Characterisation Working Draft submitted as IVOA document

[Francois Bonnarel]

Dear all,
    If you want to have a look to the Characterization schema
already adressed in the characterisation Working draft
 it will be  possible on Monday in the XML schema section of IVOA documents.

    We revisited our schema since Moscow, complementing the
 documentation inside the schema document and taking carefull
 look once again to STC  features reuse. The Examples document
 has been validated using xmlspy 2005 release and STC August 2006 version.

    We also revisited Arnold's mail of last September, where he
 proposed to reuse high level  STC structures like ObsDataLocation
 and  ObservationLocation to implement the Characterisation schema.
 We think the necessary linkage between fondamental Stc bricks, as I
 already answered late September ,is actually present in our characterisation 
schema.
    But anyway, to complement this discussion , we tried to build an example 
where we should be
 able to reuse something at the level of stc ObsDataLocation, which may
be usefull for collaborative work between Char based applications and pure Stc
based ones .
 This example can be seen at the following URL
 http://alinda.u-strasbg.fr/Model/Characterisation/examples/Char-STC.xml

Discussion:
----------
    ObsDataLocation  is the gathering of one ObservatoryLocation ,one
 ObservationLocation and one PixelLocation

    1 ) We actually do not need the PixelLocation in Characterization =20
 , because
 we consider the data as much calibrated as possible. In any case when the
 data are calibrated we do not describe the mapping. This description=20
 should be part of "Provenance", in the future I think , or a more complex
characterisation model....

   2 ) ObservatoryLocation will be generally borrowed from an STC library

   3 )  So the only  part to consider in more detail is "ObservationLocatio=
n"
    ObservationLocation gathers (several) AstroCoordSys, (several) AstroCoo=
rds
 and (several) AstroCoordArea. Lack of any of them is also allowed.

    Characterization distinguishes Bounds and Support, and
 this distinction is really fundamental for the semantics of the model.

    So what we would actually need is to define a restriction of
 ObservationLocation with a sequence of two AstroCoordArea (one for=20
 the Bounds,
 and the other one for the Support),

    Now we should need also to describe  sensitivity at the same level (her=
e
 and not  in AstroCoordArea, as Arnold suggested, because AstroCoordArea
 is always defining "contours" on the sky, but cannot describe maps
 -that is values everywhere inside the contour- which sensitivity
 is supposed to be doing.)

    So derivating a new type from ObservationLocation by restriction +=20
 extension
 to add this sensitivity we obtain a new type which we can  call=20
 ObservationCoverage,
 because I think it's Arnold's view on what a coverage is.

     4 ) Using this modified version, I tried to figure out what a=20
 Characterization
 axis first xml document will look like, and I obtained the=20
 example shown on the alinda site,  where:
 -  An ObsdataLocation structure including an ObservatoryLocation
 and an ObservationCoverage defined as explained above comes first.
 -  This is followed by the specific characterisation structure with=20
 all actual
 stc structures in coverage  replaced by xml references.

     5 ) This is of course only a partial work, just to show what it=20
 would look like
     a ) in the example I have no Support and Sensitivity at=20
 the moment
     b ) no  ObsDataLocation solution is proposed for Resolution, Accuracy
 and Sampling which remains exatly implemented like in the original=20
 characterisation!!!


    I think it could be an alternative implementation if people prefer, but
 in order to reuse ObsDataLocation features in the characterization=20
 context I would prefer
 to develop a software conversion routine, which I could describe if=20
 people are eager to  examine that


François Bonnarel

PS: Thanks to Mireille for commenting


=====================================================================
Francois   Bonnarel               Observatoire Astronomique de Strasbourg
CDS (Centre de donnees          11, rue de l'Universite
astronomiques de Strasbourg)    F--67000 Strasbourg (France)

Tel: +33-(0)3 90 24 24 11       WWW: http://cdsweb.u-strasbg.fr/people/fb.html
Fax: +33-(0)3 90 24 24 25       E-mail: bonnarel at astro.u-strasbg.fr
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