[ImageDM] Mapping

[Arnold Rots]

It all would have been easy to do in STC...

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Arnold H. Rots                                          Chandra X-ray
Science Center
Smithsonian Astrophysical Observatory                   tel:  +1 617 496
7701
60 Garden Street, MS 67                                      fax:  +1 617
495 7356
Cambridge, MA 02138
arots at cfa.harvard.edu
USA
http://hea-www.harvard.edu/~arots/
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On Sun, Nov 24, 2013 at 6:07 PM, Douglas Tody <dtody at nrao.edu> wrote:

> On Sun, 24 Nov 2013, CresitelloDittmar, Mark wrote:
>
>  ... I reiterate that the Mapping
>>
>> information, which defines coordinate systems, should be contained within
>> the CoordSys umbrella, using existing VO standards as much as possible.
>>
>
> The existing WCS formalism (as captured in Mapping) does a lot more than
> just define the coordinate systems used in the Mapping.  The current WCS
> model is comparable in size to Characterization.  Are we suggesting
> trying to replicate all of this within the Characterization model (e.g.,
> the CD matrix, tabular coordinate value / index arrays, etc.).  Note
> also, that in defining a WCS we (or a Photometric calibration and the
> like) are no longer merely defining the characteristics of the dataset.
>
>
>  If the access protocols have a need for an object which encapsulates all
>> of
>> the Mapping information under one object, then I suppose that could also
>> be
>> provided.  It would not be part of the data product, but would hold
>> information extracted from a data product.
>>
>
> It is not merely a matter of providing the Data element metadata in an
> object (although that is important), but a matter of complexity,
> information hiding, and re-use.  Data models become increasingly baroque
> and awkward the larger they become.  We are better served by having data
> models with a well-defined scope and purpose, and associating multiple
> such data models to model complex use cases.  Re-use is important not
> just for the VO data models but for existing data models in wide use
> within the astronomical community, FITS WCS being a prime example.
>
> Re adding additional axes to Characterization - yes that can be useful.
> Adding an axis to characterize visibility data could be a good example.
>
>         - Doug
>
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