By default the start angle (angle=0) is located at the 3'a clock position. By calling the method Graph::Set90AndMargin() it is possible to rotate the graph so that the 0-angle position is at the 6'a clock position (straight down). This is mostly used for full 360 degree graphs.

By default the angle is counted counter-clockwise as is custom in most application of polar plots. However, it is also possible to have the angles counted clockwise. This is done by calling the method Graph::SetClockwise().

In the following two examples we show a full 360 degree polar plots with clockwise ordering in both a standard configuration and also as a 90 degrees rotated graph.

Figure 16.45. Clockwise polar graph (polarclockex1.php)

Figure 16.46. Rotated clockwise polar graph (polarclockex2.php)

The principle is exactly the same as for line plots but instead of an x-y coordinate each point is represented by a angle and a radius to specify its position. The data is given in the format

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$data = array(angle1, radius1, angle2, radius2, ...)

Creation of a single polar plot follows the now familiar structure as shown in the following code snippet

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<?php
...
// Setup the graph
$graph = new PolarGraph($width,$height);
 
// Set a logarithmic scale with 100 as the maximum value, i.e. 10^2
$graph->SetScale('log',100);
 
// Use a full 360 degree polar graph
$graph->SetType(POLAR_360);
 
// Create a plot with marks
$polarplot = new PolarPlot($data);
$polarplot->mark->SetType(MARK_SQUARE);
 
// Add it to the graph
$graph->Add($polarplot);
...
?>

Adding multiple polar plots follows the same pattern. Each polar plot is created as an instance of class PolarPlot and then added to the graph.

In exactly the same way as for line graphs it is possible to add plot marks in radar plots. The mark property is accessed through the instance variable

(All available plot marks are listed in Appendix E. Available plot marks)

For example to add a square marker (with the default color) the following line must be added

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$polarplot->mark->SetType(MARK_SQUARE);

In Figure 16.47. Adding plot marks to a polar graph (polarex7-1.php) we show a polar graph with added plot-marks. In addition we have added a gradient background.

Figure 16.47. Adding plot marks to a polar graph (polarex7-1.php)

(See Chapter 10. Using CSIM (Client side image maps) for a full description on the usage of CSIM together with the library)

If markers are shown for the polar plot (by setting the mark property of the plot) each marker can be a hot spot in a client side image map. The target URL are as usual specified with the SetCSIMTargets() as the following short code snippet shows

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<?php
// Start by specifying the proper URL targets
$targets  = array( "#1" , "#2" , ....... );
$polarplot = new PolarPlot( $data );
$polarplot->mark->SetType( MARK_SQUARE );
$polarplot->SetCSIMTargets( targets );
$graph->Add( $polarplot );
$graph->StrokeCSIM(); 
?>

The radius axis can be shown in either a linear or logarithmic scale. This is controlled by a call to

The two examples below show the same plot in either linear or logarithmic scale for the radius

Figure 16.48. Linear scale for radius (polarex3-lin.php)

Figure 16.49. Logarithmic scale for radius (polarex3.php)

Please note that the maximum values of the scales are different.

By default the scale will be auto scaled depending on the data. It is also possible to specify a manual scale by supplying an extra argument to the SetScale() method.

The only difference from the manual scaling with the standard x-y-graphs is that for polar graph only the maximum value is manually specified. The minimum will always be 0 for the linear scale and a scaled value of 10 (i.e 1, 0.1, 0.001 and so on) for the logarithmic scale.

The graph allows several formatting option for the grid lines. For polar plots there are two types of grid lines, the angle and the radius grid lines.

Grid lines format is controlled by

The two example below shows a logarithmic plot with either just major grid lines or both minor and major grid lines.

Figure 16.50. Logarithmic scale with only major grid lines (polarex4.php)

Figure 16.51. Logarithmic scale with both major and minor grid lines (polarex5.php)

It is possible to individually specify different fonts and colors for the angle and the radius labels.

The following example specifies different color for the labels. it also shows how to add both a radial axis title as well as a tabbed title. In this example we have also chosen not to show the frame around the edge of the plot.

Figure 16.52. Different colors for labels, specifying both a tabbed title as well as a axis title (polarex9.php)