| Re: experience with idl_grib package? [message #60224] |
Mon, 12 May 2008 08:15  |
wgallery
Messages: 32
Registered: December 1998
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Member |
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On May 8, 2:45 pm, sarale <sara.le...@gmail.com> wrote:
> Dear group users,
> I am rather new to IDL and completely new to the GRIB data format. I
> have tried to figure out how to read GRIB data into IDL and have found
> several packages on the web, seemingly all based on the rather old
> wgrib c programme. The latest package I found at ITTs webpage by Andy
> Pursch (http://www.ittvis.com/codebank/search.asp?FID=488), and it was
> easy to install and seems to be running fine. My problem, however, is
> that the documentation is quite poor and I cannot understand the
> obejct structure created. For example, I cannot see how to identify
> which parameter is in each "record", or what time of day it
> represents. Also, I work with ECMWF data which apparently use
> different parameter codes than the official WMO. Can anybody help with
> some good advice on how to advance?
> Yours sincerly,
> Sara.
Sara,
I use the NCAR Command Language (ncl) package from NCAR (http://
www.ncl.ucar.edu/overview.shtml) to convert grib files to NetCDF
format. I find NetCDF files much easier to use, with good support in
IDL. After converting to NetCDF you can use ncdump (http://
www.unidata.ucar.edu/software/netcdf/docs/ncdump-man-1.html) to get a
summary of the file contents or use David Fanning new IDL NetCDF file
browser (http://www.dfanning.com/fileio_tips/ncdf_browser.html) to
view the contents.
Note that the resulting NetCDF file will be two or three times larger
than the grib file.
ncl is available for most platforms, including Linux and Window
(cygwin). The two ncl programs you want to use are:
1: ncl_filedump: like ncdump, dumps a summary of the grib file
2: ncl_convert2nc: converts a grib (grib1 or grib2) file to NetCDF
format.
I have used ncl_convert2nc on ECMWF files with good results.
Good luck,
Bill Gallery
Atmospheric and Environmental Research, Inc.
Lexington, MA
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