README.fdf
P.Bruehl 8/12/96

Defining FDF's:
--------------

The FDF (Function Definition File) is a simple text file which defines
a GFUNC or GVECT specification.  You can easily create FDF's for your
favorite simple or complex diagnostic functions.  All the FDF's for
plan view graphics are stored in the $(GARPHOME)/fdf/scalar and 
$(GARPHOME)/fdf/vector directories.  Cross section FDFs are stored
in the $(GARPHOME)/fdf/xsscalar and $(GARPHOME)/fdf/xsvector 
directories.  These directories are defined in the config/Garp_defaults
file.   

The FDF format allows you to specify a simple GFUNC or GVECT, or you
can make a complete specification, including most of the GEMPAK 
variables.  For a sample FDF, please see the $(GARPHOME)/fdf/ 
directories.  For a blank FDF template, please see the file
valid_fdf_keys, in the $(GARPHOME)/fdf/ directory, and here, in this
directory.

Lines beginning with a "!" are comments.  The required variables are 
indicated.  The optional variables may be specified, or left blank.
GEMPAK will use default values for blank variables.

The file name you choose for the FDF will be the name that appears in 
the "Scalar Field" or "Vector Field" scroll window in the Gridded Data 
or Cross Section selection window.  The addition of FDF's is dynamic, 
so you can add new FDF's to GARP at any time.

To create a new FDF, I suggest that you copy an existing FDF, and make
the necessary changes to the required and/or optional variables.  You 
must also choose an appropriate file name. You must put the file in the 
appropriate directory ($GARPHOME/fdf/scalar, $GARPHOME/fdf/vector,
$GARPHOME/fdf/xsscalar $GARPHOME/fdf/xsvector), and it is ready to be 
used.  Sometimes, functions can be used in both plan projection and
cross section graphics.  If this is the case, I recomment that you
put the FDF in the $GARPHOME/fdf/scalar directory, and create a link
to the $GARPHOME/fdf/xsscalar directory.   For example, if I create
an FDF called "Temp_K" and placed it in the $GARPHOME/fdf/scalar
directory, I can use the following command to create a link in the
$GARPHOME/dfd/xsscalar directory:

  ln -s $GARPHOME/fdf/scalar/Temp_K $GARPHOME/fdf/xsscalar/Temp_K

You can contribute any FDF's you have written to the directory 
contrib/fdf/ on the SAC FTP server.  As FDF's are written at COMET, 
they will be added to this directory as well (and to subsequent releases
of GARP).  The only requirements for a contributed FDF are that you 
include your name in a comment line, and that you check to be sure no 
other FDF on the contrib/fdf/ directory has the same name.  (If there 
is an FDF of the same name, make a simple change to your file name).

__________________________________________________________________
Peggy Bruehl                     National SAC Coordinator - NWS
peggy@comet.ucar.edu             COMET/UCAR PO Box 3000
(303) 497-8356                   Boulder, CO 80307-3000
SOO/SAC Home Page: 
http://www.comet.ucar.edu/pub_html/sac_html/index.html
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