5.6 Grid Mappings and Projections
Requirements:

• The type of the grid_mapping attribute is a string whose value is of the following form, in which brackets indicate optional text:

grid_mapping_name[: coord_var [coord_var ...]] [grid_mapping_name: [coord_var ... ]]

• Note that in its simplest form the attribute comprises just a grid_mapping_name as a single word.

• Each grid_mapping_name is the name of a variable (known as a grid mapping variable), which must exist in the file.

• Each coord_var is the name of a coordinate variable or auxiliary coordinate variable, which must exist in the file. If it is an auxiliary coordinate variable, it must be listed in the coordinates attribute.

• The grid mapping variables must have the grid_mapping_name attribute. The legal values for the grid_mapping_name attribute are contained in Appendix F.

• The data types of the attributes of the grid mapping variable must be specified in Table 1 of Appendix F.

• If present, the crs_wkt attribute must be a text string conforming to the CRS WKT specification described in reference [OGC_CTS].

• reference_ellipsoid_name, prime_meridian_name, horizontal_datum_name and geographic_crs_name must be all defined if any one is defined.

• If projected_crs_name is defined then geographic_crs_name must be also.

Recommendations:

• The grid mapping variables should have 0 dimensions.