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19990203: GEMPAK and NetCDF files

Mike,

I provided some routines in GEMPAK to read NetCDF grid files
(that fit the NUWG standard...such as gribtonc produces).
The NUWG basically defines how the CDF files is defined,,
including the grid projection information etc.

As you mention, there are performance drawbacks since
a fair amount of discovery has to be done to figure out
all the ways the a varaible may be defined.

In GEMPAK tempurature is TMPK, regardless of what vertical
coordinate etc it it on. In NetCDF, you can frequently
have T, T_sfc, T_sgma, T_trop etc.

I have written a straight netcdf to gempak file converter
for some of the reanalysis data sets. They don't conform
to the NUWG, so its about inpossible to use them directly.
They do things like give you the lat/lon of every grid
point, but don't tell you what the projection was. 
Luckily its usually ced, but it would be pretty tough to
figure out any other projection without some metadata
to define the projection.

If you have a specific file set, I can help you get it into/out
of gempak format. Thats probably the easiest solution at this time.

Steve

On Mon, 1 Feb 1999, Mike Trexler wrote:

> Hi Steve,
> 
> Thanks for the info about the gf driver.  I'll try it out.  I have a new
> question, though.  This time it's about Gempak and it's relationship
> to netCDF.  The documentation on the web is kind of spotty about
> this.  I spent most of my time looking through the email support
> archives.  Maybe I'm just looking in the wrong place, so if so just
> direct me there.  But...let me tell you what I think to be true and
> you straighten me out.  Ok, netCDF is a more general format than
> the Gempak format and so it is difficult to accurately convert from
> one to the other, especailly from netCDF to Gempak, something
> about the the way the variables are labeled with multiple levels.
> But, Gempak can read netCDF files on the fly and run happy with
> them provided that Gempak was compiled with access to the netCDF
> libraries?  Is this right?  There may be some performance degridation,
> though, for certain programs in Gempak?  right?  Can you direct
> me where to read and/or provide an overview for me.
> 
> Thanks for your help!
> Mike
> 
> --
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