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[netCDF #XYX-140598]: Question about "_Unsigned" variable attribute

Hello Meg,

I do not know offhand what the status of this in terms of the CF Conventions; a 
quick search revealed this comment thread started by John Caron in October 2014:

* https://github.com/cf-convention/CF-2/issues/3

There is also a comment thread regarding unsigned bytes here:

* https://github.com/Unidata/netcdf4-python/issues/493

This does not appear to be adopted in the latest CF conventions (1.6), which 
instead says:

    All integer types are treated by the netCDF interface as signed. It is 
possible to treat the byte type as unsigned by using the NUG convention of 
indicating the unsigned range using the valid_min , valid_max , or valid_range 
attributes.

The bottom line, however, is that I am not a CF convention expert and any 
guidance I can provide is probably too shallow for you to base this decision 
on.  Your best bet will be to ask on the CF-metadata mailing list; information 
about that list can be found here:

* http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata

Regarding support by the standard libraries; I would expect these standards to 
be supported at the library level.  With the exception of the Java libraries, 
the python, fortran, etc libraries are merely interfaces to the C library, and 
not re-implementations.  The `_Unsigned` attribute is no different than any 
other attribute, from a technical standpoint; the more likely source of failure 
would be whether or not upstream software respected the `_Unsigned` attribute 
and/or used it as it was intended.

I'm very sorry I can't give you a better answer re: the state of the current CF 
conventions.  Hopefully, one of the members/scientists on the mailing list will 
be more informed.  In the meantime, will forward this email along to a couple 
of people who may know, but it will probably be a little bit before I hear back 
and there's no guarantee they'll have any better answer.

Have a great day, I hope this information is at least somewhat helpful,

-Ward

> Hi,
> 
> Your netCDF "Best Practices" website
> <http://www.unidata.ucar.edu/software/netcdf/docs/BestPractices.html> says
> that the use of "_Unsigned = true" is a new proposed standard for alerting
> users that data needs to be converted to unsigned format.
> 
> Do you know what the status is on this standard? We ask because a
> high-profile data set has been designed to use this attribute extensively.
> We are concerned users will find it confusing and standard libraries --
> e.g., the netCDF4 Python library -- won't be able to read it.
> 
> The data set in question will be used for many years, however. So if the
> standard has moved beyond the "proposed" phase and is being implemented,
> this may be less of a problem than we anticipate.
> 
> We are trying to figure out if the data format should be changed to avoid
> this attribute. Such a change may involve significant work.
> 
> Thanks in advance for any guidance.
> 
> Meg Tilton
> 
> 
> --
> Margaret Tilton
> Cooperative Institute for Research in Environmental Sciences (CIRES)
> at the University
> of Colorado and NOAA National Centers for Environmental Information (NCEI)
> 325 Broadway, E/GC2
> Boulder, Colorado 80305
> 303-497-6223
> 
> 


Ticket Details
===================
Ticket ID: XYX-140598
Department: Support netCDF
Priority: Normal
Status: Closed
===================
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