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

Heiko,
Your fix corrected both the scaling and right/left flipping issue originally observed by Egil Storen. As it turns out, data files that lack semi-major and semi-minor axis information are handled by one class (projection), while those with the axis information are handled by another (stereographicazimuthalprojection). The latter class had a couple of bugs. Thus, one data file plotted correctly and the other did not. Many thanks!
The correction will be released in IDV4.0, which should be available in an alpha version in the next week. 

Regards,
  Lansing Madry
  Unidata
  Boulder, Colorado

On 1/28/2013 11:55 AM, Heiko Klein wrote:

Hi,
I moved this request to the netcdf-java list, since I can see the problems also in the latest toolsUI. In newer versions (4.3.14) it looks even worth with a different scale (km -> m):
in https://github.com/Unidata/thredds/blob/master/cdm/src/main/java/ucar/unidata/geoloc/projection/proj4/StereographicAzimuthalProjection.java
Please find attached a replacement for above file, fixing both south-pole x-flipping and scale. 

Heiko






On 2013-01-25 16:28, Egil Støren wrote:

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 Støren
   Norwegian Meteorological Institute




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