[Met_help] Points of clarification for data conversion/usage in MODE

John Halley Gotway johnhg at ucar.edu
Fri Mar 12 15:36:46 MST 2010


Yeah, polar stereographic is fine.  Actually, *northern* polar stereographic is currently supported in MET - not southern yet for some reason.  You just need to figure out what to put in the NetCDF
header to define it.  If you can get your hands on a GRIB file, you could run it through the copygb tool to interpolate it a polar stereographic projection.  Then run it through the PCP-Combine tool
(the operation you do with PCP-Combine doesn't really matter).  And then look at the NetCDF output file.

Just let me know if you get stuck anywhere.


Matthew Souders wrote:
> Boy...it seems like no matter what alley I drive down, there's an acme anvil
> rigged to fall on my head.  I should change my last name to Coyote.
> In all seriousness, I do appreciate you going through the various tools and
> ideas with me...at this point...I am thinking it would be a less painful
> task to change map projection of my data BEFORE I try to create the netCDF
> than it would be to convert it later.  I al going to have to write some kind
> of MATLAB script to convert every piece of data I have to a projection I can
> use...at which point I can then convert to netCDF and read the thing into
> MODE, I assume?  Will MODE recognize a netCDF file in a polar stereographic
> projection?
> On 3/12/10, John Halley Gotway <johnhg at ucar.edu> wrote:
>> Matt,
>> Here's a link regarding that:
>> http://www.unidata.ucar.edu/software/netcdf/docs/faq.html#grib
>> Converting GRIB to NetCDF is pretty easy.  The tool "ncl_convert2nc" does
>> it for you.  Going the other way is much more difficult.  And really, I've
>> never done it before.
>> John
>> Matthew Souders wrote:
>>> Unfortunately, I have not used NCL before.  Given my time limmitations in
>>> completely this analysis, I am thinking that will be
>> impractical.  regular
>>> lat/lon doesn't really work because I have to split the grid in half and
>>> then track objects that straddle the divide somehow...which causes lots
>> of
>>> problems.  There is software out there that can convert a netCDF to a
>> GRIB,
>>> isn't there?  I seem to recall that being out there in some form.
>>> On 3/12/10, John Halley Gotway <johnhg at ucar.edu> wrote:
>>>> Matt,
>>>> There is no general tool for regridding NetCDF files from one grid to
>>>> another.  You may be able to write an NCL (NCAR Command Language) script
>> to
>>>> do so, but there's a learning curve if you haven't
>>>> used NCL before.
>>>> John
>>>> Matthew Souders wrote:
>>>>> One reason I started down the long and scary road of trying to create
>>>> GRIB
>>>>> files was to gain access to the copygb utility in order to convert my
>>>>> regular lat/lon grid to polar stereographic without too much
>>>> hardship.  Is
>>>>> there a way to convert a netCDF file in regular lat/lon to polar
>>>>> stereographic simply?
>>>>> It does seem like using netCDF is a better way to go...I believe even
>>>>> (my main dta interface tool) has a netCDF writer...it definitely has
>> (and
>>>> I
>>>>> use) a netCDF reader.  But I need to figure out how to change map
>>>>> projections and how exactly to set up the netCDF file so that MODE can
>>>>> understand it.
>>>>> I will take a look at the output from P2P_Combine...that file
>> definitely
>>>>> created successfully when I ran the test script...I can see it in my
>>>>> directory.
>>>>> On 3/12/10, John Halley Gotway <johnhg at ucar.edu> wrote:
>>>>>> Matt,
>>>>>> Creating a GRIB file is a rather ambitious task I have never actually
>>>> done
>>>>>> myself.  If I were in your position, I'd actually reformat your binary
>>>> data
>>>>>> into a NetCDF file that looks like the output of
>>>>>> the PCP-Combine tool.  MODE can read either GRIB data or the NetCDF
>>>> output
>>>>>> of PCP-Combine.  There are a lot more utilities out there for writing
>>>> NetCDF
>>>>>> files than there are for writing GRIB files.
>>>>>> Use the "ncdump" utility to view the NetCDF output from PCP-Combine in
>>>> the
>>>>>> "METv2.0/out/pcp_combine" directory.  These files are created when you
>>>> run
>>>>>> the test script included with MET.  And just
>>>>>> mimick the file structure with your data.
>>>>>> If you choose to go that route, you'll probably need some help
>> choosing
>>>> the
>>>>>> variable name and setting up the grid definition information in NetCDF
>>>>>> header.  We're working on expanding our support for
>>>>>> NetCDF files for the next release of MET.  They're a lot easier to
>> work
>>>>>> with than GRIB files are.
>>>>>> Let me know how you plan to proceed and what other questions you have.
>>>>>> Thanks,
>>>>>> John
>>>>>> Matthew Souders wrote:
>>>>>>> Hello John,
>>>>>>> This is Matthew Souders (Stony Brook University) - I apologize for
>>>> taking
>>>>>> up
>>>>>>> a bit more of your time, but I am running into some trouble getting
>>>> data
>>>>>>> read into MODE for which I thought you might have a solution on hand
>> to
>>>>>>> help.  My basic data is a single variable on a 2.5 by 2.5 degree
>>>> regular
>>>>>>> lat/lon grid in fortran direct access BINARY format.  I have been
>>>> trying
>>>>>> to
>>>>>>> get it intelligibly read into GRIB format (the form MODE needs) for a
>>>>>> month
>>>>>>> now using Wesley Ebusizaki's gribw utility; however, you need a
>> rather
>>>>>>> significant background in C scripting to rewrite his basic code and
>>>> make
>>>>>>> proper use of the PDS file writer.  As I understand it...MODE needs
>>>> this
>>>>>> PDS
>>>>>>> file to operate properly.  I can create a GRIB using the default PDS
>>>>>> file,
>>>>>>> but that doesn't accurately describe the data in the GRIB.
>>>>>>> I tried e-mail Wesley on this matter but he is understandably
>> extremely
>>>>>> busy
>>>>>>> and limits support to installation and debugging issues.  He
>> basically
>>>>>> just
>>>>>>> directed me to the GRIB standard release.  I was wondering if you had
>>>> any
>>>>>>> experience getting binary data read into MODE or if you knew someone
>>>> who
>>>>>>> might be able to help?
>>>>>>> I also would like to know how exactly the MODE tool uses the PDS
>>>> file?  I
>>>>>>> ask because I am trying to figure out how picky it is w/r/t what is
>> in
>>>>>> the
>>>>>>> PDS file vs. what is in the actual GRIB file.
>>>>>>> Thanks in advance for your time.
>>>>>>> Matt Souders.

More information about the Met_help mailing list