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Re: WRFConvention.java problem.

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  • Subject: Re: WRFConvention.java problem.
  • Date: Sat, 10 Jul 2010 09:59:37 -0600
Todd Plessel wrote:

Hi John,

We are displaying WRF polar stereographic gridded files
in VERDI - a Java application that uses
netcdf-4.1 Java which contains WRFConvention.java.

http://www.unidata.ucar.edu/software/netcdf-java/v4.1/javadocAll/index.html

Apparently the map is not being projected correctly.
The attached zip file contains a sample WRF NetCDF
data file wrfinput_d01 and screen.gif which shows
correct CMAQ (M3IO NetCDF) data and map on the left and
WRF land-use data and mis-matched map on the right.
The grids are almost identical and so should display
almost the same. Note that South America and
Africa are clearly mis-registered with respect to the
land-use data where (most/all) red is ocean.

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 looks suspect. Perhaps it should be -98?
In any case, which attributes are actually used by
WRFConventions?

I don't see any information about the ellipsoid in the file.
CMAQ usually uses a sphere of radius 6,370,000 meters.
Perhaps WRF does too.
It would seem that the constructors for all projectors should
have ellipsoid input parameters e.g.,
double major_semiaxis,  double minor_semiaxis.

Is there a fix available?

Thanks,

Todd
1-919-541-5500


Hi Todd:

This is what we are using:

 Stereographic type=Projection
   grid_mapping_name = stereographic
   longitude_of_projection_origin = -98.0
   latitude_of_projection_origin = 45.0
   scale_factor_at_projection_origin = 0.8535533905932737
   impl.class= ucar.unidata.geoloc.projection.Stereographic

Do you know what version of WRF generated this? I have a note that says

* Note: Apparently WRF netcdf files before version 2 didnt output the 
projection origin, so
* we cant properly georeference them.

Can you send me the M3IO file? If its the same projection, that might give us a 
clue.