GRIB1 quasi/thin grids

[Don Murray]

Hi Robb/John-

Good new! When there's a new nc2.2.jar that I can use to test
this in the IDV, let me know and I'll bang on it.

Don

Robb Kambic wrote:
> 
> Good news, the Grib1 quasi/thin grid work is done for the NCEP and the
> ECMWF grids. Now the challenge is how to implement it, since it involved
> an API change to the index.  Data offset was changed to the GDS offset in
> the grib file. I made the new grib1 data reading code to be able to use
> the old index data offset as well as a new index GDS offset. of course,
> if the old index data offset is given and it's a Quasi grid, then the grid
> doesn't get expanded. But for the motherlode case, in 7 days all the 
> indexes will be the new index type. The older grib1 data reading code will
> not be able to use the new index offset of the GDS. so the change has to 
> be a code change first, then the indexes can be updated later.
>    Another problem occurs in
> the nj22 code that checks the index versions before using the index. Maybe
> i could change the check to allow index version 3.0 and above. the
> motherlode indexes are currently version 3.0 and the new index version is
> 4.0.
> 
> If the nj22 change is made then the new code could be installed on the 
> lead machine without reindexing the whole repository. last time, i
> reindexed the lead machine, it took over 8 days and some of the new data 
> was lost since the cpu was tied up according to Tom.
> 
> 
> the new code is not ci but i plan on doing it later today unless there is
> some objections.
> 
> RObb...
> 
> 
>>
>> On Thu, 15 Feb 2007, Robb Kambic wrote:
>>
>>> the fix to make the GRIB1 quasi/thin grids work required an API 
>>> change in the grib1 index file.  instead of seeking to the data 
>>> section offset, i have to seek to the GDS offset to get the thin grid 
>>> info when a getData call is made. remember the GDS is before the data 
>>> section offset and there is no sure way to back up to the GDS 
>>> section.  since i didn't want to reindex all of motherlode again and 
>>> lead repository, i added code to decide if the offset was a GDS 
>>> offset or a data offset. the code is not full proof, should work in 
>>> the high 90's though. after all the indexes have been redone then the 
>>> code will work 100% and i can delete the extra code.  What do you 
>>> think...
>>>
>>> i'm still doing test on motherlode before ci the code. 

*************************************************************
Don Murray                               UCAR Unidata Program
dmurray at unidata.ucar.edu                        P.O. Box 3000
(303) 497-8628                              Boulder, CO 80307
http://www.unidata.ucar.edu/staff/donm
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