definition and use of W Longitude axis

[Emilio Mayorga <emiliom@xxxxxxxxxxxxxxxx>]

I've had some problems with the definition and use of West Longitudes
since I started using Ferret. I assign negative values to the W
longitude axis variable in my netcdf files. These sometimes create
errors in Ferret.

For instance, in the GUI I have to switch the Longitude option to use
x-index instead, otherwise I only get error messages like this one:

 **ERROR: illegal limits: PRECIP is not in the range X=65W
          Axis extremes are X=80W(-80):45W(-45)

In the command-line Ferret, I also encounter this problem sometimes,
such as the following, where the first line works fine and the second
results in the error message:

yes? shade/t=0:83/y=20S:6N precip[x=-65]
yes? shade/t=0:83/y=20S:6N precip[x=65W]
 **ERROR: illegal limits: PRECIP is not in the range X=65W
          Axis extremes are X=80W(-80):45W(-45)

Lastly (as another illustration), I just noticed that for these
variables that I've defined with negative values for W lon, using a
region specifier such as x=290E will result in an error message when
plotting variables (all my variables are defined in the window 80W to
55W, 2S to 6N).

* Does anyone know what's going on? Should I switch to using positive
values for W longitude in the netcdf longitude coordinate variables --
that is, will that option result in fewer errors and inconsistencies?

I appreciate any help on this.

Emilio Mayorga
________________________________________________________________
University of Washington	
School of Oceanography			emiliom@u.washington.edu
Box 357940				ph. (206) 543-5334
Seattle, WA  98195-7940	  USA		FAX (206) 685-3351
http://boto.ocean.washington.edu/staff_pages/emilio