20001221: inquiry from a new user

>From: "Tang, Youhua" <address@hidden>
>Organization: UCAR/Unidata
>Keywords: 200012211501.eBLF1Ho12598

>Dear Sir:
>
>I am a very new user of GEMPAK and just install GEMPAK according to the
>instruction.  However, I did not know how to start using it even if I
>searched your website. For example, after I convert a GRIB file to
>GEMPAK format by the decoder provided by GEMPAK, I did not know how to
>visualize the .gem file. I tried to load the file onto GARP, but I can
>not find a menu by which I  can load the .gem file. I also tried to use
>gdplot by setting gdfile=my.gem, but it did not work. Anyway, I need
>some instructions about how to operate GEMPAK to load my data and
>visulize it.
>
>By the way, could you tell me where I can download globe surface
>observation data. Another question is how can I convert gempak format
>to other format, such as ASCII data. The decoders that GEMPAK provide
>are only for converting other format to gempak.
>
>Thank you
>
>Youhua Tang
>


Yoshua,

A good starting point is teh GEMPAK tutorial at:
http://www.unidata.ucar.edu/packages/gempak/tutorial

as well as the online documentation for each program and the PDF format
user guide under $NAWIPS/doc 
(and http://www.unidata.ucar.edu/packages/gempak/tutorial/manual)

If you have decoded GRIB data using dcgrib, dcgrib2 or nagrib to
a file calles my.gem, then that will be the name of the file you specify
for gdfile. I don't know why your gdplot display failed. Please send
me the values you are using for the required parameters. 

Here is a simple example of plotting 500 mb height contours from
a grid file:

% source $NAWIPS/Gemenviron

% gdcntr
 GDATTIM  = f000
 GLEVEL   = 500
 GVCORD   = pres
 GFUNC    = hght
 GDFILE   = 2000122112_eta211.gem
 CINT     = 60
 LINE     = 6/1/1
 MAP      = 1/1/1
 TITLE    = 1
 DEVICE   = xw
 PROJ     = lcc
 GAREA    = uslcc
 CLEAR    = yes
 PANEL    = 0
 TEXT     = 1
 SCALE    = 0
 LATLON   = 0
 CTYPE    = c
 SKIP     = 
 GEMPAK-GDCNTR>run

 GEMPAK-GDCNTR>exit

% gpend


In the above, the data file is called 2000122112_eta211.gem,
This will use the xw (X window) device (you must have your DISPLAY
environmental variable set). This will plot the 0 hour forecast of
the parameter HGHT on the 500 MB level.


You can see what fields are in a grid file using the "gdinfo" program.
Set the GLEVEL, GVCORD, GFUNC, GDATTIM to "ALL" to see all the fields in a file.


You can list the data for a particular grid using the "gdlist" program.

In every GEMPAK program, you can type "help gdcntr" etc for help on running
the gdcntr program, or "help gdattim" to see information on the GDATTIM 
variable.

In general, looking at gridded data in ascii format isn't very pleasing
since there is not a convenient way of displaying so many values.

There are other programs such as gribtonc (in the
anonymous ftp on ftp.unidata.ucar.edu under pub/decoders/decoders.tar.Z
that decode GRIB to NetCDF for instance.

Garp uses the $GARPHOME/config/Garp_defaults file to define the locations
for different types of data sets. The data sets should follow the naming 
conventions
used in the defaults file so that the GUI can locate the files. Garp has an
online html format help document under $GARPHOME/html. You can define your
browser (netscape, hotjava, ie etc.) in the $GARPHOME/config/Garp_defaults file.
By default, it is set to use netscape which should be in your path.

If you have specific problems with a GEMPAK program, please send me the
output of the program and all the parameter settings you are using.


Steve Chiswell
Unidata User Support