Re: status of nj22 WRT netCDF-4

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

> True:
>  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?

thanks

Simon Wood

--
Simon Wood                                  Meteorology & Remote Sensing
Scientific Programmer                                               NIWA        
address@hidden                              http://www.niwa.co.nz

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