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

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

Hi Zhen,
If what you want is a sub-sampling of the data at every second point (or 
other regular interval) in a NetCDF file, then you can use the "strides" 
syntax, [i=LO:HI:STRIDE,j=LO:HI:STRIDE]

 yes? use ocean_density.res.nc
 yes? show grid RHO_TAUM1

! I don't have the file, but if it shows 680 points in x and 380 points 
in the y direction, then
! defining the following variable would read every second point in each 
direction. This is done
! by the call to the netcdf library. 
 yes? let var_ij=RHO_TAUM1[i=2:680:2,j=2:380:2]

! Any value can be used for the stride, and changing the start value 
will sample different points.

 yes? let var_ij = RHO_TAUM1[i=1:680:5,j=1:380:3]


Jaison Kurian wrote:

> Hi Zhen,
>           Yes, SAMPLEIJ needs same length for the ipts and jpts. The
> resulting variable from this external function will have only one
> abstract axis which corresponds to the length of ipts(=jpts) instead
> of X and Y (Z and T will be inherited from the original variable).
>
>   From the values given for ipts (=2,4,6,....,680) & jpts (=2,4,6,..
> ..,380) it seems that you are trying to regrid the density variable
> to a coarser grid (without any averaging) which does have alternate
> positions as grid points. For doing this there are proper methods like
> --> defining a coarser destination grid, regrid the variable onto
> that grid using @XACT regridding. If you can explain what exactly
> you want to do, I can offer you a better help.
>
> Let me know if you have any questions.
>
> Regards,
>
> Jaison
>
> On Wed, 31 May 2006 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