def check_crs(self, dataset):
        '''
        int crs; //.......................................................... RECOMMENDED - A container variable storing information about the grid_mapping. All the attributes within a grid_mapping variable are described in http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.6/cf-conventions.html#appendix-grid-mappings. For all the measurements based on WSG84, the default coordinate system used for GPS measurements, the values shown here should be used.
                crs:grid_mapping_name = "latitude_longitude"; //............. RECOMMENDED
                crs:epsg_code = "EPSG:4326" ; //............................. RECOMMENDED - European Petroleum Survey Group code for the grid mapping name.
                crs:semi_major_axis = 6378137.0 ; //......................... RECOMMENDED
                crs:inverse_flattening = 298.257223563 ; //.................. RECOMMENDED
        '''
        grid_mapping = util.get_crs_variable(dataset)
        if grid_mapping is None:
            return Result(
                BaseCheck.MEDIUM,
                False,
                'Recommended variable for grid mapping should exist',
                ['A variable to describe the grid mapping should exist']
            )
        crs_variable = dataset.variables[grid_mapping]
        test_ctx = TestCtx(BaseCheck.MEDIUM, 'Recommended attributes for grid mapping variable {}'.format(crs_variable.name))
        test_ctx.assert_true(crs_variable is not None, 'A container variable storing the grid mapping should exist for this dataset.')

        epsg_code = getattr(crs_variable, 'epsg_code', '')
        semi_major_axis = getattr(crs_variable, 'semi_major_axis', None)
        inverse_flattening = getattr(crs_variable, 'inverse_flattening', None)

        test_ctx.assert_true(epsg_code != '',
                             'Attribute epsg_code should exist and not be empty: {}'.format(epsg_code))
        test_ctx.assert_true(semi_major_axis is not None,
                             'Attribute semi_major_axis should exist and not be empty: {}'.format(epsg_code))
        test_ctx.assert_true(inverse_flattening is not None,
                             'Attribute inverse_flattening should exist and not be empty: {}'.format(epsg_code))
        return test_ctx.to_result()
int crs; //.......................................................... RECOMMENDED - A container variable storing information about the grid_mapping. All the attributes within a grid_mapping variable are described in http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.6/cf-conventions.html#appendix-grid-mappings. For all the measurements based on WSG84, the default coordinate system used for GPS measurements, the values shown here should be used.
                crs:grid_mapping_name = "latitude_longitude"; //............. RECOMMENDED
                crs:epsg_code = "EPSG:4326" ; //............................. RECOMMENDED - European Petroleum Survey Group code for the grid mapping name.
                crs:semi_major_axis = 6378137.0 ; //......................... RECOMMENDED
                crs:inverse_flattening = 298.257223563 ; //.................. RECOMMENDED