Using Ferret with a icosahedral grid.

[Glenn Carver <Glenn.Carver@xxxxxxxxxxxxxxxx>]

I hate to mail the list so soon after my last message but I need some
advice from experienced Ferret users.

I want to use Ferret to visualise results from a stratospheric model. The
complication is that this model uses a hexagonal-icosahedral grid which is
not regular in latitude and longitude. The output goes to a netCDF file
which Ferret reads fine.

The difficulty is that the model nodes are numbered according to the grid
square number (or 'face' number) and we use a lookup array for the latitude
and longitude position e.g.
  TEMP(iface,ilevel,itime) would have a lat./long. coordinate of
LAT(iface), LONG(iface) and this is how the data is stored in the netCDF
file. LAT and LONG are invariant coordinate variables in the netCDF file.
Worst still the coordinates are not stored in the order you might naturally
expect for graphics. That is, we don't start from 90N,0E moving east and
south through the grid. For computational reasons the coords are ordered
such as you cannot rely on consecutive nodes being adjacent as ordered in
the variable arrays.

So Ferret doesn't see the variables on a lat-long grid but an abstract one.
At the moment, I can't quite see how to use Ferret to produce lat-long
plots of the main model variables.  My first thought was to regrid the data
but Ferret only appears to allow regridding of variables when the same no.
of axes are involved; unlike my case where I want to go from the single
axes (iFACE) to two axes (lat/long).

An obvious option would be to interpolate the data in the model before
writing to netCDF. However, as these files are the main model output, we'd
prefer not to do this.

Any suggestions on how to proceed would be very welcome.

    Glenn


-----------------------------------------------------------------------
Dr. Glenn Carver, Senior Research Associate    Phone: +44 (1223) 336524
Centre for Atmospheric Science,                Fax:   +44 (1223) 336473
Cambridge University, Chemistry Dept.,    Glenn.Carver@atm.ch.cam.ac.uk
Lensfield Road, Cambridge, CB2 1EW, UK    www.atm.ch.cam.ac.uk/~glenn/

         "Genius is one percent inspiration and ninety nine
          percent perspiration"   Thomas Edison.
_______________________________________________________________________