[netCDF #NRE-269426]: ncdump -x with netCDF4 files

Meg,

> Strange! That means our files are the netCDF-4 enhanced version, so I'm
> surprised anyone could get ncdump -x to work on them. I guess it will
> remain an unsolved mystery.

A possible explanation for the mystery is that your netCDF-4 files 
really don't use any features of the enhanced model, but aren't
marked as netCDF-4 classic model files.  A netCDF-4 classic model
file is just a netCDF-4 file with a special scalar integer attribute 
named "_nc3_strict" in the root group, which is tested to enforce
never adding any features of the enhanced netCCDF-4 data model to 
the file, so that it will always be readable using the netCDF-3 API.

Back in version 4.1.1, I don't think ncdump tested the file type, it
just printed whatever it could see through the API and displayed it
as NcML when the "-x" flag was used. But the ncdump code was never
modified to present the NcML representations for any of the netCDF-4
enhanced model features, partly because those representations were
still under development when netCDF 4.1.1 was released.

If your current netCDF files are really netCDF-4 files that don't 
use any enhanced data model features, then you could mark them as
netCDF-4 classic model files using the "nccopy" utility:

  nccopy -k "netCDF-4 classic model" foo4.nc foo4c.nc

to convert a netCDF-4 file to a netCDF-4 classic model file. That
would add the extra attribute (invisible through the netCDF API).
You could also do the same thing through the HDF5 API, which would
permit adding the attribute and overwriting files, which nccopy
doesn't permit.

--Russ

> address@hidden> wrote:
> >
> > Meg,
> >
> > > Thanks for your responses to my email.
> > >
> > > When I ran the ncdump -k on one of our netCDF4 files, the response was
> > just
> > > "netCDF-4." Does this mean it's the enhanced model, and it would say
> > > "classic" otherwise? Or is it the other way around?
> >
> > It's the other way around.  The outputs from ncdump -k are one of these
> > four strings:
> >
> >   classic
> >   64-bit offset
> >   netCDF-4
> >   netCDF-4 classic model
> >
> > The "-x" option works to specify NcML output for all but the third of
> > those format variants, "netCDF-4".
> >
> > > I will pass on the information about the java netCDF library to the NOAA
> > > people who run our CLASS archive. They were the ones who were originally
> > > asking about this, and they need to develop code to extract the NcML from
> > > netCDF4 files. So this may be very useful for them.
> >
> > --Russ
> >
> > > address@hidden> wrote:
> > > >
> > > >
> > > > Margaret Tilton - NOAA Affiliate,
> > > >
> > > > Your Ticket has been received, and a Unidata staff member will review
> > it
> > > > and reply accordingly. Listed below are details of this new Ticket.
> > Please
> > > > make sure the Ticket ID remains in the Subject: line on all
> > correspondence
> > > > related to this Ticket.
> > > >
> > > >     Ticket ID: NRE-269426
> > > >     Subject: ncdump -x with netCDF4 files
> > > >     Department: Support netCDF
> > > >     Priority: Normal
> > > >     Status: Open
> > > >
> > > >
> > > >
> > > > The NetCDF libraries are developed at the Unidata Program Center,
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> > Foundation.
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> > > >
> > > > Windows users should see the FAQ list:
> > > >
> > > >
> > http://www.unidata.ucar.edu/software/netcdf/docs/faq.html#windows_netcdf4_2
> > > >
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> > > > If you resolve your issue through one of these methods, please send a
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> > > >
> > > > Best regards,
> > > >
> > > > Unidata User Support
> > > >
> > > >
> > >
> > > --
> > > Margaret Tilton
> > > Cooperative Institute for Research in Environmental Sciences (CIRES) at
> > > University of Colorado at Boulder and
> > > NOAA National Geophysical Data Center, Solar and Terrestrial Physics
> > > Division
> > > 325 Broadway, E/GC2
> > > Boulder, Colorado 80305
> > > 303-497-6223
> > >
> > >
> > Russ Rew                                         UCAR Unidata Program
> > address@hidden                      http://www.unidata.ucar.edu
> >
> >
> >
> > Ticket Details
> > ===================
> > Ticket ID: NRE-269426
> > Department: Support netCDF
> > Priority: Normal
> > Status: Closed
> >
> >
> 
> --
> Margaret Tilton
> Cooperative Institute for Research in Environmental Sciences (CIRES) at
> University of Colorado at Boulder and
> NOAA National Geophysical Data Center, Solar and Terrestrial Physics
> Division
> 325 Broadway, E/GC2
> Boulder, Colorado 80305
> 303-497-6223
> 
> 
Russ Rew                                         UCAR Unidata Program
address@hidden                      http://www.unidata.ucar.edu



Ticket Details
===================
Ticket ID: NRE-269426
Department: Support netCDF
Priority: Normal
Status: Closed