[ImageDM] Mapping

[David Berry]

On 10 December 2013 17:34, Douglas Tody <dtody at nrao.edu> wrote:
> Hi Mark -
>
> The document at the link below does not load, at least for me.  I also
> went into Volute and poked around, but could not bring it up, so I was
> not able to review the comparision of capabilties.
>
> This looks like the most in-depth analysis yet of WCS vs STC, which is
> good.  It will be good to have such a comparison to inform thoughts
> about future applications or directions, in particular what capabilities
> are missing or added by each WCS formalism.  In the meantime it would be
> good to know the following:
>
>     o   What libraries are currently available that implement STC-WCS,
>         and in what languages?  (I know that there is something at least
>         STC-related in Starlink AST, for example, but do not know how
>         complete it is).

AST support for STC-X (as opposed to STC-S) is rather out of date -
based on V1.20 described at
http://www.ivoa.net/Documents/WD/STC/STC-20050225.html (this is
because there was basically no take-up of the AST support for STC-X).
It doesn't include any support for inter-frame mappings. It just
creates an AST Region from a given STC instance, which you can use for
testing point inclusion, overlap etc.



> Do these libraries support capabilities such
>         as forward and inverse transforms for supported WCS functions?

AST doesn't.

David


>     o   Has the mapping (no pun intended) from FITS WCS to STC WCS and
>         vice versa been worked out and implemented in any libraries?  So
>         for example if we have data with a FITS WCS, can this be easily
>         converted to STC?  How complete is the mapping?  Such easy to
>         use load/save WCS tools would be necessary to enable use the STC
>         formalism with data or applications currently implementing FITS
>         WCS.
>
>     o   Do we know of any current science applications or tools that
>         implement STC for its WCS capabilities?  To what extent is this
>         supported in CIAO or DS9 for example, or other software?
>
>     o   What is the extent of STC WCS support in current archive data
>         collections?  We know that FITS WCS is very widely implemented
>         in current archives (hence supporting it is mandatory), but if
>         STC is becoming more broadly used to describe WCS in archive
>         data, this would increase the priority for supporting it.
>
> Regardless of the technical merits of these two technologies, we need to
> know the answers to the above questions before deciding to favor, or
> possibly even support, STC-WCS for image access and analysis, at least
> in the short term for cube project development over the next 6-12
> months.
>
>         - Doug
>
>
>
>
>
> On Mon, 9 Dec 2013, CresitelloDittmar, Mark wrote:
>
>> All,
>>
>> I've been wanting to get this out for discussion before we get too close
>> to
>> the holidays.
>>
>> In the hopes of settling the debate about whether or not STC provides the
>> capabilities encapsulated in the Mapping object, I have gone through the
>> trouble of making a step-by-step transition of Mapping elements to an STC
>> based model.
>>
>> You can find the document in Volute.  I have also posted the link on the
>> twiki.
>>
>>
>> https://volute.googlecode.com/svn/trunk/projects/dm/ImageDM/doc/Mapping-STC.pdf
>>
>> I'm not sure if this will help or hinder my point in the end, Mapping
>> takes
>> a LOT of information about Frames, Axis linkages, Transforms, etc.. and
>> flattens it to an encapsulation of the FITS WCS serialization (for the
>> most
>> part).  Pulling that out gets somewhat complicated, but in my opinion,
>> anything not in the diagram would need to be explained in the text.
>>
>> ImageDM (and other earlier models) simplified STC elements (Frames),
>> cutting off the complicated inter-system relations that are in the STC
>> objects.  I hope this shows pretty definitively that by NOT simplifying
>> them we get the desired capability, but properly modeled and more
>> flexible.  I think this scenario provides some important benefits:
>>  - uses established IVOA recommendation, so ImageDM can spend its space
>> with use-case diagrams rather than re-defining objects
>>  - enables the 'intermediate' axis set to be realized as actual axes.
>>  - enables scaling of 'Observable' data values
>>  - reduces redundant info.  The Mapping object provides partial WCS Frame
>> information, presumably the full definitions would have to be stored
>> somewhere else.
>>  - reduces irrelevant attributes.
>>  - provides a consistent framework from which we can generalize for
>> general hypercube data and specialize/reuse in the Spectral model to
>> enable
>> 'virtual' columns (which are currently not possible).
>>
>> Please have a look.. hopefully we can have some good discussion over the
>> next couple weeks.
>> Francois and I had some discussion about this approach back in July.. I'll
>> need to dig up those comments and see how they relate to this effort.
>>
>> Mark
>>
>