general comments to SSAP and SDM from outside

[Doug Tody]

Hi Petr -

On Mon, 17 Sep 2007, Petr Skoda wrote:
> > The suggestion to add "normalized" as a form of flux calibration is
> > something we should consider.
> 
> Thanks for support of my idea - Jonathan has put it in the new revision od DM
> - will it be updated in the SSAP as well ?

Yes, it has already been added.

The SSA specification has been updated in response to the RFC (which
closed last week), and a new version is being circulated now among the
authors.  This will be released on the DAL list in a couple of days.
This is about to go to REC and be frozen so V1.0 won't change much
after this, but there will be a V1.1 (with getCapabilities etc.) in
a few months, so development can continue as necessary.

> > > Regarding support for IRAF-Onedspec format for spectra (a linearized
> > > spectrum represented as a 1-D image), I feel this is too limited a
> > > format to be pushed as a new general standard,
> 
> OK - I agree its limited (esp. problems with merged echelle spectra
>  are quite often met) but I do not want to define it as a recommended standard
> but as a tolerated option.

It is already possible for a service to output this as a format;
the only question is how much we want to encourage this (one could
say there are already too many formats).

In any case, SPLAT, VOSpec, Specview, IRAF, the JHU Spectrum Services
client, etc. are all already being updated to support SSA (all of these
already have some SSA capabilities).  For legacy client applications
(FORTRAN etc.) which cannot easily be changed, they won't even be
able to do a SSA query and parse the XML that comes back, so I think
a better approach is to have a separate client application that can
do the query and write out the spectrum in the format required by the
legacy app.  Probably lots of spectra client apps will be able to do
this, if there is a need (e.g., we could easily add this capability
to VOClient).

> But something as the "continuum model" would be surely needed.
> There is a number of techniques of continuum fitting and the proper
> description of them may be quite complicated in simple keywords..
> On the other hand, even now there is rather uncommon to publish original and
> normalized spectra in a consistent way - no 1to1 association of two separate
> files - only few packages store the continuum shape together with original
> data

This is where I think we ultimately need to go with this.  For a
continuum normalized spectrum we should include the normalization
function in with the spectrum, and provide enough metadata to
describe what type of normalization was done.  Then people would be
more likely to publish their data this way.  Something to consider
for the next version.

Sounds like we will have plenty to talk about in Cambridge next week!

	- Doug