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Re: [netcdf-java] GRIB-2-netCDF Projection Question

On 6/25/2012 1:20 PM, Rockwood, Bryan wrote:

John,

Thanks for the quick response.


1.       Sadly, I'm just a recipient of the netCDF files created by the v4.0 
API and the upstream source of this data is not planning on upgrading anytime 
soon.  That said, I expected you guys might say that so I did verified that the 
code works this way in 4.3 too.
if you have a netcdf file, you are not constrained to use the code that created it. 



2.       Understood.  I've already finished the code that does the netCDF -> GRIB 
conversion so this was more of a "why does it work that way?" type of email.

3.       Gotcha.  I wasn't even thinking of it from a GIS standpoint.  After 
spending time  writing code that handles GRIB data, I'm used to the first point 
in a GRIB record being 0,0 and going from there.  The only reason I brought it 
up was that it was the first indication that the projection being used to 
generate the x and y is not using LA1 and LO1 as the originating point.

4.       I'm guessing this is where I'm getting hung up.  All this time, I've 
been working with  the assumption that LA1 and LO1 from the GDS was origin of 
the projection.  How was it decided that LATIN1 and LOV were going to be used 
for the origin instead?  I've talked to a two other software devs who work with 
GRIB (full disclosure, one is a meteorologist, the other is not), and they 
haven't seen it done this way either.


Im guessing that you are confusing two things:

1) the (0,0)th point (eg the upper right grid point) in index space
2) the (lat, lon) location where x=0, y=0 on the projection plane. This is typically placed near the middle of the grid to minimize distortion.
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