Re: reduced grid an pyNIO

From: David Brown <dbrown_at_nyahnyahspammersnyahnyah>
Date: Tue, 11 Nov 2008 16:38:45 -0700

Jim,
Sorry, it looks like the URL only gives the calling sequence for the
qu2reg3 routine. However, if you were so inclined you could
download the whole GRIBEX package from
http://www.ecmwf.int/publications/manuals/libraries/gribex/
gribexIntroduction.html
  -dave

On Nov 11, 2008, at 4:32 PM, David Brown wrote:

> Hi Jim,
> PyNIO automatically expands reduced (quasi-regular in GRIB-speak)
> grids using (by default) a cubic interpolation algorithm.
> The code is from the ECMWF GRIBEX package, and the specific
> function is qu2reg3.F. You can examine the source at this URL:
>
> http://www.ecmwf.int/publications/manuals/libraries/gribex/
> qu2reg3.F.html
>
> The NIO library modifies this code slightly in order to dynamically
> allocate some work arrays from the calling C code and to
> adjust the error handling.
>
> There is a GRIB-specific file option ('ThinnedGridInterpolation')
> that allows you to switch the interpolation mode between 'cubic'
> and 'linear'. This just adjusts the qu2reg3 KCODE argument. Note
> that if there are any missing values in the data, then the 'linear'
> method is forced.
>
> I would be interested to know how the values differ. Dave
> Stepaniak, from the Data Support Services here at NCAR has done some
> fairly rigorous testing of the ECMWF code and concluded that the
> qu2reg3 'cubic' method was significantly more accurate than the
> 'linear'
> method and as good as another candidate method. That is why 'cubic'
> is the default in PyNIO.
> -dave
>
>
> On Nov 11, 2008, at 3:51 PM, James Boyle wrote:
>
>> I have a grid file from ECMWF. The CDO ( Climate Data operators)
>> say that it contains a reduced gaussian grid.
>> I can expand the grid using the CDOs to a full gaussian grid.
>>
>> when I read a variable using pyNIO from the expanded full gaussian
>> grid file and the original 'reduced?' grid, both variables are on
>> the full grid.
>> but the values are not the same
>>
>> What does pyNIO do with variables on a reduced grid? I fully
>> expected to get an error when I read a reduced grid file.
>>
>> --Jim
>> _______________________________________________
>> pyngl-talk mailing list
>> List instructions, subscriber options, unsubscribe:
>> http://mailman.ucar.edu/mailman/listinfo/pyngl-talk
>
> _______________________________________________
> pyngl-talk mailing list
> List instructions, subscriber options, unsubscribe:
> http://mailman.ucar.edu/mailman/listinfo/pyngl-talk

_______________________________________________
pyngl-talk mailing list
List instructions, subscriber options, unsubscribe:
http://mailman.ucar.edu/mailman/listinfo/pyngl-talk
Received on Tue Nov 11 2008 - 16:38:45 MST

This archive was generated by hypermail 2.2.0 : Fri Nov 14 2008 - 16:43:44 MST