Re: [netcdf-java] WRFConvention.java problem.

• To: Todd Plessel <plessel.todd@xxxxxxx>
• Subject: Re: [netcdf-java] WRFConvention.java problem.
• From: John Caron <caron@xxxxxxxxxxxxxxxx>
• Date: Tue, 20 Jul 2010 17:28:10 -0600

On 7/20/2010 4:45 PM, Todd Plessel wrote:

Hi John,

Thanks for looking into this.
To recap...

WRF polar file contents:

Some relevant attributes are:
west_east = 199 ;
south_north = 199 ;
float LU_INDEX(Time, south_north, west_east) ;
:DX = 108000.f ;
:DY = 108000.f ;
:GRIDTYPE = "C" ;
:MAP_PROJ = 2 ;
:CEN_LAT = 90.f ;
:CEN_LON = -8.f ;

:TRUELAT1 = 45.f ;
:TRUELAT2 = 45.f ;
:MOAD_CEN_LAT = 90.f ;
:STAND_LON = -98.f ;

CEN_LON should probably = -98 = STAND_LON
just as CEN_LAT = 90 = MOAD_CEN_LAT.

Code fix:

ucar.nc2.dataset.conv.WRFConvention, to use centralLat ("CEN_LAT") when 
available:
       case 2:
         // Thanks to Heiko Klein for figuring out WRF Stereographic
         double lon0 = (Double.isNaN(standardLon)) ? centralLon : standardLon;
         double lat0 = (Double.isNaN(centralLat)) ? lat2 : centralLat;  // ?? 
7/20/2010
         double scaleFactor = (1 + Math.abs(Math.sin(Math.toRadians(lat1)))) / 
2.;  // R Schmunk 9/10/07
         // proj = new Stereographic(lat2, lon0, scaleFactor);
         proj = new Stereographic(lat0, lon0, scaleFactor);

The code uses STAND_LON instead of CEN_LON.
(These should be the same in the file, but apparently CEN_LON is often bogus.)

apparently

And it computes scale_factor_at_projection_origin = 0.85...
from TRUELAT1 = TRUELAT2 = 45 = secant plane.
That seems correct.
Except there is no way to specify the ellipsoid (e.g., WGS_84, or sphere = 
6,370,000m).

The resulting Projection object is now:

Stereographic type=Projection
  grid_mapping_name = stereographic
  longitude_of_projection_origin = -98.0
  latitude_of_projection_origin = 90.0

  scale_factor_at_projection_origin = 0.8535533905932737

Which now matches the object created from CMAQ polar files.

and that change seems to fix the misalignment.

The LU_INDEX now matches the map lines? Great!

seems to

I will have to run my unit tests to see if anything breaks.

Then please let me know when I can download the updated library.

ok

Thanks, for your help, John.
It will fix VERDI and, if rebuilt, IDV also.

Todd
1-919-541-5500

• References:
  • Re: [netcdf-java] WRFConvention.java problem.
    • From: John Caron