[gradsusr] evaluation of grads expressions in pygrads (galab.py)

[Francesco Benincasa]

* venerdì 25 novembre 2011, alle 12:20, Arlindo da Silva scrive:
[...]
> Can you give us some more details here? Is this a global or regional dataset?

It's a regional dataset.

> Also, which version of pygrasd is this? Platform?
  
pygrads 1.1.4
python 2.6.5
OS OpenSuSE 11.3
 
>     and I've noticed that
>     in some cases the map is drawn correctly only if I use the "transf"
>     option set to True (the projection is cylindric).
> 
> In principle, you should not have to set the "transf" attribute. This is an
> internal parameter to signal the package that a map transformation is
> necessary, "under the hood" kind of stuff.
[...]
> Here is the main issue that drives this special handling. GrADS is very
> flexlible in its addressing of longitudes: [-180,180],  [0,360], [20,380], all
> is fair game. The Basemap toolkit (and the proj4 library it relies on) less so,
> it wants longitudes in the range [-180,180]. Therefore, anytime a map
> transformation is necessary the longitude domain of the input grid get changed
> to the range [-180,180], a map transform is applied, and the the original grid
> arrangement is restored after the transform.

Ah ok, thank you for your explanation.
 
>   I am not exactly clear what your particular problem is. If you send me a
> small sample file I can try it out and fix whatever bugs may be in there. I
> always work with global files, so it is possible that I may have overlooked
> some important detail for regional files (if indeed you have a regional file).

I attach two images, one with the map correctly drawn (with the "transf"
optino set to True) and one with the wrong one. You can download a test
dataset from here:
http://sds-was.aemet.es/archive/files/testfile.nc

I use some different dataset from various models (both global and regional)
and I only have to set the transf option with this model.

Thank you very much.
 
-- 
| Francesco Benincasa
| http://www.linkedin.com/in/fbenincasa
****
Civilization is the limitless multiplication of unnecessary necessities.
        -- Mark Twain