[ImageDM] Mapping

[David Berry]

To state the obvious, it should be possible to convert from FITS-WCS
to a richer WCS formalism, but may not always be possible to convert
from the richer WCS  back to FITS-WCS. That's the case with AST, which
uses a radically different formalism to FITS-WCS, based on stackable
mappings and a complete separation between mappings and frames.

Modernising AST's support for STC-X may be an option for implementation.

David

On 10 December 2013 23:42, Douglas Tody <dtody at nrao.edu> wrote:
> Hi Mark -
>
> The issue is that all the WCS-related computation we need to do for
> image analysis is currently dealing with FITS WCS instances, e.g., in
> archive data, and the class libraries used in most current applications
> implement the FITS WCS data model as well (WCS instances in archive data
> may or may not involve actual FITS files).  Most of these applications
> are based upon one of the same small collection of WCS libraries, all of
> which implement the FITS WCS model - possibly some other WCS models as
> well, but FITS WCS is what is common.  So far I am not aware of any
> current WCS libraries that support a STC WCS representation.  We have
> some flexibility in how we represent a WCS instance within the ImageDM,
> but we are almost always dealing with a FITS WCS instance or class
> library outside of our VO middleware.
>
> So long as we have a simple mapping to/from a FITS WCS instance and our
> internal VO representation it can work.  Mapping obviously provides this
> since it is merely representing the FITS WCS data model directly using
> VO data model technology, independent of the external serialization.
> Whether or not a simple mapping to/from FITS WCS and the STC data model
> is possible is less clear, especially if we are flexibile in terms of
> representation, e.g., using VOTable and Utypes for the VO serialization.
> We are making progress answering that question - your analysis looks
> like it comes closer to answering the question than anything we have
> done thus far.  It may or may not be possible, however using the VO data
> model technology to leverage widely implemented FITS semantics such as
> WCS is quite an interesting thing to explore as well.  It is essential
> that current WCS-based image processing and analysis applications be
> usable with VO interfaces with modest effort.
>
> In any case, specifying an automated mapping from FITS WCS to/from STC
> would be a good place to start.  It would also be good to have some
> tools (software) to demonstrate such a mapping with real data.  If we
> had that then what you suggest would be a lot more practical to
> consider.
>
>         - Doug
>
>
>
> On Tue, 10 Dec 2013, CresitelloDittmar, Mark wrote:
>
>> Doug,
>>
>> What I believe the document shows is that
>>  - the FITS WCS Serialization ( as encapsulated by the Mapping object ) is
>> compatible with the STC Model.
>>
>> Given that FITS-WCS serialization is a widely used standard, it is
>> important to illustrate that the STC model is compatible with it.
>> I would expect that to have happened before it became a recommendation.
>> It
>> may be useful to have a reference document showing the various FITS-WCS
>> serialization options and their representations in STC objects.  A lot of
>> that information is in the document I just put out, but is not directly
>> shown.
>>
>> But I don't understand the concern behind the questions below.
>>
>> It reads like you are asking how many tools/libraries understand the
>> STC-S/STC-X serializations before considering use of the Model within
>> ImageDM.
>> I don't see the relevance.  All we should need to show is that it is
>> compatible with whatever existing standard serializations are required
>> (FITS-WCS is all I've heard).
>> Is there another Ascii/XML representation of WCS that existing tools do
>> understand?
>>
>> If the concern is that STC may allow additional options not representable
>> by FITS-WCS, I don't think that is a constraint.
>>
>> I feel like we've been around this barn before, so maybe someone else can
>> help illustrate the issue from another angle to help clarify things for
>> me?
>>
>> Mark
>>
>>
>>
>> On Tue, Dec 10, 2013 at 12:34 PM, 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).  Do these libraries support capabilities such
>>>         as forward and inverse transforms for supported WCS functions?
>>>
>>>     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
>>>
>>
>