If method "rchart_option::set_tooltip" is used for radar charts the third parameter must be provided and must be set to "true".
<?php

include_once "environment.php";


$template = "default.php";
$width = "500";
$height = "400";
$draw_option = "grow();";

$data = array( array(4,8,5,2,3),array(9,5,6,3,5));
$labels = array('Marvin', 'Barry', 'Gary','Dave','Paul');

$chart = new rgraph_chart("cvs", $data, "Radar");

$options = new rgraph_options("default.ini");
$options->set_option("title", "An animated Radar Chart with interactive Key");
$options->set_option("labels",$labels);
$options->set_option("titleY",15);
$options->setColorOpacity(0.6);
$options->set_option("key", array("Winners", "Losses"));
$options->set_option("keyPosition", "margin");
$options->set_option("keyPositionY", 360);
$options->set_option("keyInteractive", true);
$options->set_tooltip($data, "#label#: #val# #key#", true);

$chart->set_options($options);
$rgraph_json = $chart->toString();

$chart_script = "";
$event_script = "";

$canvas_style = "background-repeat: no-repeat;
 background-image: url(images/pv_system.jpg); background-size: 100% 100%;";

include_once ($templates . $template);
?>