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Re: Extracting data along transects

On Apr 19,  3:55pm, Robert Newton wrote:
> Subject: Extracting data along transects
> I have model output, and I want to extract it along a transect
> which matches an ocean cruise.  The cruise, of course, does not
> run along a model grid (or even a particularly straight) line.
> I've translated the lat/lons of the cruise stations into i,j
> coordinates from the model domain.  Now  . . . is there a way
> to use ferret to extract the model output along a section that
> matches the cruise track?
> >-- End of excerpt from Robert Newton

Hi Robert,

	I have done this in the past, and unfortunately it is not the easiest
thing to do in ferret. Ferret assumes things are on a grid, and cruise tracks
never are.

	What I have done in the past is to use a combination of a ForTran (or
C) program and Ferret. I can't be overly explicit because it somewhat depends
on your particular circumstances, but I will outline it for you.

1) I set up a .jnl file that extracts the data I want along the cruise path and
output this to an ascii file. E.g.

list/nohead/file="track.dat" u[position1], v[position1]
list/append/nohead/file="track.dat" u[position2], v[position2]
(where position[1,2....n] are the locations along the cruise track)

2) I create a NetCDF file with the x axis being the distance along the track,
you could also write out the lat and lon so that you have that and can use that
in the future for plotting.

3) I use a fortran program to insert the data I output from ferret into the
NetCDF file.

4) Then I use the data. Like I said, you could use the lat and lon in the
NetCDF file for later output.

Hope this helps, Mark


	      Mark Verschell (verschell@coaps.fsu.edu)
	      Center for Ocean and Atmospheric Prediction Studies
	      Florida State University
              2035 E. Paul Dirac Drive
              R.M. Johnson Bldg. - Suite 200
	      Tallahassee, FL  32306-3041
	      (904) 644-6532              (904) 644-4841 (fax)

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