Hi,
We have a dataset with rotated pole in which the projection definition has an unexpected 180 degrees shift if you compare it to the proj definition.
Our WMS derives proj strings for projection from CF projection metadata. In order to visualise CF rotated pole I had to shift grid_north_pole_longitude by 180 degrees, see the following mapping:
float rotated_pole ;
rotated_pole:grid_mapping_name = "rotated_latitude_longitude" ;
rotated_pole:units = "degrees" ;
rotated_pole:grid_north_pole_latitude = 47.000000f ;
rotated_pole:grid_north_pole_longitude = -165.000000f ;
equals to:
"+proj=ob_tran +o_proj=longlat +lon_0=15 +o_lat_p=47 +o_lon_p=0 +a=6378.140 +b=6356.750 +x_0=0 +y_0=0 +no_defs"
Here is a DAP URL if you would like have another example dataset:
http://opendap.nmdc.eu/knmi/thredds/dodsC/RACMO/experiments/RLOTOS50/ndlotos-cy33r1_nmdc-opendap/3Hourly_data/tsurf.KNMI-2011.RLOTOS50.ndlotos-cy33r1_nmdc-opendap.nc
Is this 180 degree shift not supposed to be needed?
Cheers,
Maarten
-----Oorspronkelijk bericht-----
Van: cf-metadata-bounces at cgd.ucar.edu namens Burkhardt Rockel
Verzonden: di 24-4-2012 21:11
Aan: Don.Murray at noaa.gov
CC: cf-metadata at cgd.ucar.edu
Onderwerp: Re: [CF-metadata] rotated pole projection
Hi Don,
this is not a problem in the grid definition, but a problem of the code. This is not just a problem in your Java code, but also in the Fortran code that is used in regional climate models (and the output files in the link you provided are from the Danish regional climate model). It may well be that the Java version was derived from the Fortran version.
This strange thing happens, when the geographic pole and the rotated pole are the same or the rotation is just along the equator. In your case you may either set grid_north_pole_longitude=180. before entering your Java routine or just ignore the rotated pole at all since in this special case it is rlon = geographical longitude and rlat = geographical latitude.
Regards
Burkhardt
Am 24.04.2012 um 18:50 schrieb Don Murray:
> Hi-
>
> I have some climate files that have a rotated-pole projection defined as:
>
> char rotated_pole ;
> rotated_pole:grid_mapping_name = "rotated_latitude_longitude" ;
> rotated_pole:grid_north_pole_latitude = 90.f ;
> rotated_pole:grid_north_pole_longitude = 0.f ;
>
> When I read this through the netCDF-Java library, the data end up 180 degrees off from where it is supposed to be (African data is over Hawaii). I talked to John Caron at Unidata and he doesn't know if it is a problem with the grid definition or the rotated-pole code in netCDF-Java.
>
> Does anyone on this list have a pointer to the equations for the rotated pole and or know if there anything wrong with the grid mapping definition? Should the above imply a unity transformation?
>
> Sample files are at:
>
> http://dods-testbed.ictp.it/aap/ENSEMBLES_AMMA/ERAIN/Daily/
>
> thanks for the help!
>
> Don
> --
> Don Murray
> NOAA/ESRL/PSD and CIRES
> 303-497-3596
> http://www.esrl.noaa.gov/psd/people/don.murray/
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Received on Wed Apr 25 2012 - 02:39:40 BST
