Re: [ferret_users] time axis definition and precision

[peter hoor <hoor@xxxxxxxxxxxxxxxxx>]

Thanks Martin,

that works fine for daily files. But how to deal with the data, when they 
cover -lets day a whole year or more?
The problem is, that you need the full information in seconds for a year, but 
the variable to create the time axis is modified (see below).

Any idea?


let xmpl=DAYS1900(1900,12,31)
let secs={1,2,3,4,5,6,7,8,9}
list/format="(f14.2)" xmpl*86400+secs
list/format="(f14.2)" xmpl*86400+secs
             VARIABLE : XMPL*86400+SECS
             BAD FLAG : -9.9999998E+33
             SUBSET   : 9 points (X)
             X        : 0.5 to 9.5
   31449600.00
   31449602.00
   31449604.00
   31449604.00
   31449604.00
   31449606.00
   31449608.00
   31449608.00
   31449608.00


 
Am Dienstag, 20. Mai 2008 14:50 schrieb Martin Schmidt:
> Peter,
> I had the same problem several times.
>
> To read daily data with a period of 1 s from a file, where times have
> the form
>
> 2008-02-19 00:00:00
> 2008-02-19 00:00:01
> ...
>
> I do the following:
> let offset = DAYS1900 ( 2008, 1, 1)
> define axis/x/x=1:86400:1 xax
> define grid/x=xax xg
> COLUMNS/deli=" "/grid=xg $1
> let v1o=v1-offset
> define axis/t/from_data/t0=1-jan-2008/unit=days time=v1o+v2/24 + 1e-5
> define grid/t=time tgrid
>
>  From now on things work well.
>
> Two things are needed, the offset to keep the time values limited and
> the 1.e-5. Otherwise I get the same error message as you have got.
>
> There are several show-ups of single precision limitations:
> - long time axes with small time periods
> - strong zooming of other axes, which gives occasionally good looking
> but wrong plots
> - seawater thermodynamics, i.e. relations between salinity, temperature
> pressure and conductivity and so on ...
>
> Greetings,
> Martin

-- 
+++++++++++++++++++++++++++
Dr. Peter Hoor
Max Planck Institute for Chemistry
Dept: Atmospheric Chemistry
P.O.Box 3060 
D-55020 MAINZ
Germany

Tel.: +49 6131 305329
Fax.: +49 6131 305436