I have been trying to make a netCDF dataset compliant with the CF conventions. The dataset is currently in the EPSG 3411 NSIDC Sea Ice Polar Stereographic projection (i.e., x and y coordinate variables, no Lat/Lon auxiliary coordinate variables). I am trying to make sure the grid mapping variable is set up properly, but I'm not sure which grid mapping to use.

I assumed I should use the Polar Stereographic projection at first, and was trying to make it work, but I am confused by the requirement that the latitude_of_projection_origin attribute should be either +90 or -90, because the corresponding value (I think) for EPSG 3411 in the OGC WKT string is 70. Also, for the third "Map Parameter" listed, it appears that only two EPSG codes (9829 and 9810) might be acceptable, although that's not made explicit.

I looked a bit further and found there is also a plain "Stereographic" grid mapping available, and I wonder if I should use that one instead.

Using pyproj.crs.CRS (3.0.1) and the to_wkt() method, I've found that the EPSG 3411 projection uses the "Polar Stereographic (variant B)" (EPSG 9829) for the "CONVERSION" parameter.

I've also realized that pyproj.crs.CRS has a to_cf() method that creates a dict automatically from the epsg code, and when used with CRS.from_epsg(3411), it follows the convention for the "Polar Stereographic" grid mapping.

So that answers my original question, but there is still room to clear things up:

  • Why doesn't the OGC WKT entry for EPSG 3411 at spatialreference.org include anything about this coordinate system relying on EPSG 9829?
  • Why isn't the "Latitude of origin" included in that WKT string either?
  • You shouldn't rely on third party web sites to get information on EPSG codes, you should use the EPSG registry ~ epsg.org/home.html. Note, that the spatialreference.org home page tells us Last update: 2013
    – nmtoken
    Jul 7 at 8:50
  • Note that NSIDC Sea Ice Polar Stereographic North is EPSG:3413
    – nmtoken
    Jul 7 at 9:03
  • I appreciate it! I have seen spatialreference.org and epsg.io referred to as authoritative (unfortunate) but I can't believe the actual EPSG registry at epsg.org isn't even a top hit on a routine Google search (e.g. "EPSG XXXX"). Looks like EPSG:3411 is deprecated as you point out. The dataset I am using is natively in EPSG:3411, though, as are some older NSIDC datasets. So I still need the archived information, accessible through e.g. epsg.io or python libraries, for working with these data, and my questions still apply to those I believe.
    – kmeanskeal
    Jul 9 at 16:39
  • If you register at epsg.org you can access the deprecated data
    – nmtoken
    Jul 10 at 6:42

The EPSG registry tells us for EPSG:3411 (deprecated)

PROJCRS["NSIDC Sea Ice Polar Stereographic North",BASEGEOGCRS["Unspecified datum based upon the Hughes 1980 ellipsoid",DATUM["Not specified (based on Hughes 1980 ellipsoid)",ELLIPSOID["Hughes 1980",6378273,298.2794111,LENGTHUNIT["metre",1,ID["EPSG",9001]],ID["EPSG",7058]],ID["EPSG",6054]],ID["EPSG",4054]],CONVERSION["US NSIDC Sea Ice polar stereographic north",METHOD["Polar Stereographic (variant B)",ID["EPSG",9829]],PARAMETER["Latitude of standard parallel",70,ANGLEUNIT["degree",0.0174532925199433,ID["EPSG",9102]]],PARAMETER["Longitude of origin",-45,ANGLEUNIT["degree",0.0174532925199433,ID["EPSG",9102]]],PARAMETER["False easting",0,LENGTHUNIT["metre",1,ID["EPSG",9001]]],PARAMETER["False northing",0,LENGTHUNIT["metre",1,ID["EPSG",9001]]],ID["EPSG",19865]],CS[Cartesian,2,ID["EPSG",4468]],AXIS["Easting (X)",South along 45°E],AXIS["Northing (Y)",South along 135°E],LENGTHUNIT["metre",1,ID["EPSG",9001]],ID["EPSG",3411]]

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