code: def add_geo(self, geo_location):
          
          if not geo_location.xpath('latitude') and geo_location.xpath('longitude'):
              raise Exception("Invalid geo-location %s" % etree.tostring(geo_location))
          if _xpath_or_none(geo_location, 'horizontal-datum/text()') not in ('wgs84', None):
              logger.warning("Unsupported horizontal-datum in %s" % etree.tostring(geo_location))
              return
          point = (
              float(_xpath_or_none(geo_location, 'longitude/text()')) / 1000000,
              float(_xpath_or_none(geo_location, 'latitude/text()')) / 1000000
          )
          self.points.add(point)
docs: Saves a <geo-location> Element, to be incoporated into the Open511
          geometry field.