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[UDUNITS #CZQ-242287]: ua v. au

Rick,

Interpretation of a unit string token like "ua" occurs in phases with the first 
match stopping the interpretation: 1) unit name; 2 unit name with a prefix; 3) 
unit symbol; 4 unit symbol with a prefix. Unfortunately, "ua" is a unit symbol. 
Here's its entry:

        <unit>
            <comment>Pre-2012 resolution by the IAU</comment>
            <def>1.495979e11 m</def>
            <aliases>
                <name><singular>astronomical_unit_BIPM_2006</singular></name>
                <symbol>ua</symbol> 
            </aliases>
            <definition>unit of measurement equal to 149.6 million kilometers, 
the mean distance from the center of the earth to the center of the sun 
according to the International Bureau of Weights and Measures (BIPM) in 
2006</definition>
        </unit>

I don't know what they were thinking. Maybe "unit astronomique"?

This is one of the reasons why I recommend the use of unit names rather than 
symbols.

> Had a question about what appears to be a curious inconsistency.
> When is a letter interpreted as a prefix as opposed to part of a
> multicharacter base unit?
> 
> on RHEL 6 (udunits 2.1.19)
> 
> Example 1:
> au is interpreted as atto-u, i.e. atto-atomic mass unit
> 
> a is "are" but
> 
> ua is not "micro-are", but instead astronomical unit.
> 
> How are these ambiguities resolved in udunits2?
> 
> --
> Tschüss ...rick...

Regards,
Steve Emmerson

Ticket Details
===================
Ticket ID: CZQ-242287
Department: Support UDUNITS
Priority: High
Status: Closed