public function getRotation()
    {
        if ($this->rotation === null) {
            $match = array();
            preg_match(self::$REGEX_ROTATION, $this->output, $match);
            $this->rotation = (array_key_exists(1, $match)) ? intval(trim($match[1])) : 0;
        }
        return $this->rotation;
    }