def check_var_coverage_content_type(self, ds):
        '''
        Check coverage content type against valid ISO-19115-1 codes

        :param netCDF4.Dataset ds: An open netCDF dataset
        '''
        results = []
        for variable in cfutil.get_geophysical_variables(ds):
            msgs = []
            ctype = getattr(ds.variables[variable],
                            'coverage_content_type', None)
            check = ctype is not None
            if not check:
                msgs.append("coverage_content_type")
                results.append(Result(BaseCheck.HIGH, check,
                                      self._var_header.format(variable), msgs))
                continue

            # ISO 19115-1 codes
            valid_ctypes = {
                'image',
                'thematicClassification',
                'physicalMeasurement',
                'auxiliaryInformation',
                'qualityInformation',
                'referenceInformation',
                'modelResult',
                'coordinate'
            }
            if ctype not in valid_ctypes:
                msgs.append("coverage_content_type in \"%s\""
                            % (variable, sorted(valid_ctypes)))
                results.append(Result(BaseCheck.HIGH, check, # append to list
                                      self._var_header.format(variable), msgs))

        return results
Check coverage content type against valid ISO-19115-1 codes

        :param netCDF4.Dataset ds: An open netCDF dataset