CF valid units that are not in UDUNITS

[mhidas]

The CF FAQ page says:

There are two units acceptable to CF that are not in the UDUNITS library: sverdrup, and decibel or dB. These have been requested for inclusion in future versions of the UDUNITS library.

Looks like "sverdrup" is already in UDUNITS-2. "decibel" and "dB" are not. There is an open request to add it (Unidata/UDUNITS-2#33), but the discussion there suggests this may not be possible in a generic way, i.e. without specifying a reference value.

Would it be possible to get cf_units to recognise "dB" and "decibel" (as effectively dimensionless units), independently of UDUNITS?

[ocefpaf]

Thanks for reporting this @mhidas.

cf_units goal is to be CF compliant, so we should try to include those. I will see what we can do and get back to you.

[rhattersley]

FYI, @hasselldc ships a modified UDUNITS database in cf-python.

[ocefpaf]

Thanks @rhattersley! I will take a look and, if possible, push it upstream to UDUNITS-2.

[ocefpaf]

• level
• layer
• sigma_level
• decibel, dB

[ocefpaf]

Note to self: Unidata/UDUNITS-2#42

[mhidas]

Has there been any progress on this issue?

I don't think any of these units will make it into UDUNITS any time soon, if the (lack of) activity in those issue threads (Unidata/UDUNITS-2#33, Unidata/UDUNITS-2#42) is anything to go by.

[pelson]

Has there been any progress on this issue?

It doesn't appear so. Unidata/UDUNITS-2#42 does look promising. Adding custom udunits definitions is also an option. Given the relevance of the CF documentation, if you have a proposal for moving this forwards without adding significant complexity to cf_units then I can't see that it would be a problem to merge.

[mhidas]

Thanks @pelson . I've commented on that UDUNITS PR to see if there's a chance of getting it merged. If there's no response I'll look into proposing a solution here.

[trexfeathers]

@ocefpaf sorry for gravedigging but Unidata/UDUNITS-2#42 was finally merged last year. Any thoughts on this issue?

[ocefpaf]

We can backport it as a patch but I'd rather ask upstream for a new release. The latest one is https://github.com/Unidata/UDUNITS-2/releases/tag/v2.2.27.27 from Nov 20, 2020 and that PR (from 2016!) was merged on Mar 17, 2021.

[stephenworsley]

It looks like the last release was Feb 1st 2022 but this was not tagged Unidata/UDUNITS-2#104. So it looks like this ought to be in a released version.

[larsbarring]

Please note that the CF FAQ text referred to in the opening comment is not up to date.

[trexfeathers]

From @SciTools/peloton, can this be:

A: closed?
B: progressed?
C: re-assigned if @ocefpaf is busy?

[ocefpaf]

I had no idea it was assigned to me :-)
I vote for A and, if folks really need this, someone will re-open the issue and/or send a PR. My guess is that most downstream Software that requires these units end up patching and/or adding them via a custom xml file.