# Coverage.Bounds.Extent, Coverage.Support.Extent

Mireille Louys louys at newb6.u-strasbg.fr
Fri Feb 1 08:40:28 PST 2008

```Jaiwon Kim wrote:
> Dear Doug,
> In the case of a spectrum extracted from a circular region (for example
> a circle with the center x, y and its radius r), what should be values
> for the following metadata defined in SSA/SED?
> Char.SpatialAxis.Coverage.Bounds.Extent
> -- should it be the diameter of the circle? (single value) or two
> separate sizes of a bounding box?
> Char.SpatialAxis.Coverage.Support.Extent Char.SpatialAxis.Coverage.Support.Extent
> -- should it be the area of the circle or something else?
>
>
> Thanks,
> Jaiwon
>
>
Dear Jaiwon,

I think you are right : Bounds describes a bounding box, so
*Char.SpatialAxis.Coverage.Bounds.Extent* could be the diameter value
of the circle, then the
size of the bounding box encompassing the circle.
*Char.SpatialAxis.Coverage.Support* is the circle by itself  , so if
you need to express the circle shape, better use
*Char.SpatialAxis.Coverage.Support.Area*.

see section  5.2.2 of the document: (spectrumDM)

5.2.2 Region definitions
In the optional Char.SpatialAxis.Coverage.Support.Area we describe the
detailed aperture shape
in absolute coords on the sky. However, we don’t allow a full STC region
description. Our
simplified region model allows for (1) a circle and (2) a polygon in a
string representation:
either
circle x0 y0 r
or
polygon x1 y1 x2 y2 x3 y3 ...
for example
circle 233.70 -13.32 0.00043
polygon 233.70 -13.32 233.71 -13.30 ...
where the positions and radii are required to be in degrees, in the
coordinate system defined by
CoordSys.
.....

I hope this helps.
Cheers , Mireille

--
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Mireille LOUYS          mailto: Mireille.Louys at astro.u-strasbg.fr

L S I I T                       &     CDS,
Ecole Nationale Superieure            Observatoire de Strasbourg
de Physique de Strasbourg,            11, Rue de l'Universite
Boulevard Sébastien Brant, BP 10413   67000 STRASBOURG
67412 ILLKIRCH Cedex       	      Tel: +33 3 90 24 24 34
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