def to_JSON(self):
        """Dumps object fields into a JSON formatted string

        :returns: the JSON string

        """
        return json.dumps({'id': self.id,
                           'external_id': self.external_id,
                           'name': self.name,
                           'created_at': timeformatutils.to_ISO8601(self.created_at),
                           'updated_at': timeformatutils.to_ISO8601(self.updated_at),
                           'lat': self.lat,
                           'lon': self.lon,
                           'alt': self.alt if self.alt is not None else 'None',
                           'rank': self.rank})