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Re: [ferret_users] Compressed ferret output incompatibe with netcdf java apps

I experimented and found that if the file is written in Ferret using the qualifier /SHUFFLE=1 and deflation, then it seems to work correctly, at least in Panoply.

In looking at some the netCDF documentation, I find this page that discusses the netcdf-java tools.

It says that shuffle=true is the default for nccopy. So that seems to be why running the file through nccopy causes it to work in the java-netCDF apps, and this may be what's meant by the "filter type =0" setting in the error message. Does this seem like a good solution to you Russ?


On 1/28/2016 10:52 PM, Russ Fiedler wrote:


This is possibly a problem with netcdf java rather than ferret but anyway...

If we make a variable and save it in compressed netcdf4 format it appears that java based netcdf software han't handle it.


yes? let v=i[i=1:20]+j[j=1:20]
yes? save/file=cmp.nc/ncformat=netcdf4/def v ! compressed (actually it's larger but just an example)
yes? save/file=uncmp.nc/ncformat=netcdf4 v      ! uncompressed

Now loading up in Panopoly (and another of our in house apps which is where we spotted the problem).When we try to operate on v we get a message about an an unknown filter type being zero for the compressed version

java.lang.RuntimeException: Unknown filter type=0
at ucar.nc2.iosp.hdf5.H5tiledLayoutBB$DataChunk.getByteBuffer(H5tiledLayoutBB.java:198)

The uncompressed version is fine since there are no filters being applied.

Now, here's where it gets weird. If nccopy is used to convert the two files to compressed netcdf4 style the originally compressed file is still giving Panopoly grief but the newly compress file is handled just fine!

xwing-hf% nccopy -k 3 -d 1 cmp.nc cmp_ncopy.nc          ! Still no good
xwing-hf% nccopy -k 3 -d 1 uncmp.nc uncmp_ncopy.nc ! compressed file is fine!!!

Any clues? A known issue?

Occurs for V6.95, V6.96 and earlier by the looks.


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