Here are some handy routines for rotation and translation of polygons.  Scaling could be added easily as well.

<?php
function translate_point(&$x,&$y,$angle,$about_x,$about_y,$shift_x,$shift_y)
{
    $x -= $about_x;
    $y -= $about_y;
    $angle = ($angle / 180) * M_PI;
/* math:
[x2,y2] = [x,  *  [[cos(a),-sin(a)],
           y]      [sin(a),cos(a)]]
==>
x = x * cos(a) + y*sin(a) 
y = x*-sin(a) + y*cos(a)
*/

    $new_x = $x * cos($angle) - $y * sin($angle);
    $new_y = $x * sin($angle) + $y * cos($angle);
    $x = $new_x+ $about_x + $shift_x ;
    $y = $new_y + $about_y + $shift_y;
}

function translate_poly($point_array, $angle, $about_x, $about_y,$shift_x,$shift_y)
{
    $translated_poly = Array();
    while(count($point_array) > 1)
    {
        $temp_x = array_shift($point_array);
        $temp_y = array_shift($point_array);
        translate_point($temp_x, $temp_y, $angle, $about_x, $about_y,$shift_x, $shift_y);
        array_push($translated_poly, $temp_x);
        array_push($translated_poly, $temp_y);
    }
    return $translated_poly;
}
?>