Hi Heiko:
So
grid_north_pole_longitude =
normalizeLongitude180(longitudeOfSouthernPoleInDegrees)
grid_north_pole_latitude = -1 * longitudeOfSouthernPoleInDegrees
?
where does one find documentation on proj4's ob_tran routine?
thanks,
John
On 3/6/2013 8:03 AM, Heiko Klein wrote:
> 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 ??
>>
>>
>>
>>
>> _______________________________________________
>> CF-metadata mailing list
>> CF-metadata at cgd.ucar.edu
>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>>
>
Received on Wed Mar 06 2013 - 09:09:25 GMT
