Re: change T-axis

[Jaison Kurian <jaison@xxxxxxxxxxxxxxxxxx>]

Hi Gao Rongzhen,
                  You need to assign a new time axis for that variable.
You can assign a new time axis in two ways: 1) define a new time axis
and use regridding utilities (like @ASN), 2) use RESHAPE function to 
change the grid of a the variable to that of a second variable. I think
the second method will be more flexible. Please refer user manual ( @ASN:
Ch4 Sec2.4.1.  Regridding transformations , RESHAPE:Ch3 Sec2.3.23.  
RESHAPE )
for details. Here is an example using monthly_navy_winds dataset with 
neccessary details. If you need any mode clarification please let me know.

With Regards 

Jaison

!--------example.jnl---------------------

     set data monthly_navy_winds  ! dataset available with Ferret

     let l_lo =  13     ! low  value for L   
     let l_hi = 120     ! high value for L

     let u = uwnd[d=1,l=`l_lo`:`l_hi`]  ! extract the subset data
   
! now extract the time values corresponding to the subset; needed 
! only if the original variable is on a calendar time axis

     let t_data = T[gt=uwnd,l=`l_lo`:`l_hi`]

! get other details about the original time axis
 
     define symbol t_units = `u,r=TUNITS`    ! time units (days/hours...)
     define symbol t_zero  = `u,r=T0`        ! Ref. time 
     define symbol t_cal   = `u,r=CALENDAR`  ! calendar type
 
! define a destination time axis with these details
 
     define axis/t/T0="($t_zero)"/units=($t_units)/CALENDAR=($t_cal)/\
            from_data tsub=t_data  

! suppose your original variable is not on a "CALENDAR" time
! axis, then just after extracting the subset, define an abstract "T" 
! axis like
!           yes? define axis/t=1:`l_hi-l_lo+1`:1 tsub 
! and use this in the following sequence of commands
   
! create a new variable "t_stamp"  on the destination grid with XYT grid
!                           put + Z[gz=u]*0 if needed

    let t_stamp = X[gx=u]*0 + Y[gy=u]*0 + T[gt=tsub]  ! destination grid

    let u_t = RESHAPE(u,t_stamp)   ! put variable on the destination grid

! comparison

    list/x=60/y=10/l=1:20 u
    list/x=60/y=10/l=1:20 u_t

    plot/x=60/y=10 u_t, u

! now you can use u_t ; for u_t "/L=1" ==> first point on time axis

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



On Wed, 5 Jan 2005, [gb2312] ¸ßÈÙÕä wrote:

> Hi, all
> 
> I have a time series with length N=191. 
> And now, i want to select part of the data from N=13 to 191 to form a new variable. 
> By,  let ccoral=coral[d=1,l=13:191] 
> Now,  list/l=1:20 ccoral 
> The information shown on the screen is as below:
> ------------------------------------------------------------
> VARIABLE : CORAL[D=sst4503-9211s.asc,L=13:191]
> SUBSET   : 8 points (TIME)
> 13:  0.4100
> 14: -0.0900
> 15: -0.8500
> 16: -0.2800
> 17: -0.2700
> 18:  0.0500
> 19: -0.2800
> 20:  0.3300
> ------------------------------------------------------------
> My problem is the defination of T-axis of the new variable.
> What i wanted is the first value of ccoral starts from L=1 not from L=13, and the last value ends with L=179 not with L=191. Is there a way by Ferret to change the T-axis of the new  variable ccoral? 
> 
> Thanks in advance.
> 
> Gao Rongzhen
> 

-- 
___________________________________________________

    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
___________________________________________________