[CF-metadata] Units micro prefix "u" deprecated in udunits-2

From: Eizi TOYODA <toyoda>
Date: Sat, 27 Mar 2010 09:49:11 +0900

Hi all,

Nobody here is trying to discourage the use of micro sign. What
character encoding are you going to use?

Micro sign (http://www.fileformat.info/info/unicode/char/00b5/index.htm)
is single byte 0xB5 in Latin-1 (aka ISO-8859-1) but becomes
double-byte 0xC2 0xB5 in UTF-8. There is also confusing Greek small
letter mu (http://www.fileformat.info/info/unicode/char/03bc/index.htm)
which is 0xCE 0xBC. In short this letter is bad for computer
processing if we don't have mechanism to specify character encoding.

UDUNITS 2 API has "encoding" argument, and users can choose either
ASCII, Latin-1, or UTF-8. Accordingly "udunits2" command has options
-A -L and -U. It is enough for library that users have control and
responsibility. But CF is a standard of metadata that is exchanged
among people to avoid confusion.

The CF community can choose many ways. I'd like to see views on the community:

(1) Create a global attribute to specify character encoding (like XML)
      I believe this won't work.
(2) Declare that CF uses UTF-8
      Probably many people simply ignore that and put single 0xB5 as micro sign.
(3) Recommends only US-ASCII letters in "units" attribute
      Very conservative, but that is consistent with allowing only
English in standardized attributes.
(4) Do nothing
      I have to warn programmers to anticipate any byte pattern above.
      That would work if only micro sign is an extension to ASCII.

Best Regards,

-- 
Eiji (aka Eizi) TOYODA
Japan Meteorological Agency / WMO/CBS/IPET-MDI
On Sat, Mar 27, 2010 at 00:52, Andrew Clegg <ancl at pml.ac.uk> wrote:
> Hi Julien,
>
> I'm glad you brought this up. We had a discussion about this recently (look
> for any threads with 'udunits 1 or 2 for CF' in the title):
> ? http://mailman.cgd.ucar.edu/pipermail/cf-metadata/2010/thread.html
>
> The best solution (in my opinion) was to use expanded names rather than
> shortened, so instead of using 'u' (which has been replaced by '?' in
> udunits2) you would use 'micro' (which is compatible with both). However it
> would be nice to get a consensus on this or another solution, and some text
> added to the conventions.
>
> Cheers,
> Andrew Clegg
>
>
> Julien Demaria wrote:
>>
>> Hi,
>>
>> I found the "u" micro prefix abbreviation in the current CF-1.4
>> documentation on units:
>>
>> http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.4/cf-conventions.html#units
>>
>> but it seems this prefix is not available in the last udunits-2 (udunits-1
>> is now deprecated)
>>
>> and in udunits-2 they break backward compatibility because the "u" symbol
>> is now used for a new unit "unified_atomic_mass_unit", see in
>>
>> http://www.unidata.ucar.edu/software/udunits/udunits-2/udunits2-accepted.xml
>>
>> http://www.unidata.ucar.edu/software/udunits/udunits-2/udunits2-prefixes.xml
>>
>> So what is the position of the CF community concerning this point, is the
>> "u" micro prefix CF-1.4 compliant or not?
>>
>>
>> Thanks in advance,
>>
>> Julien
>>
>> _______________________________________________
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>> CF-metadata at cgd.ucar.edu
>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>
>
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Received on Fri Mar 26 2010 - 18:49:11 GMT