[Units] : (Was: Re: SED Data Model: Questions and Comments

[David Berry]

On Wed, 16 Feb 2005, Brian Thomas wrote:

>  I have no problem with this, and would go for this point of view because it provides
>  a many to one translation layer.. e.g.
>
>  units system A ---> DM Units model --> units system B

I guess you were referring to the dimensional analysis model as the
"common" moddel in the middle. This raises another question I had.
Whereas the conversion from string to dimensional analysis is well
defined, is the inverse conversion well defined? That is, given a
dimensional analysis and a scale factor, does it imply a single units
string? If not, I guess many of the possible strings will be equivalent,
but some may not be. Again the issue of dimensionless units such as
steradians, degrees, pixels, etc, could mess things up. If you convert
"Jy/sr" to dimensional analysis form and then convert back to string do
you get "Jy/sr" or "Jy". These are obviously very different.

David