The :class:`GeodeticCRS` on which this projection is based.

def base_geodetic_crs(self):
        """The :class:`GeodeticCRS` on which this projection is based."""
        base = self.element.find(GML_NS + 'baseGeodeticCRS')
        href = base.attrib[XLINK_NS + 'href']
        return get(href)