public function addPolyCoordinate($x, $y)
    {
        if ($this->type !== 'poly') {
            throw OverlayException::invalidMarkerShapeAddPolyCoordinateCall();
        }

        if (!is_numeric($x) || !is_numeric($y)) {
            throw OverlayException::invalidMarkerShapePolyCoordinate();
        }

        $this->coordinates[] = $x;
        $this->coordinates[] = $y;
    }