[ferret_users] Two interpolation syntax questions

[Steve Guimond <guimond@xxxxxxxxxxxxx>]

Dear Ferreters:
   I have two separate, but related questions.  I have latitudes,
longitudes and times for the 
positions of several tropical cyclones and need to co-locate with some
satellite data.  
Basically, just need to do a simple interpolation to find the position of 
the storm at satellite 
overpass.  So, the positions of the storm are at 20.50,53.50 at 0000Z and 
21.34,52.10 at 
0600Z and the satellite overpass is at 0325Z.  
   Data looks like:

day     i=1:48
time    i=1:48
lat       i=1:48
lon      i=1:48

   I wanted to find the appropriate "i" position in the array that 0325Z
was between and then 
apply my own interpolation calculations, but found this difficult.  In
fortran I would code:

do i=1,48
if ( 0325 .gt. time(i) .and. 0325 .lt. time(i+1) ) then
complete interpolation
endif
enddo

I tried this in ferret by saying:

repeat/range=1:48:1/name=a (if 20 eq day[i=`a`] and 0325 gt time[i=`a`]
and 0325 lt 
time[i=`a`+1] then complete interpolation)

I tried various sequences, but could not get the equivalent of my fortran 
code in ferret to 
work.  
     Additionally, I tried using the @weq transformation as:

let test = lat*time[x=@weq:1030]      !trying a different time here
let nlat = test[x=1:48@sum]

This worked for the first time in the array between 0000Z and 0600Z, but
did not produce a 
field of coefficients for the rest of the times that I needed.  This is
what I got from listing test 
and time together...
       time    test
1/1: 600.    3.173
2/2:1200.   8.027
3/3:1800.   ....
4/4:      0.   ....
5/5: 600.     ....
6/6:1200.   ....
etc.......

why are there not coefficients for the rest of the times at 1030?

Can anyone help to clear up (1) how to cycle through data element by
element like fortran 
for the statement above and (2) how to get coefficients for all the times 
and not just the first 
instance of 1030 like I showed above?


Many thanks...

Steve Guimond



*****************************************
Stephen R. Guimond
Graduate Research Assistant
Center for Ocean-Atmospheric Prediction Studies 
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