[ferret_users] Re: [Ferret_Users] SAMPLEIJ of an array of size [680,380]

[Ansley Manke <ansley.b.manke@xxxxxxxx>]

Hi Zhen,
The function SAMPLEIJ samples the function at a set of coordinate pairs 
(xpts,ypts) where the x coordinates of the sample points are listed in 
argument 2 and the y coordinates are listed in argument 3.  So yes, the 
number of points in argument 2 and in argument 3 must be the same and if 
they are not, Ferret will use the first n pairs of (xpts,ypts) where n 
is the size of the smaller list, 380 in your case.

Here is a simple example:

     yes?     ! define a simple grid and variable
  yes? def axis/x=1:51:10 xax
  yes? def axis/y=1:3:1 yax
  yes? let var = i[gx=xax]+10*j[gy=yax]

  yes? list var
               VARIABLE : I[GX=XAX]+10*J[GY=YAX]
               SUBSET   : 6 by 3 points (X-Y)
               1     11     21     31     41     51   
               1      2      3      4      5      6
   1   / 1:  11.00  12.00  13.00  14.00  15.00  16.00
   2   / 2:  21.00  22.00  23.00  24.00  25.00  26.00
   3   / 3:  31.00  32.00  33.00  34.00  35.00  36.00

  yes? let xpts = {1,41,11}
  yes? let ypts = {3,1,2}
  yes? list sampleij(var,xpts,ypts)
               VARIABLE : SAMPLEIJ(VAR,XPTS,YPTS)
               SUBSET   : 3 points (X)
   1   / 1:  31.00
   2   / 2:  15.00
   3   / 3:  22.00


The function returns the value of the variable at the locations of the 
coordinate pairs  (xpts,ypts) = (1,3) , (41,1), and  (11,2).

What did you want from the function?  I'm sure we can help you define 
things so that you can return the result you want.

Ansley

zhen.li@gsfc.nasa.gov wrote:

> Dear Ferret_Users:
>
> It seems to me that SAMPLEIJ only subsamples the array that has the 
> same number of
> points in "i" and "j" direction. For example, my effort to use the 
> following
> script to subsample the array of size [680,380] failed, because it 
> only subsampled
> the point in the "I" direction. The new array "var_ij" has a size of 
> [390,1]. I wonder
> if anyone can help me with this case.
>
> !FILE/VAR="ipts" ipts.dat (ipts=2,4,6,....,680)
> !FILE/VAR="jpts" jpts.dat (jpts=2,4,6,....,380)
> !use ocean_density.res.nc
> !let var_ij=sampleij(RHO_TAUM1,ipts[d=1],jpts[d=2])
>
> Thanks!
>
> Zhen