Log units (was Re: SED Data Model: Questions and Comments)

[David Berry]

Igor,

> >    So you are suggesting that the IVOA specifies that no data should have
> > logarithmic units? Anyone else got any views on this?
>
> Does it mean, that stellar magnitudes will not be allowed, or I'm missing
> something? It is impossible, astronomers probably will not agree on this!

Magnitude is a bit different because the unit you would use is "mag", not
log(W/m**2/Hz) (or equivalent). That is, you would not expect a simple
unit conversion utility to be able to convert "mag" to "W/m**s/Hz". This
would need extra metadata defining the zero point etc. So I presume Ed
would accept "mag" as OK.

My question related to units in which "log(" appears explicitly in the
units string, such as "log(Hz)"  (strictly the argument of the log
function should be dimensionless, it should be thought of as the ration
between a Hertz value and a fixed zero point of 1.0 Hz). I would expect a
simple units conversion utility to be able to convert from Hz to/from
log(Hz) without any extra metadata etc.

David