Capability extension for describing whole sky maps

[Tom McGlynn]

It seems to me that there are three things being combined here:

    All-sky data
    Hierarchical imaging
    HEALPix projection

The first and last don't seem particularly special to me: many surveys have
had all-sky coverage for a long time.  Nor does HEALPix seem particularly different.
It's just another projection, albeit one that a lot of software does not yet
support.  What strikes me as distinctive for the new Aladin service is the
hierarchical imaging, which I don't think is well described in our current framework.

So I think that's the element I'd emphasize rather than HEALPix which I see as a detail
in a particular implementation.  E.g., WWT proides a similar service using the TOAST
projection and I believe GoogleSky does the same using a Cartesian projection (or maybe
even Mercator).

	Regards,
	Tom


Pierre Fernique wrote:
>
> Dear registry members,
>
> As I presented Tuesday 18 May during the App session at Victoria
> interop, I was suggesting an extension of the "capability" section for
> describing whole sky maps/surveys (for those who do not follow this
> talk, here the pdf -
> http://www.ivoa.net/internal/IVOA/InterOpMay2010Applications/AladindemonstrationInteropVictoria2010.pdf).
> Do you think that it is a good idea. And if yes, may you help me for
> describing it properly in the schema of the registry.
>
> Here is my draft :
>
> <capability xsi:type= "SimpleAllSkyAccess">
> <interface type="HEALPIXmap">
> <accessURL use="base">http://..</accessURL>
> <HEALPix>
> <frame>Gal</frame>
> <tileFormat>FITS</tileFormat>
> <treeDepth>12</treeDepth>
> </HEALPix>
> </interface>
> …
> </capability>
>
> type : HEALPIXmap, HTMmap,... = sky tessellation method
> frame : GAL, ECL, EQU = tessellation reference frame
> titleFormat : FITS, PNG, JPG .... = image format for individual tile
> treeDepth: number = hierarchical depth (in Healpix = Norder, or log2(NSIDE))
>
> This kind of "SimpleAllSkyAccess" resource may be queried just by tile
> ID as parameter. For Healpix it is a couple : Norder/npixNumber. For HTM
> it will be the triangle ID...
>
> http://base.adresse..cgi?tile=ID
>
> With this very simple interface, any body should be able to build a
> client for displaying this kind of resources.
>
> Thanks
> Pierre Fernique
>