towards 3D data model

[Doug Tody]

Francois -

The characterization data model (also other general dataset data models 
such as identification etc.) apply to all datasets hence would apply to
3D data as well.

For modeling 3D data in DAL, more is required as we need to model the
actual dataset.  Currently we have 2D sky images (SIA) and various kinds of
tabular spectrophotometric data (SSA).  My feeling is that what is required
for spectral datacubes is a generalization of the 2D image model to 3D.
This would build upon the spectrophotometric metadata developed for SSA to
describe the observable, plus FITS WCS to describe the coordinate system.

This is probably what is needed for regularly gridded data such as a
spectral data cube.  It is also possible that for some data of this sort,
e.g., MOS or IFU data where the spectra have already been extracted, that
we should use the SSA data model instead.  It would be easy to extend
this to collections of spectra, which is what one has in this case.

It is possible that to support spectral data cubes we should just
fold the support into a future version of SIA - whether or not this is
advisable depends upon how much it complicates things.  It may be that
the complications would justify a new data access interface for 3D data.
In particular, we don't know at this point what is required to cutout
regions of a large spectral data cube.  We need to understand the science
drivers better to analyze this, i.e., what sorts of analysis do we want
to target with this capability.

	- Doug


On Mon, 14 Feb 2005, Francois Bonnarel wrote:

> dear Giovanni, Phillipe and Igor,
>    I am happy that Euro 3D people will join the IVOA data model effort
> This connection was missing since a long time. I am not personnaly sure
> that creating a specific 3D data model is the best we can do to achieve
> that. There is an ongoing "Characterization" data model effort supposed
> to deal with any kind of observations and data sets.  (material can be found
> on the list about that, and Giovanni, you can remember we discussed this last 
> October). A subgroup is supposed to produce a draft long before Kyoto for 
> discussion.
> My immediate proposal is that somebody among Euro3D people can join the 
> subgroup  and judge the pertinance of the ongoing work from the 3D point
> of view.
>   Your opinion about that ?
> Cheers 
> François
> 
> =====================================================================
> Francois   Bonnarel               Observatoire Astronomique de Strasbourg
> CDS (Centre de donnees          11, rue de l'Universite
> astronomiques de Strasbourg)    F--67000 Strasbourg (France)
> 
> Tel: +33-(0)3 90 24 24 11       WWW: http://cdsweb.u-strasbg.fr/people/fb.html
> Fax: +33-(0)3 90 24 24 25       E-mail: bonnarel at astro.u-strasbg.fr
> ---------------------------------------------------------------------