[pyngl-talk] how to use the new MRMS grib codetable

[Root, Benjamin]

That's great to hear! I would just like to point out one particular
pitfall that is tripping me up. The MRMS data from NCEP's LDM feed are
all gzipped (yeah, I know, craziness...). Both PyNIO and pygrib expect a
filepath object to a grib2 file as opposed to a file-like object. I have
dug down into PyNIO's Grib2 reader, and I see that this requirement
seems to be fairly artificial, as the relevant C-code just simply opens
up a standard C file object.

matplotlib has code that can produce a C file object from a Python
file-like object that you guys can use. We use it to interface with
libfreetype. It originally came from Numpy so that that library could
interface with datafile readers that expect a FILE pointer.

https://github.com/matplotlib/matplotlib/blob/master/src/file_compat.h

I don't know yet if this would work for file-like objects such as
objects from a TarFile or GzipFile, but it might be a step forward. This
code works on Windows, Linux, and Macs, and is py3k compatible.

Cheers!
Ben Root

On 07/02/2015 03:51 PM, David Brown wrote:
> Hi Ben,
> Coincidentally, there is someone also asking about MRMS data support
> for NCL. I am not sure at this point whether it is just a matter of
> creating the right tables or whether some source code changes will be
> needed as well. But given the amount of interest I will look into this
> now.
>  -dave
>
> On Thu, Jul 2, 2015 at 1:25 PM, Root, Benjamin <broot at aer.com> wrote:
>> ...unless one is having difficulties compiling the new wgrib2 package
>> (grrr...).
>>
>> I guess what I am trying to get at is (1) is there a utility that can
>> help convert a wgrib2 codetable into a form recognizable by the ecmwf
>> grib api and (2) how does one get custom codetables recognized by PyNIO?
>>
>> Ben Root
>>
>> On 07/02/2015 03:12 PM, David Brown wrote:
>>> Hi Ben and Nick,
>>> Thanks Nick for the pointer to MMM-Py. From there I can get to
>>> information about the MRMS data, plus some sample data sets.
>>> The key point, relative to PyNIO from this documentation is the following:
>>>
>>> "The GRIB2 IDs used by MRMS are not officially sanctioned at this
>>> time.  Instead, MRMS uses a local discipline number (209) and it’s own
>>> set of category and parameter values.  This means that most widely
>>> available GRIB2 decoders will require customization."
>>>
>>> MMM-Py relies on a customized version of wgrib2 to do the actual
>>> reading. To make this data readable by PyNIO it will probably be
>>> easiest to work from the modified wgrib2 code. This may be pretty
>>> simple, but it will take a bit of research.
>>>
>>> So for now, I would agree that MMM-Py is probably the best bet.
>>>  -dave
>>>
>>>
>>>
>>>
>>> On Thu, Jul 2, 2015 at 12:14 PM, Nick Guy <Nick.Guy at uwyo.edu> wrote:
>>>> Ben,
>>>>
>>>> Not sure what your use is, but this package works to read in MRMS and is
>>>> pretty nice to work with:
>>>> https://github.com/nasa/MMM-Py
>>>>
>>>> Nick
>>>>
>>>> On Jul 2, 2015, at 12:00 PM, pyngl-talk-request at ucar.edu wrote:
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>>>> ----------------------------------------------------------------------
>>>>
>>>> Message: 1
>>>> Date: Thu, 2 Jul 2015 16:43:27 +0000
>>>> From: "Root, Benjamin" <broot at aer.com>
>>>> Subject: [pyngl-talk] how to use the new MRMS grib codetable
>>>> To: "pyngl-talk at ucar.edu" <pyngl-talk at ucar.edu>
>>>> Message-ID:
>>>> <47A91F4E74556440877A9E87A31CE9D20952D420 at VRSKUTMB2.veriskdom.com>
>>>> Content-Type: text/plain; charset="us-ascii"
>>>>
>>>> I am working with the (somewhat) new MRMS datafeed from NCEP. I managed
>>>> to find a codetable for it in the wgrib2 source code:
>>>> http://www.ftp.cpc.ncep.noaa.gov/wd51we/wgrib2/user_tables/MRMS_usertable,
>>>> but I am stuck in trying to get PyNIO to utilize it. I am not even sure
>>>> if it is in the right format for use in PyNIO.
>>>>
>>>> Any tips would be appreciated.
>>>>
>>>> Cheers!
>>>> Ben Root
>>>>
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