GRIB1 quasi/thin grids

[Robb Kambic]

the grib-5.1.02.jar is a new jar with the changes.


On Wed, 28 Feb 2007, Don Murray wrote:

> 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. 

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Robb Kambic        			   Unidata Program Center
Software Engineer III			   Univ. Corp for Atmospheric Research
rkambic at unidata.ucar.edu		   WWW: http://www.unidata.ucar.edu/
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