[gradsusr] How to mask out areas outside Mississippi basin ?

[Charles Seman]

Bo,

One thing to try would be to define a 2D mask field as initially 
undefined everywhere using const(somevar,undef_value,-a), then replace 
the values in the mask that you want to use with a value of "1" using 
"set defval"...

Some script code (NOT tested!):

'sdfopen your_file.nc'

'q ctlinfo'
rec3 = sublin(result,3)
undef_value = subwrd(rec3,2)

'q file'
rec5 = sublin(result,5)
nx = subwrd(rec5,3) ; ny = subwrd(rec5,6)

'set x 1 'nx
'set y 1 'ny
'set z 1'
'set t 1'
'define basinmask = const(somevar,'undef_value',-a)'

* next, adapt the code from defval_demo.gs within a loop to
* interactively select points to change from undefined to a value of
* "1"... this would be somewhat tedious, but after defining the
* basinmask variable you could also write it out for future use to a
* GrADS binary file using "fwrite" (or if you are running a version of
* GrADS which has "sdfwrite", to a netCDF file)...

continue = yes
while ( continue = yes )
   say 'Enter "yes" to continue updating points...'
   pull continue
   if ( continue == yes )
*   ...use code from "defval_demo.gs" to update a point
   else
     break
   endif
endwhile

some reference links:
http://grads.iges.org/grads/gadoc/gradfuncconst.html
http://grads.iges.org/grads/gadoc/gradcomdsetdefval.html
ftp://grads.iges.org/grads/scripts/defval_demo.gs
http://grads.iges.org/grads/gadoc/script.html#standardio
http://grads.iges.org/grads/gadoc/script.html#while

Hope this helps,
Chuck

On 03/01/2012 01:01 PM, bo-dong at huskers.unl.edu wrote:
> Dear All,
>
> I have a netcdffile with data covered the U.S., but I only want to
> display the area of Mississippi River basin. Any idea about how to mask
> out areas outside Mississippi River basin? Also, I need to do a basin
> average (i.e. average all the data within Mississippi river basin), the
> aave() function seems to average all the areas in U.S., not only in the
> river basin.
>
> Your assistance is greatly appreciated.
>
> Thanks,
>
> Bo
>
>
>
> _______________________________________________
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> gradsusr at gradsusr.org
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-- 

Please note that Charles.Seman at noaa.gov should be considered my NOAA
email address, not cjs at gfdl.noaa.gov.

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  Charles Seman                                Charles.Seman at noaa.gov
  U.S. Department of Commerce / NOAA / OAR
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