Malcolm,
> "Use FITS" is the default you'll get. We believe, however, that the
> FITS approach is too limiting and inflexible. Therefore the document
> needs to address that conflict directly, and cite practical examples of
> transformations which will not be possible in the FITS model. FITS only
> has three transformations in the CTYPE name (the 4-3-3 notation to allow
> for a project and one distortion) going from pixel to world
> co-ordinates. Yes you can have more than one of these sets just like
> AST, but everything has to be in big sticky lumps, not modular.
> Modularity gives us that extensibility and flexibility.
>
> To summarise: there has to be an introductory section on why we need
> such a set of transformations for the VO.
My initial attempt to promote discussion on IVOA transformations fizzled
out because people were only thinking in terms of its use with WCS. This
lead to an assumption that, since FITS-WCS does everything we need, we can
just use that. I've tried to steer clear of a direct confrontation with
FITS in order to get people thinking about other possible uses and
benefits of a more flexible system. I'm trying to time this document sort
of as a follow up to the recent discussion of Units which has been
happening on the IVOA DM list.
David
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