Updates AGeoDataset to support DEM instantiation using ISD or state for CSM

        self.dem = dem

        self.dem_type = dem_type

    def _parse_radii_from_csm(self, input):

        with open(input, 'r') as stream:

            line = stream.readline()

        if line.startswith('{'):

            return self._parse_radii_from_isd(self, input)

        else:

            return self._parse_radii_from_state(self, input)

    def _parse_radii_from_state(self, state):

        with open(state, 'r') as stream:

            stream.readline()

            state = json.load(stream)

        semimajor = state['m_majorAxis']

        semiminor = state['m_minorAxis']

        return semimajor, semiminor

    def _parse_radii_from_isd(self, isd):

        with open(isd, 'r') as stream:

            isd = json.load(stream)

        if not hasattr(self, '_sensormodel'):

            if self.sensortype == 'csm':

                cam_path = self.file_name.replace('.cub', '.json')

                self._make_dem_from_isd(cam_path)

                self._make_dem_from_csm(cam_path)

            else:

                cam_path = self.file_name

                self._make_dem_from_isis()