Dear Kamoru Abiodun Lawal,

Probably following's script is what you need.
Hope it helps.

Best,

dessy
=============


!    Purpose: crop, fine resolution, and save to new nc file
!    panggil file nc
use "/home/dessy/Downloads/jan_rain.nc"

!    fine resolution processing by define the grid and grid size
define axis/x=16e:33e:0.2unit=longitude xfine
define axis/y=-22s:-35s:0.2/unit=latitude yfine
define grid/x=xfine/y=yfine gfine

!    save the result of fine resolution to the nc-file
!    -->note: please take a look carefully at L-part (start and end as you need) by command show data
LET/units="`Kg/m^2/s,RETURN=units`"/TITLE="prate_fine" prate_fine = prate[l=start:end,g=gfine]

!    to treat error exceeds memory, it is better to set memory/size to increase memory
set memory/size=300

!    save fine resolution to nc file
SAVE/FILE="/home/dessy/ncdata/rainfine.nc" prate_fine

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From: Kamoru Abiodun Lawal <lawal_ka@xxxxxxxxxxx>
To: Ferret Users <ferret_users@xxxxxxxx>
Sent: Thursday, June 28, 2012 8:46 PM
Subject: [ferret_users] Regridding to retain K and L

Dear Ferreters,
I wish to regrid and at the same time want to maintain my K and L for the data below--------

yes? use Jan_Rain.nc
yes? sh d
     currently SET data sets:
    1> ./Jan_Rain.nc  (default)
 name     title                                      I         J                K         L
 PR       Precipitation                    1:110     1:100     1:1600    1:50
 GLOBAL_LATITUDE
                                                     1:110     1:100          ...       ...
 GLOBAL_LONGITUDE
                                                     1:110     1:100          ...       ...

I ran the script below, which worked to some extent------

  can data /all
  cancel windows /all
  set win /new
  set memory/size = 172800000
  use Jan_Rain.nc
  !  This defines the domain of interest and regular regriddings and spacings.................
  define axis/x=16:33:0.2 xax5
  define axis/y=-35:-22:0.2 yax5
!  This part serialises the domain data................ 
  let slon = xsequence(GLOBAL_LONGITUDE[i=28:63,j=11:40])  !...... Fit the domain here
  let slat = xsequence(GLOBAL_LATITUDE[i=28:63,j=11:40]) 
  let PRECIP = xsequence(PR[i=28:63,j=11:40,k=1:1600,l=1:50])     !....... Change Variable to your desired variable here 
  let rainfall = scat2gridlaplace_xy(slon,slat,precip[k=1:1600,l=1:50],x[gx=xax5],y[gy=yax5],5.,25)
  save /clobber/file =JanRain.nc rainfall

The result is shown below----

yes? use JanRain.nc
yes? sh d
     currently SET data sets:
    1> ./JanRain.nc  (default)
 name                                         title                                              I         J         K         L
 RAINFALL SCAT2GRIDLAPLACE_XY(SLON,SLAT,P  1:86      1:66      ...       ...
 
Please can someone help me?, I want to retain my K and L.
Cheers!
 
Kamoru Abiodun LAWAL
Climate System Analysis Group,
Department of Environmental and Geographical Science,
University of Cape Town, Private Mail Bag X3,
Rondebosch, Cape Town, 7701, South Africa.