Hi All,
Reinforcing Martin's point, if a plotting package produces plots labeled with 1e-9 as a unit, I will manually edit the plot to replace the unit with mol/mol, kg/kg, Kg(CH4)/kg(air), or whatever is appropriate. Otherwise it produces great confusion, since the numerical values are different, but not different enough to be obvious. I have seen too many presentations where the units are not clear, or get mixed up within a single talk.
Obviously it would be desirable for the end user if the plotting package put the appropriate unit on automatically. This could be done fairly easily by having a dictionary within the plotting package linked to the std_name, as Martin suggests (or by using grammar rules if/when that becomes standardized), but it would be putting the burden on the plotting package developers to maintain the dictionary.
Best wishes,
Philip
-----------------------------------------------------------------------
Dr Philip Cameron-Smith, pjc at llnl.gov, Lawrence Livermore National Lab.
-----------------------------------------------------------------------
> -----Original Message-----
> From: cf-metadata-bounces at cgd.ucar.edu [mailto:cf-metadata-
> bounces at cgd.ucar.edu] On Behalf Of Schultz, Martin
> Sent: Thursday, April 14, 2011 12:24 PM
> To: cf-metadata at cgd.ucar.edu
> Subject: Re: [CF-metadata] physical vs dimensional units
>
>
> > Message: 6
> > Date: Wed, 13 Apr 2011 14:52:26 -0600
> > From: Steve Emmerson <steve at unidata.ucar.edu>
> > Subject: Re: [CF-metadata] physical vs dimensional units
> > To: cf-metadata at cgd.ucar.edu
> > Message-ID: <4DA60D0A.1010505 at unidata.ucar.edu>
> > Content-Type: text/plain; charset=ISO-8859-1
> >
> > On 04/13/2011 02:25 PM, John Caron wrote:
> > > the point im trying to make is that it would be better to
> understand
> > > that "mol mol-1" (canonical udunit = 1) is not the same as "m3 m-
> 3"
> > > (canonical udunit = 1).
> >
> > In my opinion, the distinction between "mol/mol" and "m3/m3" is
> better
> > indicated by the name of the physical quantity being displayed rather
> > than by its unit attribute. In the cases under consideration, the
> > respective physical quantities would be "amount of substance
> fraction"
> > and "volume fraction".
> >
> > See Table 12 of
> > <http://physics.nist.gov/Pubs/SP811/sec08.html> for more
> > information.
> >
> > For example, the Y-axis of a plot could be labeled "Amount of
> > Substance
> > Fraction of Carbon / 1e-9" to plot nanomoles of carbon per
> > mole of whatever.
>
> Sorry, Steve - but if I would suggest this to any of my colleagues,
> they would declare me as insane. And according to the principle that
> "short and concise is beautiful", I would also much rather continue to
> see plots labeled as "C2H4 [nmolC/mol]" instead of "Amount of C2H4
> fraction of carbon / 1e-9".
>
> I can see the point that this may not be solved by tweaking the units
> attribute. But it means that software that wants to automate the use of
> CF data and present them to users will have to have more "intelligence"
> (well, actually a rather simple dictionary) built in. It's one of those
> areas where good principles collide with pragmatism. Here I see a
> majority of the CF community tending to principles - there were other
> cases in this discussion list where pragmatism reigned.
>
> Cheers,
>
> Martin
>
>
>
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Received on Thu Apr 14 2011 - 13:41:17 BST
