Fwd: Re: Rotated Lat/Lon Grib2 grids

>
> On 8/25/2010 1:46 PM, Robb Kambic wrote:
>> Hi John,
>> 
>> Before you took over the Grib library I was working on a report for Rotated
>> Latitude/Longitude projections. The report is under Support netCDF Decoder 
>> with header/ID Grib2-Data from the german weather service (GVS-648293)
>> 
>> The main point is that the Grib2 data is under regulation:
>> WMO-regulations: "92.1.8 The longitude values shall be limited to the range 
>> 0 to
>> 360 degrees.
>> 
>> This causes problems when the latitude is negative and the longitude is 
>> positive
>> that the projection RotatedLatLon doesn't calculate the correct 
>> coordinates. If the
>> longitude is changed to be negative too, 342 -> -18 then the coordinates 
>> line up correctly. In method
>> 
>> GridHorizCoordSys:makeRotatedLatLon() there is a test for this case and 
>> changes the
>> value of lo1 to negative. The code change is only meant to demostrate the 
>> point, not implementation.
>> 
>> Robb...
>> 
>> private void makeRotatedLatLon(NetcdfFile ncfile) {
>>
>>     double splat = gds.getDouble(GridDefRecord.SPLAT);
>>     double splon = gds.getDouble(GridDefRecord.SPLON);
>>     double spangle = gds.getDouble(GridDefRecord.ROTATIONANGLE);
>>
>>     // Given projection coordinates, need LatLon coordinates
>>     proj = new RotatedLatLon(splat, splon, spangle);
>>
>>     double lat1 = gds.getDouble(GridDefRecord.LA1);
>>     double lon1 = gds.getDouble(GridDefRecord.LO1);
>>     if( lat1 < 0 && lon1 > 0 )
>>       gds.addParam( GridDefRecord.LO1, lon1 -= 360);
>> 
>> =============================================================================== 
>> Robb Kambic                       Unidata Program Center
>> Software Engineer III               Univ. Corp for Atmospheric Research
>> address@hidden           WWW: http://www.unidata.ucar.edu/
>> =============================================================================== 
>

===============================================================================
Robb Kambic        			   Unidata Program Center
Software Engineer III			   Univ. Corp for Atmospheric Research
address@hidden		   WWW: http://www.unidata.ucar.edu/
===============================================================================