Re: determine T0 from Netcdf header

[Jaison Kurian <jaison@xxxxxxxxxxxxxxxxxx>]

Hi Steve Knox,
                In Ferret, you can derive lot of informations about the
variable in a NetCDF file. Please have a look at the user manual for
the key word "RETURN". Here is an example :
 
        ! please note that "RETURN" is used within grave accents (``)  

        yes?  set data monthly_navy_winds ! dataset available with Ferret
        yes?  define symbol t_zero  = `uwnd,r=T0` ! r ==> RETURN
        yes?  define symbol t_units = `uwnd,r=TUNITS`
        yes?  define symbol t_cal   = `uwnd,r=CALENDAR`
        yes?  show symbol t_zero, t_units,  t_cal
          T_ZERO = "14-JAN-1980 14:00:00"
          T_UNITS = "hour"
          T_CAL = "GREGORIAN"

 So "define symbol" command along with "RETURN" will help us to get
the neccessary informations in seperate variables. Please note that
it will be safe to put the ($t_zero) in double quotes(" ") wherever it is
used beacause it may contain the hr:min:sec along with the date, 
seperated by a blank space. To define a new time axis from these 
informations 

       yes? define axis/t=10-JAN-2000:10-DEC-2000:1/units=($t_units)/\
       ...?      t0="($t_zero)"/CALENDAR=($t_cal) tax

 Suppose you want to get "T0" without the hr:min:sec string. Then use
"SUBSTRING" command to extract only the date as follows :

       yes? define symbol t_z = `SUBSTRING("($t_zero)",1,11)` ! in grave accents
       yes? show symbol t_z  
              T_Z = "14-JAN-1980"
       yes? plot i[i=1:10]
       yes? label 4,5,0,0,0.12 ($t_z)

 Hope This Helps

 With  Regards 

 Jaison 


On Mon, 3 Jan 2005, Steve Knox wrote:

> Good day,
> 
> I'm trying to read Netcdf files with ferret.
> Is there a way for Ferret to return, _as a variable_, the value of the 
> time _origin _of a netcdf  file?
> 
> The Netcdf files use the COARDS conventions:
>         int time(time) ;
>                 time:long_name = "Time" ;
>                 time:units = "days since 1895-01-01" ;
>                 time:time_step = "monthly" ;
> but in general the time units will vary so I don't know before running 
> my Ferret script what the time
> origin is, unless I write a separate script to parse the header info and 
> the value of time(0) from the
> Netcdf file. I'd like to avoid having to do that and just let Ferret 
> return "T0".
> 
> Thanks!
> 
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>         int time(time) ;
>                 time:long_name = "Time" ;
>                 time:units = "days since 1895-01-01" ;
>                 time:time_step = "monthly" ;
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> 

-- 
___________________________________________________

    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
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