public function addPolygon($points)
    {
        $pointCount = count($points);

        $this->dataString .= 'M'. 
            number_format($points[0]->x, 2, '.', '') .' '. 
            number_format($points[0]->y, 2, '.', '');

        for ($i = 1; $i < $pointCount; $i++) {
            $this->dataString .= 'L'. 
                number_format($points[$i]->x, 2, '.', '') .' '. 
                number_format($points[$i]->y, 2, '.', '');
        }

        $this->dataString .= 'Z';
    }