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19990920: combining gempak and grads

>From: Matt Fearon <address@hidden>
>Organization: Desert Research Institute
>Keywords: 199909202052.OAA24442

>Steve,
>
>I am performing some calculations in gempak and then
>displaying in grads.
>
>After obtaining the eta grib data via ftp, I am converting the
>grib to gempak grid format. Then I am performing some
>calculations using gempak programs.
>
>After performing calculations and having a single gempak
>grid file, I was wondering if there is a way to re-convert
>the gempak grid file back to grib? Supposedly I can then
>read the grib file into grads. Or a shorter way, if it is possilbe,
>may be to read the gempak grid file straight into grads w/o
>re-converting to grib?
>
>The reason I start in gempak is that I can perform certain
>calculations easier in gempak than in grads, but for the
>final product graphical display, in this case, I prefer grads.
>
>If you have any ideas, please let me know.
>Thank you,
>Matt Fearon
>address@hidden
>
>
>
>

Matt,
I do not have any way of converting a Gempak file back to grib.
In general, you would need some information for generating the
grib product that is not stored in the Gempak file when it is
decoded.

You could create a program to convert the Gempak file to the grads
format if you know the requirements there. Reading a gempak
grid file is generally straight forward when using the gemlib.a
library routines-

IN_BDTA  initiallizes the gempak interfaces
GD_OPNF  opens the gempak grid file
GD_NGRD  determines the number of grids in the file
GD_GGRD  returns a grid given its number in the file (eg from 1 to number of 
grids)
         returns the grid times, levels, vertical coordinate, parameter name,
         number of x,y gridpoints, the nagigation information and the grid 
array.

Once you have the gempak grid read in from the file, you can decide how to
output the grid into the grads file.

If you need help creating the stub to read the gempak grid, I can
create that for you. Let me know.

Steve Chiswell
Unidata User support



GD_GIDN  obtains the grid information (level, coordinate, parameter)