Re: status of nj22 WRT netCDF-4

Thanks John, though I'm now a bit confused I think.. ;-(

 nj22 implements the CDM data access layer
 the CDM data access layer is the same as the NetCDF-4 data model

Not true (yet):
nj22 implements NetCDF-4 Details: When the NetCDF-4 file format is finalized (waiting on HDF5-1.8), then nj22 will be able to read NetCDF-4. It will not immediately be able to write, and depending on how complicated things are (HDF5 is pretty complicated, esp compared to netcdf-3), it may end up only only writing a subset of netcdf-4. I would guess eventually it will write the whole thing, but that will depend on funding. There has never been an independent library that writes (or reads) HDF5, so we are wary of promising what hasnt been done before. We have prototyped HDF5 reading enough to know we can do that.

Hang-on, I thought that the HDF5 stuff was required to implement the new features in the netCDF-4 data model? Certainly that is how I understand things to be in the netCDF-4.0-alpha libraries -- to use 'netCDF-4 format' requires HDF5-1.8 (or 1.7.52), though of course things may be different in the nj22 world. What storage model does nj22 use to implement the CDM data access layer if not HDF5? Does nj22 extend the netCDF-3 file format to support eg multiple unlimited dimensions etc? or does it not support all of the netCDF-4 data model? (is the CDM data access layer a subset of the netCDF-4 data model?)

What am I missing?


Simon Wood

Simon Wood                                  Meteorology & Remote Sensing
Scientific Programmer                                               NIWA        

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