[gradsusr] Faster point output from grb data files

Davide Sacchetti davide.sacchetti at arpal.gov.it
Wed Apr 17 03:44:40 EDT 2013


a PDEF entry is a reason for script to run slower. The reason is that
your data are stored (in grib file) on native grid and grads has to
interpolate grids on "desired" grid (than: extra work to do).
In "ordinary" conditions, let's say XDEF*YDEF ~ 10000 or 100000 I don't
feel PDEF to be slower, but if XDEF*YDEF ~ 1000000 or more grads is
definitively slower.
Hoping it may help ...

a workaround may be to save grids (e.g. using grads fwrite gxout)
directly on interpolated grids (it will be slow, but only once)

bye bye
Davide

On Tue, 2013-04-16 at 23:16 +0000, Sam Wilson wrote:
> Hi,
> 
> 
> I have a set of grads scripts that generate point output of various
> variables (wind, pressure, etc.) for many locations using different
> model datasets in grb format.  I'm using the gr2stn function to get
> the output at the station locations.  Most of my scripts run very
> quickly and generate data for thousands of locations.  However, some
> of them are very slow and will take many hours to get output at all
> the points I want.  The only difference between the scripts are the
> dataset that they are accessing and using to generate the output.  
> 
> 
> I'm trying to determine why some of them run very slow and others do
> not.  I assumed the reason was the size of the grb files being used –
> if the grb files were very large then it would be slower and vice
> versa.  As a test, I decreased the number of variables being included
> in the grb file set that was very large to reduce the size of those
> grb files.  I then ran the script to generate the point output from
> the smaller grb files and it didn't seem to buy me much run time.
> 
> 
> I did notice that the grb files that are associated with the slow
> processing have a PDEF entry in the .ctl file, whereas the grb files
> that process very fast have no PDEF entry.  Could this be the cause?
>  Does it take a lot longer to get point output from data that has to
> be mapped to a rectilinear lat/lon grid (has a PDEF entry) versus data
> that is already on a rectilinear lat/lon grid (no PDEF entry)?  If
> this is the case, does anyone know of a way around this to get faster
> point output from grb files?
> 
> 
> Thanks for your time and any help you can provide.
> 
> 
> Best,
> Sam 
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--> Attenzione cambio indirizzo: davide.sacchetti at arpal.gov.it
--
Davide Sacchetti
Centro Funzionale Meteo Idrologico di Protezione Civile della Regione Liguria
ARPAL Unità Tecnica Complessa di livello Regionale
V.le Brigare Partigiane 2 16121 Genova (I)
tel: +39 010 6437535                    fax: +39 010 6437520
mail: davide.sacchetti at arpal.gov.it     web: www.meteoliguria.it





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