Why not pack data into unsigned int types?

[gfireman]

Conventions say:

...the variable containing the packed data must be of type byte , short or int .

Why not ubyte, ushort, or uint?

We typically pack data into unsigned int types.
To be CF compliant we'd have to change types - and then adjust scale_factor and add_offset to recover the range lost to a sign bit.

[cofinoa]

When the CF convention was written, the netCDF format only supported signed types. This restriction on data model support, it's named netCDF classic model in the current netCDF data model:
https://docs.unidata.ucar.edu/netcdf-c/current/netcdf_data_model.html#classic_model

Probably, support for new types could be proposed as an enhancement.

P.S.: This out of scope for the CF Convention, but if you are using writing packed data to encode new data, you can apply netCDF4 chunking feature, apply shaving to non-significant bits on the float number, and add the deflate filter, honouring classic data model and CF, without the use of CF packed data feature and using float/double original type.

[gfireman]

The CF convention does allow for unsigned integer types, just not for packing float/double into.
Interesting suggestion on using compression instead of scaling. We'll run some tests and see how that works for us.
Thanks!

[cofinoa]

yes, you are right!! The restriction on classic data model was removed on CF-1.9, allowing, among others, some data types from the enhanced data model. The Packed Data sections wasn't updated following that.

[larsbarring]

Can this issue now be closed as answered following the completion of #374 via PR#456?

[JonathanGregory]

Yes, I think this question is now answered.

[JonathanGregory]

Dear Gwyn @gfireman

I'm closing this issue now, because it's been addressed by a recent update to the working version of the convention (that will be released in a month or so). Please see the updated section 8.1. Thanks for asking the question. If it's not completely answered, please feel free to reopen this issue.

Cheers

Jonathan