Re: subsampling of grided data onto point location and time.

[Jaison Kurian <jaison@xxxxxxxxxxxxxxxxxx>]

Hi Yogesh,
           If you 'just' want to get the data at a particular point from
a gridded file to a new variable then use 'let' command to extract the
data like..
    
        !suppose you want to get data at 59E and 1S

          set data coads_climatology

        ! to get 12 values corresponding to each month

        LET airt_x59E_y1S = airt[X=59E,Y=1S,l=1:12] 

        ! to get 1 value  corresponding to APR-15

        LET airt_x59E_y1S = airt[X=59E,Y=1S,t="15-APR"]

You can use this new variable to compare with the second "point"
dataset values. Or if you want to fix the location according to 
the second dataset then you have to make sure that you have common
lat, lon & time points in both the datasets. If you want a better
feedback please post the result of 'ncdump -c' for both the NetCDF
files and explain exactly what you want do with these two datasets
..(like comparison of time series). Anyway here is a quick example.

Hope This Helps

With Regards 

Jaison 

!----------example.jnl-----------------------
    set data coads_climatology  ! gridded data
    sh da                       ! see the contents 

    ! let us create some "point data"
    !   suppose data at one particular location say..59E,1S
    !   is available for mid-day of each month for one year 
    !   (for conviniece take it as 0000 to match with coads
    !   climatology)

    let tair = TSEQUENCE({26.3,27.4,27.2,26.9,28.0,27.9,28.3,\
                          28.3,28.5,28.7,28.2,27.8})
    let lonx = 59
    let laty = -1
    
    DEFINE AXIS/t="16-JAN-0000:00":"16-DEC-0000:00":`365.2425/12`/\
                units=days/T0="01-JAN-0000:00" tmon
    DEFINE AXIS/x=`lonx`:`lonx`:1/units=longitude xaxlon
    DEFINE AXIS/y=`laty`:`laty`:1/units=latitude  yaxlat

    let xyt_stamp = X[GX=xaxlon] *0 + Y[GY=yaxlat] *0 + T[GT=tmon]*0
    let tair_xyt  = RESHAPE(tair,xyt_stamp)

    plot tair_xyt-airt[d=1,x=59,y=1S,l=1:12]

!-----------------end of example.jnl---------------  


On Fri, 12 Nov 2004, Yogesh K. Tiwari wrote:

> Hello Ferret Users,
> 
> How I can do the subsampling of a grided data on a given point location 
> and time.
> 
> Both the grided data and point data are in netcdf format.
> 
> The grided data looks like, for example :
> 
> title         I        J      K        L
> CO2_mod     1:360    1:180   --      1:100
> 
> here L is time steps.
> 
> And point data looks like :
> 
> title         I        J      K        L
> CO2_sat      --       --      --    1:1860206
> lat          --       --      --    1:1860206
> lon          --       --      --    1:1860206
> 
> here L is number of index.
> 
> I could not get much help from ferret users guide.
> 
> Many thanks in advance,
> 
> Regards,
> Yogesh
> 
> 
> 
> 
> 

-- 
___________________________________________________

    Jaison Kurian                           
    Centre for Atmospheric and Oceanic Sciences
    Indian Institute of Science
    B A N G A L O R E   560 012
    Ph: +91-80-3942505
        +91-80-3600450
    Fax:+91-80-3600865
___________________________________________________