For fm_wkt_unit_params, a
list of named unit definitions
For fm_wkt_get_lengthunit, a
list of length units used in the wkt string, excluding the ellipsoid radius
unit.
For fm_wkt_set_lengthunit, a
WKT2 string with altered length units.
Note that the length unit for the ellipsoid radius is unchanged.
For fm_crs_get_wkt, WKT2 string.
For fm_crs_get_lengthunit, a
list of length units used in the wkt string, excluding the ellipsoid radius
unit. (For legacy PROJ4 code, the raw units from the proj4string are
returned, if present.)
For fm_crs_set_lengthunit, a sp::CRS object with
altered length units.
Note that the length unit for the ellipsoid radius is unchanged.