Re: [ferret_users] problem with 'SAMPLEXY'

[jaison@xxxxxxxxxxxxxx]

Hi Sindu,
          Setting region/selecting xpts and ypts along time for SAMPLEXY
input should work just fine, unless and otherwise there is something wrong
with your time axis (or it can be a bug with SAMPLEXY...but hold on...).
However, I will be really surprised if the given script has worked without
any error. Because :

      1. Ferret (or any similar tools) will not allow minus sign (-) in
            variable name, since it is a "special operator/symbol". Ferret
            refers such names as "illegal" (please see user manual,
            Ch3 Sec1.2. File variables, for example), as shown below

            yes? let xpts_jan-dec = 100
                 **ERROR: command syntax: illegal name: XPTS_JAN-DEC
            yes?

      2. The time region syntax is wrong (double quotes are not closed).

So, please do the following :

    - make sure the time axes of lon, lat and wind variables are ok, and
          matches well (number of points, dates etc.)
    - define variables without minus sign (xpts_dec2jan, ypts_dec2jan.....)
    - demonstrate the error with listing few values
    - send a mail back with all details, demonstrating the error.

If you are providing lines from your script, please make sure that you
are making an exact copying. With these details, we can have a better
idea about the problem....and a better solution!

Thanks and Regards,

Jaison



> Dear Ferreters,
> I'm facing a problem with the function SAMPLEXY as I use it to pick out
> values from a gridded dataset (eg wind speed).
>
> I have xpts and ypts from Jan-Dec and I select the lat,lon points
> in 2 ways: 1) Jan-Dec and 2) May-Oct.
>
> The wind values I obtain when I select xpts & ypts from Jan-Dec are
> different from when they are selected only for May-Oct.
> Please see my script below.
>
> 1. Why isnt the wind during May-Oct in both cases identical? &
> 2. Why does the May-Oct selection give me wind data from Jan-Dec?
>
> Am I missing something important while selecting the lat and
> lon points in time and using it in combination with SAMPLEXY ?
>
> Thanks
> Sindu
>
> ------ script-----------------------------------------------
>
> let xpts_jan-dec = longitude[t="01-jan-2006:00:00":"31-dec-2006:00:00]
> let ypts_jan-dec =  latitude[t="01-jan-2006:00:00":"31-dec-2006:00:00]
> let winds_jan-dec = SAMPLEXY(wind,xpts_jan-dec,ypts_jan-dec)
>
> let xpts_may-oct = longitude[t="01-may-2006:00:00":"31-oct-2006:00:00]
> let ypts_may-oct =  latitude[t="01-may-2006:00:00":"31-oct-2006:00:00]
> let winds_may-oct = SAMPLEXY(wind,xpts_may-oct,ypts_may-oct)
>
> ------ script-----------------------------------------------
>
>
> Sindu Raj Parampil
> Ph.D Student
> Centre for Atmospheric and Oceanic Sciences
> Indian Institute of Science
> Bangalore-12
> INDIA
> =========================================================================
> "You don't understand anything until you learn it more than one way."
>                                     Marvin Minsky, 'The Society of Mind'
> =========================================================================
>