def get_abs_url(self, rel_url):
        """
        Create an absolute url from a relative one.

        >>> url_formatter = URLFormatter("example.com", 80)
        >>> url_formatter.get_abs_url("kml_master.kml")
        'http://example.com:80/kml_master.kml'
        """
        rel_url = rel_url.lstrip("/")
        return "{}://{}:{}/{}".format(self.url_scheme, self.host, self.port, rel_url)