IVOA Footprint Service Protocol

[François Bonnarel]

Dear NVO partners,
Dear DAL  WG chair and members,

       I think that probably all the authors of the VOTABLE/footprint 
note will agree with me
that sharing experience among developpers of footprint applications is 
usefull and could
be made under the responsability of DAL (or application ? or joint ?) 
IVOA WG.
First thing would be to review the use cases each of these applications 
can fulfill and
to try to reach some convergence in next versions, as well as 
developping some converters
when necessary.
      But I definitly DON'T think we are in a situation where it should 
exist ONE single
way of doing this.
   See more detailed and some time "nervous" answers to the points 
adressed by Roy's
mail below....

Regards to all
François Bonnarel

Roy Williams wrote:

> Keith (as DAL chair)
>
> I am writing to discharge a task I have been given by the NVO Team 
> Meeting, which is just finishing this afternoon. We have had a 
> discussion of Footprint formats and Footprint services, and we would 
> like you to start a new activity within DAL to standardize these 
> services across all footprint servers.
>
> Perhaps we could start by asking for proposals from DAL group members 
> about how these protocols might look? Below are some notes and URLs 
> that I hope will set the scope. I am assuming that everyone who wants 
> to participate will be on the DAL mailing list.
>
> Roy
>
> ------------------------------------------
>
> -- How should footprints be described? Presumably by a text 
> serialization in the IVOA standard [1] or non-standard [2],[3] 
> formats. Or through a reference to a footprint, by an IVO or http 
> reference. Or as the footprint that belongs to a survey (eg. "the SDSS 
> footprint"). What other ways are there to get a "handle" on a sky 
> footprint? 

     Sorry , I contest that 1 is "in the IVOA standard" and 3 is not. We 
are definitly using VO standards and Technology for
a footprint interoperable APPLICATION.
            1)  The general VOTABLE container is a standard
             2) SIA ans SSA to which our footprints can be attached are 
standard VO technology
             3) the extension mechanism which is used for this attchment 
is described (shortly indeed but anyway described)
in the SSA recommendation
             4) the utype concept and attribute is described in the 
VOTABLE standard. It is extensivly used and
referred by SSA, SDM and Char standards.
              5) there is a Note by Jonathan suggesting how STC utypes 
could be written and a Note
by F Ochsenbein about integartion of STC Coord systems abd utypes in 
catalog votables.
              6) It is true that none of these have the satus of a 
recommendation, but it is the same for
all the utypes, simply because the utype discussion is not OVER!

>
>
> -- What methods can be applied to a footprint? Intersection, Union I 
> would think. Find the area on the celestial sphere. Does it contain a 
> given point? Which of a set of points does it contain? Methods to 
> serialize footprints, perhaps to make images of them, or to make 
> polygons on Google Sky?
>
> -- What services are already prototyped? I know of the Aladin system 
> [4] and the JHU services [5]. Who else is involved in sky footprint 
> work besides these? 

      [3] is not describing any "Aladin system" but the "ESO/CDS  
footprint facility."
          this effort was started within the scope of VOTECH project as 
early as Spring 2005.
      First prototypes were demonstrated in VOTECH meetings fall 2005 
and March 2006
     IVOA can be aware of that since Spring 2006
        there was a presentation in Application by Thomas Boch and 
another one by myself in
       DAL in Victoria. The whole thing was again presented in the small 
projects meeting   
      in Moscow.
       HST APT adopted the first version of the format early 2006.
       ESO has built  and distruibutes  VirGo and  SIA / SSA services  
using this
since a couple of monthes.
       So it is no more a prototype it is a set of operational services 
using VO standards.

        We never pretended to have built a STANDARD bu to use EXISTING 
standards
      for actual INTEROPERABLE work.

>
>
> [1] IVOA STC: http://www.ivoa.net/Documents/latest/STC-Model.html
> [2] Linear STC (A. Rots): 
> http://www.ivoa.net/Documents/latest/LinearSTC.html
> [3] VOTable STC (Aladin group): 
> http://www.ivoa.net/Documents/latest/Footprint.html
> [4] Aladin: http://aladin.u-strasbg.fr/
> [5] JHU footprint services: http://voservices.net/footprint/
>