We normally would like something more meaningful as description of each axis than it's number. Specifying the titles are accomplished through the use of the method SetTitles() of the graph. Let's say that each axis corresponds to a month. We could then use the code
$titles = $gDateLocale ->GetShortMonth ();
As you can see the way radar plot is constructed will assign the titles (and plot points) in a counter-clockwise direction. If you want them in clock-wise order you will have to inverse your input data array as well as the title array.
To specify a legend you (as with the other plot) make use of the SetLegend(); method on each radar plot.