RE: [ferret_users] Picking the time corresponding to maximum value of a variable from an nc file

[Sandhya K G <sandhyakg@xxxxxxxxxxxxx>]

Dear Hein Zelle,

Thanks for the suggestion.
I have done exactly what you said, though I did not understand why you are doing 
! limit to one point only
?set region /i=100/j=50

I paste below the result of the commands.

yes? sh d
     currently SET data sets:
    1> ./Hs_timeseries.nc  (default)
 name     title                             I         J         K         L
 HS       HS_CM/100                        ...       ...       ...       1:2919

yes? sh gr hs
    GRID GGE1
 name       axis              # pts   start                end
 normal    X
 normal    Y
 normal    Z
 TAXIS     TIME              2919 r   01-JAN-2009 02:57    31-DEC-2009 20:57

yes? let zero_at_max=hs[t=@max]-hs
yes? let maxtval=zero_at_max[t=@loc:0.0] 
yes? set region/i=100/j=50
yes? let dummy=t[gt=hs,t=`maxtval`]
 !-> DEFINE VARIABLE dummy=t[gt=hs,t=954690]
yes? let tstring=`dummy,return=tend`
 !-> DEFINE VARIABLE tstring=12-DEC-2009 17:57:00
 **ERROR: command syntax: 12-DEC-2009 17:57:00
          illegal character: :

The time corresponding to the maximum of Hs is actually 12-DEC-2009 17:57:00 (I checked this). But it seems that I can't list this time using ferret. I don't understand why a command syntax error should come here.

yes? list tstring
 **ERROR: variable unknown or not in data set: TSTRING

Though my purpose is served temporarily, I am curious to know the cause of the error. Any inputs?


Regards,
********************************************************************************************************
Sandhya K G
Scientist
INDIAN NATIONAL CENTRE FOR OCEAN INFORMATION SERVICES
(Ministry of Earth Sciences, Govt. of India)
"Ocean Valley", Pragathi Nagar (B.O), Nizampet (S.O), HYDERABAD-500 090.
Ph : +91-40-23886036 (Work : 0900-1730hrs)
       +91-8019596800 (Mobile)
FAX : + 91-40-23892910
url: http://www.incois.gov.in
********************************************************************************************************
________________________________________
From: owner-ferret_users@xxxxxxxx [owner-ferret_users@xxxxxxxx] On Behalf Of Hein Zelle [hein.zelle@xxxxxxxxxxxxx]
Sent: Wednesday, January 23, 2013 4:01 PM
To: Ferret users mailing list
Subject: Re: [ferret_users] Picking the time corresponding to maximum value of a variable from an nc file

HI Sandhya,

> yes? list hs[l=1:2919@loc:2.2]
>              VARIABLE : TIME of 2.2 in HS_CM/100 (HOURS)
>              FILENAME : Hs_timeseries.nc
>              TIME     : 01-JAN-2009 01:27 to 31-DEC-2009 22:27 (location of 2.2)
>           954690.
>
> yes? list t[gt=hs]

Once you have the index, you can print the time value (or put it in a
variable) with

let mytimestring = `t[gt=hs,l=954690],return=tstart`

You can't use recursive backticks, so I usually do this in a few
steps.  I define a new variable which is zero at the maximum so you
can use a fixed value (0.0) for @loc.

let zero_at_max = myvar[t=@max] - myvar
let maxtval = zero_at_max[t=@loc:0.0]

! limit to one point only
set region /i=100/j=50

let dummy = t[gt=myvar,t=`maxtval`]
let tstring = `dummy,return=tend`


Note that my example dataset insists on returning the 't' value with
@loc, not the 'l' index.  This is why I used t=`maxtval` instead of
l= .


Kind regards,
     Hein Zelle


--

Dr. Hein Zelle
Senior consultant meteorology & oceanography

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