) pixel coordinates of the hotspot area to be mapped; for CIRCLE shape, its (x-center, y-center, radius), for RECT, its (upper-left corner x, upper-left corner y, lower-right corner x, lower-right corner y), and for POLY its the set of vertices (x,y)'s.

If the mapType is 'HTML', then either the mapURL or mapScript (or both) can be specified. mapURL specifies a legal URL string, e.g., '', which will be added to the AREA tags generated for each mapped plot element. mapScript specifies any legal HTML scripting tag, e.g., 'ONCLICK="alert('Got X=:X, Y=:Y')"' to be added to each generated AREA tag.

For both mapURL and mapScript, special variables :PLOTNUM, :X, :Y, :Z can be specified which are replaced by the following values when the imagemap is generated.

Refer to the IMAGEMAP description at for details.

horizMargin, vertMargin

Sets the number of pixels around the actual plot area.

xAxisLabel, yAxisLabel, zAxisLabel

Sets the label strings for each axis.

xLog, yLog

When set to a non-zero value, causes the associated axis to be rendered in log10 format. Z axis plots are currently only symbolic, so no zLog is supported.


Sets a title string to be rendered at the bottom center of the image in bold text.


Sets a string to be rendered in tiny font at the lower right corner of the image, e.g., 'Copyright(C) 2001, Presicient Corp.'.


Set to an array ref of domain names to be displayed in a legend for the various plots. The legend is displayed below the chart, left justified and placed above the chart title string. The legend for each plot is printed in the same color as the plot. If a point shape or icon has been specified for a plot, then the point shape is printed with the label; otherwise, a small line segment is printed with the label. Due to space limitations, the number of datasets plotted should be limited to 8 or less.


When set to a non-zero value, causes the data points for each plotted element to be displayed next to hte plot point.

horizGrid, vertGrid

Causes grid lines to be drawn completely across the plot area.


When set to a non-zero value, causes the X axis tick labels to be rendered vertically.


When set to a non-zero value, forces the (0,0) data point into the graph. Normally, DBD::Chart::Plot will heuristically clip away from the origin is the plot never crosses the origin.


Sets the background color of the image. Default is white.


When set to a non-zero value for barcharts, causes the bars to be rendered in a 3-D effect.


Set to an arrayref of image filenames. The images will be used to plot iconic barcharts or individual plot points, if the 'icon' shape is specified in the property string supplied to the setPoints() function (defined below). The array must match 1-to-1 with the number of plots in the image; icons and predefined point shapes can be mixed in the same image by setting the icon arrayref entry to undef for plots using predefined shapes in the properties string.


When set to a non-zero value, causes the domain to be treated as discrete symbolic values which are evenly distributed over the X-axis. Numeric domains are plotted as scaled values in the image.


When set to a valid format string, the domain data points are treated as associated temporal values (e.g., date, time, timestamp, interval). The values supplied by setPoints will be strings of the specified format (e.g., 'YYYY-MM-DD'), but will be converted to numeric time values for purposes of plotting, so the domain is treated as continuous numeric data, rather than discrete symbolic. Note that for barcharts, histograms, candlesticks, or piecharts, temporal domains are treated as symbolic for plotting purposes, but are sorted as numeric values.


When set to a valid format string, the range data points are treated as associated temporal values (e.g., date, time, timestamp, interval). The values supplied by setPoints will be strings of the specified format (e.g., 'YYYY-MM-DD'), but will be converted to numeric time values for purposes of plotting, so the range is treated as continuous numeric data.


Sets the color of the axis lines and ticks. Default is black.


Sets the color used to render text in the image. Default is black.


Sets the font used to render text in the image. Default is default GD fonts (gdMedium, gdSmall, etc.).

Specifies the name of an image file to be drawn into the background of the image. The logo image is centered in the plot image, and will be clipped if the logo size exceeds the defined width or height of the plot image.

By default, the graph will be centered within the image, with 50 pixel margin around the graph border. You can obtain more space for titles or labels by increasing the image size or increasing the margin values.

Establish data points: setPoints()

    $img->setPoints(\@xdata, \@ydata);
    $img->setPoints(\@xdata, \@ydata, 'blue line');
    $img->setPoints(\@xdata, \@ymindata, \@ymaxdata, 'blue points');
    $img->setPoints(\@xdata, \@ydata, \@zdata, 'blue bar zaxis');

Copies the input array values for later plotting. May be called repeatedly to establish multiple plots in a single graph. Returns a positive integer on success and undef on failure. The global graph properties should be set (via setOptions()) prior to setting the data points. The error() method can be used to retrieve an error message. X-axis values may be non-numeric, in which case the set of domain values is uniformly distributed along the X-axis. Numeric X-axis data will be properly scaled, including logarithmic scaling is requested.

If two sets of range data (ymindata and ymaxdata in the example above) are supplied, and the properties string does not specify a 3-axis barchart, a candlestick graph is rendered, in which case the domain data is assumed non-numeric and is uniformly distributed, the first range data array is used as the bottom value, and the second range data array is used as the top value of each candlestick. Pointshapes may be specified, in which case the top and bottom of each stick will be capped with the specified pointshape. The range and/or domain axis may be logarithmically scaled. If value display is requested, the range value of both the top and bottom of each stick will be printed above and below the stick, respectively.

Plot properties: Properties of each dataset plot can be set with an optional string as the third argument. Properties are separated by spaces. The following properties may be set on a per-plot basis (defaults in capitals):

    -----     ---------  -----------   ----------
        BLACK       LINE        POINTS     FILLCIRCLE
        white      noline      nopoints    opencircle
        lgray       fill                   fillsquare
        gray        bar                    opensquare
        dgray       pie                    filldiamond
        lblue       box                    opendiamond
        blue       zaxis                   horizcross
        dblue      histo                   diagcross
        gold                               icon
        lyellow                            dot

E.g., if you want a red scatter plot (red dots but no lines) with filled diamonds, you could specify

    $p->setPoints (\@xdata, \@ydata, 'Points Noline Red filldiamond');

Specifying icon for the pointshape requires setting the icon object attribute to a list of compatible image filenames (as an arrayref, see below). In that case, the icon images are displayed centered on the associated plotpoints. For 2-D barcharts, a stack of the icon is used to display the bars, including a proportionally clipped icon image to cap the bar if needed.

Draw the image: plot()


Draws the image and returns it as a string. To save the image to a file:

    open (WR,'>plot.png') or die ("Failed to write file: $!");
    binmode WR;            # for DOSish platforms
    print WR $img->plot();
    close WR;

To return the graph to a browser via HTTP:

    print "Content-type: image/png\n\n";
    print  $img->plot();

The range of values on each axis is automatically computed to optimize the data placement in the largest possible area of the image. As a result, the origin (0, 0) axes may be omitted if none of the datasets cross them at any point. Instead, the axes will be drawn on the left and bottom borders using the value ranges that appropriately fit the dataset(s).

Fetch the imagemap: getMap()


Returns the imagemap for the chart. If no mapType was set, or if mapType was set to HTML. the returned value is a valid <MAP...><AREA...></MAP> HTML string. If mapType was set to 'Perl', a Perl-compatible arrayref declaration string is returned.

The resulting imagemap will be applied as follows:

2 axis 2-D Barcharts and Histograms

Each bar is mapped individually.


Each wedge is mapped. The CGI parameter values are used slightly differently than described above:


3-D Barcharts (either 2 or 3 axis)

The top face of each bar is mapped. The Z CGI parameter will be empty for 2 axis barcharts.

3-D Histograms (either 2 or 3 axis)

The right face of each bar is mapped. The Z CGI parameter will be empty for 2 axis barcharts.

Line, point, area graphs

A 4 pixel diameter circle around each datapoint is mapped.

Candlestick graphs

A 4 pixel diameter circle around both the top and bottom datapoints of each stick are mapped.


The area of the box is mapped, and 4-pixel diameter circles are mapped at the end of each extreme whisker.

Gantt Charts

The area of each bar in the chart is mapped.


programmable fonts
symbolic ranges for scatter graphs
axis labels for 3-D charts
SVG support


Copyright (c) 2001 by Presicient Corporation. (

You may distribute this module under the terms of the Artistic License, as specified in the Perl README file.


GD, DBD::Chart. (All available on CPAN).

7 POD Errors

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