def getIndexGrid(self, name):
        """
        Returns GDALGrid object of index map

        Paramters:
            name(str): Name of index map in 'cmt' file.

        Returns:
            GDALGrid
        """
        index_map = self.mapTableFile.indexMaps.filter_by(name=name).one()

        gssha_pro_card = self.getCard("#PROJECTION_FILE")
        if gssha_pro_card is None:
            raise ValueError("#PROJECTION_FILE card not found ...")

        with tmp_chdir(self.project_directory):
            # return gssha grid
            return GDALGrid(index_map.filename,
                            gssha_pro_card.value.strip('"').strip("'"))