Adam Kennedy


Chart::Math::Axis - Implements an algorithm to find good values for chart axis


  # Create a new Axis
  my $axis = Chart::Math::Axis->new;
  # Provide is some data to calculate on
  $axis->add_data( @dataset );
  # Get the values for the axis
  print "Top of axis: "     . $axis->top           . "\n";
  print "Bottom of axis: "  . $axis->bottom        . "\n";
  print "Tick interval: "   . $axis->interval_size . "\n";
  print "Number of ticks: " . $axis->ticks         . "\n";
  # Apply the axis directly to a GD::Graph.
  $axis->apply_to( $graph );


Chart::Math::Axis implements in a generic way an algorithm for finding a set of ideal values for an axis. That is, for any given set of data, what should the top and bottom of the axis scale be, and what should the interval between the ticks be.

The terms top and bottom are used throughout this module, as it's primary use is for determining the Y axis. For calculating the X axis, you should think of 'top' as 'right', and 'bottom' as 'left'.



  my $null = Chart::Math::Axis->new;
  my $full = Chart::Math::Axis->new( @dataset );

The new method creates a new Chart::Math::Axis object. Any arguments passed to the constructor are used as dataset values. Whenever the object has some values on which to work, it will calculate the axis. If the object is created with no values, most methods will return undef.


Returns the maximum value in the dataset.


Returns the minimum value in the dataset.


The top method returns the value that should be the top of the axis.


The bottom method returns the value that should be the bottom of the axis.


Although Chart::Math::Axis can work out scale and intervals, it doesn't know how many pixels you might need, how big labels etc are, so it can determine the tick density you are going to need. The maximum_intervals method returns the current value for the maximum number of ticks the object is allowed to have.

To change this value, see the set_maximum_intervals method. The default for the maximum number of intervals is 10.


The interval_size method returns the interval size in dataset terms.


The ticks method returns the number of intervals that the top/bottom/size values will result in.


  $self->add_data( @dataset );

The add_data method allows you to provide data that the object should be aware of when calculating the axis. In fact, you can add additional data at any time, and the axis will be updated as needed.


  $self->set_maximum_intervals( $intervals );

The set_maximum_intervals method takes an argument and uses it as the maximum number of ticks the axis is allowed to have.


If you have a dataset something like ( 10, 11, 12 ) the bottom of the axis will probably be somewhere around 9 or 8. That is, it won't show the zero axis. If you want to force the axis to include zero, use this method to do so.


  $self->apply_to( $gd_graph_object )

The apply_to method is intended to provide a series of shortcuts for automatically applying an axis to a graph of a know type. At the present, this will change only the Y axis of a GD::Graph object. This method is considered experimental. If in doubt, extract and set the graph values yourself.


Bugs should be reported via the CPAN bug tracker

For other issues, or commercial enhancement or support, contact the author.


Adam Kennedy <>




Copyright 2002 - 2011 Adam Kennedy.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

The full text of the license can be found in the LICENSE file included with this module.