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20020506: Unidata gribdec.tar.Z bundle (cont.)

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  • Subject: 20020506: Unidata gribdec.tar.Z bundle (cont.)
  • Date: Mon, 06 May 2002 10:51:32 -0600
>From: "Hoeth, Brian" <address@hidden>
>Organization: JSFC
>Keywords: 200205011845.g41IjMa25331 McIDAS gribdec.tar.Z

Brian,

>Thanks for all your help!!  I have picked up the new software and it seems
>to be decoding the 8km data just fine. 

Sounds promising :-)

>Now it's choking on a few messages in some of the ETA 12km data I've been
>experimenting with.  I've been debugging through the code and I've found
>where the decoder is choking.  It seems to be in the grib_dec_is routine.

Do you have an example file I can use for debugging.  A URL to a dataset
would also work.

>The return value is -2 which means that the IS length appears too long.  I
>noticed that the grib.h file has the GB_MAX_MSG_LEN parameter that is being
>used to compare the length of the IS with.  I diff'd your version of grib.h
>with what's currently in xcd7.8/src and I see that you increased this
>parameter from 200000 to 400000.  Is there any reason why you chose 400000
>other than it was "bigger"?  

No, not really.  The code was written by a Fortran programmer programming
in C.  There should not be any hardwired lengths of arrays, only checks
for reasonableness of the size of the sections of grib messages.  This
is a major change that needs to be made in the grib decoding in McIDAS.

>Anyways, I went ahead and increased the length of this parameter (and
>GB_MAX_DATA_PTS while I was at it) to 600000 and the grib decoder still
>didn't work?

Interesting.

>So, I did some more digging and found that I needed to
>increase the MAXGRIDPT value in gridparm.inc also.  So, I increased this
>value to 600000 also and everything worked out great!

Hmm... gridparm.inc is mainly used in McIDAS display/analysis routines,
not in any XCD routine.  I would not have expected that a change in
gridparm.inc would result in the decoder working for larger grib messages.
Now, I would have expected a change in grib.h to make a difference.

>Will increasing GB_MAX_MSG_LEN, GB_MAX_DATA_PTS, and MAXGRIDPT to 600000
>have any ill affects to any of the McIDAS code?  Seems to display fine with
>GRDDISP? 

Just remember that as you increase MAXGRIDPT, the size of GRID McIDAS analysis
routines grow proportionately.

Tom

>From address@hidden Mon May  6 10:57:33 2002
>Subject: RE: 20020506: Unidata gribdec.tar.Z bundle (cont.) 

Here's info on the 12km ETA data (use the second link!):

> > To anyone who wants to access or has been accessing the Operational
> > four-per-day Meso Eta 12-km AWIPS grid (#218) in GRIB from
> > ftp.ncep.noaa.gov/pub/emc/eta12.tHHz (HH=00,06,12,18), please note
> > that these files are now available at the new NCEP ftp server at
> >
> > ftp://ftpprd.ncep.noaa.gov/pub/data/nccf/com/eta/prod/
> >
> > in directories/files named eta.yyyymmdd/eta.thhz.awip12ff.tm00,
> > where yyyy=year, mm=month, dd=day, hh=cycle, ff=forecast hour.

Thanks!