[gradsusr] lats4d and used defined variable

[Arlindo da Silva]

On Fri, Feb 25, 2011 at 10:00 AM, Becker, Bernd <
bernd.becker at metoffice.gov.uk> wrote:

>
> Dear all,
> I grapple with lats4d and writing a user defined variable
> in grib_format.
>
> How can I achieve the following:
>
> open file.ctl  (contains tmax amongst other things)
> define pop=tmax/2.
>
> lats4d -v -q -i  file.ctl -vars pop  -o ex2a -format grads_grib
>
> the follwing works just fine:
>
> lats4d -v -q -i  ex2a.ctl -vars tmax  -o ex2a -format grads_grib
>
>

Here is something that should work:

lats4d -v -q -i  ex2a.ctl -vars tmax  -func @/2 -o ex2a -format grads_grib

where '@' will be replaced with the actual variable name. If you really want
to do something more elaborate it may be better for you to write a gsudf
function to handle each one of your variables. For example,

lats4d -v -q -i  ex2a.ctl -vars tmax  -func handler(@)  -o ex2a -format
grads_grib

Nex you implement the "handler" function in a file called "handler.gsf" that
you contain something like that:

function handler(vname)
'define xxx = ' vname '/2
return xxx

The script "handler.gsf" needs to be registered as a (grads script) gs UDF
in your UDXT as explained here:

     http://opengrads.org/doc/udxt/gsudf/

Gs UDF's are very powerful: it allows you to write very complicated
"expression functions" as a simple grads script. For example, these t-storm
related functions were written entirely as gs UDFs:

     http://opengrads.org/doc/udxt/saakeskus/

You will need an opengrads build for using this this feature; use
v2.0.a9.oga.1 if you can, although it should work in v1.x as well.


http://opengrads.org/wiki/index.php?title=Installing_the_OpenGrADS_Bundle

Good Luck,

     Arlindo




> This runs in a 1.9 built.
>
> In the real case, pop is a lot more complicated than tmax/2.
>
> Thanks for your suggestions!
> Have a nice weekend.
> Bernd.
>
> --
> Bernd Becker   Climate Impacts Product Development
> Met Office Hadley Centre    FitzRoy Road  Exeter   Devon EX1 3PB  United
> Kingdom
> Tel.: +44 (0) 1392 884511 Fax: +44 (0)870 900 5050
> E-mail:bernd.becker at metoffice.gov.uk -
> http://www.metoffice.gov.uk/research/our-scientists/seasonal-to-decadal/
> bernd-becker
>
>
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>



-- 
Arlindo da Silva
dasilva at alum.mit.edu
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