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Re: [ferret_users] Time axis question



Hi Roman,
The time coordinates that are listed are always the time in the given time units, measured from the time origin.  If the time origin isn't explicitly given in the DEFINE AXIS command, then it is assigned automatically by Ferret.  For your axis, it is the start of the century, so  01-JAN-1610 00 / 1:  3653.  is giving us the number of days since the start of 1600.  You can find the time origin with a SHOW AXIS command:
yes? define axis/t=01-jan-1610:01-feb-1610:6/unit=day timaxis
yes? show axis timeaxis
 name       axis              # pts   start                end
 TIMEAXIS  TIME                 7 r   01-JAN-1610 00:00    06-FEB-1610 00:00
T0 = 01-JAN-1600
   Axis span (to cell edges) = 42

Or, `var,return=t0`
yes? say `t[gt=timeaxis],return=t0`
 !-> MESSAGE/CONTINUE 01-JAN-1600
01-JAN-1600
If you specified a time origin, then it might look like this:
yes? define axis/t=01-jan-1610:01-feb-1610:6/t0=01-jan-1610/units=day timeaxis
yes? list t[gt=timeaxis]
             VARIABLE : T
                        axis TIMEAXIS
             SUBSET   : 7 points (TIME)
 01-JAN-1610 00 / 1:   0.00
 07-JAN-1610 00 / 2:   6.00
 13-JAN-1610 00 / 3:  12.00
 19-JAN-1610 00 / 4:  18.00
 25-JAN-1610 00 / 5:  24.00
 31-JAN-1610 00 / 6:  30.00
 06-FEB-1610 00 / 7:  36.00




Roman Tonkonojenkov wrote:
Hi Ferreters,

I have a simple question about the t pseudo-variable. I wasn't able to find exact answer in the documentation and I have trouble understanding what it refers to [please see exaple file below]
I would be thankful if someone could offer some clarification...

Sincerely,
Roman



 define axis/t=01-jan-1610:01-feb-1610:6/unit=day timaxis
yes? list t[gt=timaxis]
             VARIABLE : T
                        axis TIMAXIS
             SUBSET   : 7 points (TIME)
 01-JAN-1610 00 / 1:  3653.
 07-JAN-1610 00 / 2:  3659.
 13-JAN-1610 00 / 3:  3665.
 19-JAN-1610 00 / 4:  3671.
 25-JAN-1610 00 / 5:  3677.
 31-JAN-1610 00 / 6:  3683.
 06-FEB-1610 00 / 7:  3689.

yes? define axis/t=01-jan-1600:01-feb-1600:6/unit=day timaxis
Replacing definition of axis TIMAXIS

yes? list t[gt=timaxis]
             VARIABLE : T
                &nb! sp;       axis TIMAXIS
             SUBSET   : 7 points (TIME)
 01-JAN-1600 00 / 1:   0.00
 07-JAN-1600 00 / 2:   6.00
 13-JAN-1600 00 / 3:  12.00
 19-JAN-1600 00 / 4:  18.00
 25-JAN-1600 00 / 5:  24.00
 31-JAN-1600 00 / 6:  30.00
 06-FEB-1600 00 / 7:  36.00

yes? define axis/t=01-jan-1900:01-feb-1900:6/unit=day timaxis
Replacing definition of axis TIMAXIS

yes? list t[gt=timaxis]
             VARIABLE : T
                        axis TIMAXIS
             SUBSET   : 7 points (TIME)
 01-JAN-1900 00 / 1:!    0.00
 07-JAN-1900 00 / 2:   6.0! 0
&nb sp;13-JAN-1900 00 / 3:  12.00
 19-JAN-1900 00 / 4:  18.00
 25-JAN-1900 00 / 5:  24.00
 31-JAN-1900 00 / 6:  30.00
 06-FEB-1900 00 / 7:  36.00

yes? define axis/t=01-jan-1910:01-feb-1910:6/unit=day timaxis
Replacing definition of axis TIMAXIS

yes? list t[gt=timaxis]
             VARIABLE : T
                        axis TIMAXIS
             SUBSET   : 7 points (TIME)
 01-JAN-1910 00 / 1:  3273.
 07-JAN-1910 00 / 2:  3279.
 13-JAN-1910 00 / 3:  3285.
 19-JAN-1910 00 / 4:  3291.
 25-JAN-1910 00 / 5:  3297.
 31-JAN-1910 00 / 6:  3303.
 06-FEB-1910 00 / 7:  3309.


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