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Re: Problem opening GRIB dataset using netCDF-Java

Hi Robert:
On 9/18/2013 12:56 AM, Schmunk, Robert B. (GISS-611.0)[TRINNOVIM, LLC] wrote: 
John,

A Panoply user has been having trouble opening a GRIB dataset due to an 
exception thrown from somewhere inside the NJ library. The exception is caught 
and re-thrown by NetcdfFile.open(), but further tracing reveals something going 
on when Gri1IOSP tries to open the file.

java.io.IOException: java.lang.IllegalArgumentException: Attribute value cannot 
be null
        at ucar.nc2.NetcdfFile.open(NetcdfFile.java:425)
        at 
ucar.nc2.dataset.NetcdfDataset.openOrAcquireFile(NetcdfDataset.java:699)
        at ucar.nc2.dataset.NetcdfDataset.openDataset(NetcdfDataset.java:421)
        at ucar.nc2.dataset.NetcdfDataset.acquireDataset(NetcdfDataset.java:516)
        at ucar.nc2.dataset.NetcdfDataset.acquireDataset(NetcdfDataset.java:493)
        at gov.nasa.giss.netcdf.NcDataset.init(NcDataset.java:118)
         ... more
Caused by: java.lang.IllegalArgumentException: Attribute value cannot be null
        at ucar.nc2.Attribute.setStringValue(Attribute.java:508)
        at ucar.nc2.Attribute.<init>(Attribute.java:370)
        at ucar.nc2.grib.grib1.Grib1Iosp.addGroup(Grib1Iosp.java:338)
        at ucar.nc2.grib.grib1.Grib1Iosp.open(Grib1Iosp.java:160)
        at ucar.nc2.NetcdfFile.<init>(NetcdfFile.java:1521)
        at ucar.nc2.NetcdfFile.open(NetcdfFile.java:813)
        at ucar.nc2.NetcdfFile.open(NetcdfFile.java:422)
        ... 16 more

I'm at a loss as to what to tell the user, as there's no further info presented 
about what attribute it is that has a null value. It would be of some help if 
the exception would also report the name/key of the problem attribute.

A copy of the dataset is currently at
http://www.giss.nasa.gov/staff/rschmunk/data/20130917_153410_.grb
Im out of the country for another week so i cant check, but i fixed a similar problem in the 4.3.19 release. Lansing can tell you where that is if you want to try. 

Ill add a better error message when i get back.




BTW: I commented last March that I had been having since the start of the year with GRIB 
temporary files popping up in the same directory as the GRIB file rather than in the 
cache dir specified by DiskCache.setRootDirectory(). I thought this was "fixed" 
in 4.3.18 but that was mistaken. On further exploration today, I found that a deliberate 
change was made in 4.3.15, as described at
http://www.unidata.ucar.edu/software/thredds/current/netcdf-java/reference/Caching.html

However, although that webpage states that as of 4.3.15 one should use 
DiskCache2 class to deal with GRIB files, the section terminates before 
providing an example of the DiskCache2 options. I did find an example in the 
source code for the TestGribDiskCache class which gave me the help I needed.
apologies, ill update that web page. so you did figure out what you needed then? 

John