Hi John,
all our models use rotated_latitute_longitude. And we have a consistent
way of translating it between grib, proj and netcdf-java, i.e. publicly
available at:
http://thredds.met.no/thredds/catalog/metno/proff4km/default/catalog.html
grid_mapping_name: rotated_latitude_longitude
grid_north_pole_longitude: 156.0
grid_north_pole_latitude: 23.5
earth_radius: 6367470.0
to proj:
proj4: +proj=ob_tran +o_proj=longlat +lon_0=-24 +o_lat_p=23.5
+a=6367470.0 +no_defs
from grib:
lonRot = longitudeOfSouthernPoleInDegrees
latRot = latitudeOfSouthernPoleInDegrees
+proj=ob_tran +o_proj=longlat +lon_0=" << normalizeLongitude180(lonRot)
<< " +o_lat_p=" << (-1 * latRot);
This is the set of parameters which have been useful. I'm not sure if
they are named in a useful way. proj4's ob_tran even allows for a
o_lon_p parameter, but this doesn't seem to be used by grib or CF.
Best regards,
Heiko
On 2013-03-06 15:18, John Caron wrote:
> The "Rotated Pole" projection here:
>
> http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.6/cf-conventions.html#appendix-grid-mappings
>
>
> Rotated pole
>
> grid_mapping_name = rotated_latitude_longitude
>
>
> Map parameters:
>
> *
>
> grid_north_pole_latitude
>
> *
>
> grid_north_pole_longitude
>
> *
>
> north_pole_grid_longitude - This parameter is option (default is 0).
>
> Map coordinates:
>
> The rotated latitude and longitude coordinates are identified by
> the standard_name attribute values
> grid_latitude and grid_longitude respectively.
>
>
>
> is problematic. It has no reference to Proj.4, and is not in Snyder.
>
> Its likely the same as the GRIB-2 GDS Template 3.1:
>
> Grid Definition Template 3.1: Rotated Latitude/longitude (or
> equidistant cylindrical, or Plate Carr?e)
>
> Octet No. Contents
>
> 15-72 Same as Grid Definition Template 3.0 (see Note 1)
>
> 73-76 Latitude of the southern pole of projection
>
> 77-80 Longitude of the southern pole of
> projection
>
> 81-84 Angle of rotation of projection
>
> 85-nn List of number of points along
> each meridian or parallel (These octets are only present for
> quasi-regular grids as described in Note 3)
>
> Notes:
>
>
> (2) Three parameters define a general latitude/longitude
> coordinate system, formed by a general rotation of the sphere. One
> choice for these parameters is:
>
> (a) The geographic latitude in degrees of the southern pole of
> the coordinate system, ?p for example.
>
> (b) The geographic longitude in degrees of the southern pole of
> the coordinate system, ?p for example.
>
> (c) The angle of rotation in degrees about the new polar axis
> (measured clockwise when looking from the southern to the northern pole)
> of the coordinate system, assuming the new axis to have been obtained by
> first rotating the sphere through ?p degrees about the geographic polar
> axis, and then rotating through (90 + ?p) degrees so that the southern
> pole moved along the (previously rotated) Greenwich meridian.
>
>
> Except note that GRIB-2 uses "southern pole of projection". Not sure how
> that affects the algorithm.
>
> The CF parameter "north_pole_grid_longitude" likely should be "Angle of
> rotation".
>
>
>
> Anyone using this or have some insight on it ??
>
>
>
>
> _______________________________________________
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> CF-metadata at cgd.ucar.edu
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>
--
Dr. Heiko Klein Tel. + 47 22 96 32 58
Development Section / IT Department Fax. + 47 22 69 63 55
Norwegian Meteorological Institute http://www.met.no
P.O. Box 43 Blindern 0313 Oslo NORWAY
Received on Wed Mar 06 2013 - 08:03:43 GMT
