[ImageDM] Mapping

[Arnold Rots]

STC does support other axes.
And I am not convinced its mapping is too limited.

  - Arnold

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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 Mon, Nov 25, 2013 at 6:02 PM, Douglas Tody <dtody at nrao.edu> wrote:

> Hi Mark -
>
> I got the impression earlier that you were suggesting doing this by
> adding additional axes to Characterization; sure sounded like it.  In
> any case, for ImageDM/Spectral CoordSys is a place we can put transforms
> that don't fit into either Char or STC - FluxFrame/Photometry is an
> existing example.  In principle Mapping could be be moved there, however
> the complexity and size issue alone is sufficient to argue against this
> (also encapsulation etc. as I noted earlier).  You yourself argued a
> while back that Mapping was Data element specific and should be modeled
> as part of the Data element.
>
> In the case of STC, we did a comparison of STC to FITS WCS a while back.
> STC does have some capability for this, but it is quite limited compared
> to FITS WCS.  Hopefully we don't have to wade through all that again
> (hah!).  Compatibility with FITS WCS and easy transformation to and from
> our VO representations is mandatory if we wish to have any up-take by
> the non-VO community since the community is heavily invested in WCS,
> both in archive data and in client software.  STC could possibly be
> supported as an optional representation, e.g., to specify an output
> projection, and might work for simple projections so long as someone can
> work out the transformation to/from WCS.
>
>         - Doug
>
>
>
> On Mon, 25 Nov 2013, CresitelloDittmar, Mark wrote:
>
>  Doug,
>>
>> The Image and Spectral models have CoordSys outside of Characterisation,
>> and that object is described as basing from the STC astroCoordSys (?)
>> element.
>> So, I am not suggesting we replicate anything.. the STC recommendation
>> already supports the definition of relations (transforms) between
>> coordinate frames.
>> I am suggesting that we use that.
>>
>> I'll do my best to get a diagram of what I have in mind out to the group
>> today.. the Observation/Dataset separation took up my time this weekend.
>>
>> 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.
>>>
>>
>>
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