VOunits draft

[Anita M. S. Richards]

> Perhaps VOunits needs three sections?  1) a list of "thou shalts", 2) a list 
> of "never under any circumstances" - or simply a statement that "units not 
> mentioned (eg, from firkins to fortnights) will not be referenced in IVOA 
> documentation and will not be used in IVOA systems or applications", and 3) a 
> (hopefully brief) list of units that are deprecated within IVOA, but that may 
> be encountered in external data sets and that IVOA applications and external 
> interfaces *may* choose to support conversions to/from.
>
> Rob
>
>

Thanks Rob,

I think that the current document was intending to convey 1) and 3), but 
you put it more clearly.  Right now, since we are consulting on what 1) 
should be, it is hard to be definative about 3) (although if 1) ends up as 
not SI, I will eat my sliderule!).  However, 1) is only a 'thou shalt' in 
terms of how the VO handles the data, we are not even deprecating cgs, for 
example (in the Units model - the VOTable application of it may be more 
stringent), merely saying that it will be converted to SI when being 
handled in the VO.

In fact, if the observatory on Sirius C published data in firkins, and the 
eps Eri team wanted it in fortnightly consumption units or cubic furlongs, 
as long as they provided translation layers, they could write papers in 
the style of Falstaff to their hearts content.  But, I guess that is 
saying 2) with the addition that it does not preclude custom software in 
any units you want.

This is all for conversions which can be invariant and lossless in both 
directions without needing conditional reference points... (which indeed 
covers SI to cgs as long as you remember the cat in electrostatic units)
but  _not_ e.g. yourFilterSystem magnitudes to Jy... although we would 
hope to provide support for tools which do that sort of thing.

best wishes

Anita