Re: [thredds] Curious effect from attributes semi_major/minor_axis on southern hemisphere images created by ncWMS

• To: "thredds@xxxxxxxxxxxxxxxx" <thredds@xxxxxxxxxxxxxxxx>
• Subject: Re: [thredds] Curious effect from attributes semi_major/minor_axis on southern hemisphere images created by ncWMS
• From: Jon Blower <j.d.blower@xxxxxxxxxxxxx>
• Date: Mon, 28 Jan 2013 13:24:42 +0000

Dear Egil,

My guess would be that the problem lies in the underlying Java-NetCDF libraries 
- hopefully one of the relevant folk can reply to confirm or deny!  I wonder if 
this is fixed in a more recent version of THREDDS?

Best wishes,
Jon

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Message: 1
Date: Fri, 25 Jan 2013 16:28:32 +0100
From: Egil St?ren <egil.storen@xxxxxx>
To: thredds@xxxxxxxxxxxxxxxx
Cc: ?ystein God?y <o.godoy@xxxxxx>,     Steinar Eastwood
        <steinar.eastwood@xxxxxx>,      Arild Burud <arild.burud@xxxxxx>
Subject: [thredds] Curious effect from attributes
        semi_major/minor_axis on southern hemisphere images created by ncWMS
Message-ID: <5102A4A0.5060002@xxxxxx>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Dear all,

We have a netCDF file containing ice concentrations around antarctica that is 
available at 
http://thredds.met.no/thredds/catalog/egiltest/ES/data/catalog.html?dataset=egiltest/ES/data/iceconc.nc.
 
Using the Godiva2 viewer, it is obvious that the data is displayed inverted 
along a vertical line centred on the map. This is most easily seen using the 
south polar stereographic projection.

The netCDF file has a variable containing projection info:

        int Polar_Stereographic_Grid ;
                Polar_Stereographic_Grid:grid_mapping_name = 
"polar_stereographic" ;
                Polar_Stereographic_Grid:straight_vertical_longitude_from_pole 
= 0.f ;
                Polar_Stereographic_Grid:latitude_of_projection_origin = -90.f ;
                Polar_Stereographic_Grid:standard_parallel = -70.f ;
                Polar_Stereographic_Grid:false_easting = 0.f ;
                Polar_Stereographic_Grid:false_northing = 0.f ;
                Polar_Stereographic_Grid:semi_major_axis = 6378273.f ;
                Polar_Stereographic_Grid:semi_minor_axis = 6356890.f ;
                Polar_Stereographic_Grid:proj4_string = "+proj=stere +a=6378273 
+b=6356889.44891 +lat_0=-90 +lat_ts=-70 +lon_0=0" ;

When I removed the following attributes from this variable, the data suddenly 
displayed correctly in Godiva2:

                Polar_Stereographic_Grid:semi_major_axis = 6378273.f ;
                Polar_Stereographic_Grid:semi_minor_axis = 6356890.f ;

The modified version can be seen at
http://thredds.met.no/thredds/catalog/egiltest/ES/data/catalog.html?dataset=egiltest/ES/data/iceconc_1.nc.

Since these attributes only gives a more exact description of the shape of the 
earth (compared to not having them), I think there must be a bug somewhere. 
Have anybody experienced this behaviour? Is this a known bug?

We are using thredds version 4.2.9.

Best regards,

   Egil St?ren
   Norwegian Meteorological Institute



End of thredds Digest, Vol 48, Issue 14
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