The udunits package, and the COARDS/CF "units" attribute, just deals with physical units, expressed as powers of base units like length, time, etc.
I think we should consider adding another attribute, called something like "quantity" or "quantity_units" that would try to cover things like "kg N". But can these be standardized, or are they just labels?
Roy Lowry wrote:
> I must say that my instincts are to agree with Jonathan on this. I was very uneasy about the suggestions in the previous e-mails on this issue.
>
> Cheers, Roy.
>
>
>>>>Jonathan Gregory <j.m.gregory at reading.ac.uk> 10/10/06 1:14 PM >>>
>
> Dear all
>
> I don't think it's right to use the units to indicate the quantity, which is
> what kg N would do. COARDS uses special dimensionless units to indicate
> vertical levels in a similar way, but early on in CF we decided to distinguish
> the identification of a quantity from the units it is measured in. The
> quantity being discussed is (for instance) a mass of nitrogen. The units of
> mass are the same for nitrogen, chalk and cheese.
>
> PSU (practical salinity units) is an interesting case in Alison's list.
> This is really a dimensionless number (a mass fraction), so we could survive
> without a unit for it, but it seems less clear to say the salinity is 35 1e-3
> than to say it is 35 PSU.
>
>
>>Clearly with CF1.0 we are stuck with udunits.
>>
>>However, it's worth thinking about the future. I wasn't involved when
>>the decision to be udunit compatible was made. Can anyone summarise the
>>benefits that requiring udunit conformance confer on the CF community?
>
>
> The choice of udunits was made by COARDS. We carry on with it for COARDS
> compatibility. Are there any other similarly comprehensive and flexible
> standards for interpreting units strings? I think the main benefit is to
> provide a general syntax, and secondarily some associated software for parsing
> and converting units.
>
> Cheers
>
> Jonathan
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>
Received on Tue Oct 10 2006 - 14:27:25 BST
