Description of HEALPix in STC

[Arnold Rots]

Thomas,

With apologies, I did not have an opportunity to respond earlier.


HEALPIX is recognized as a coordinate flavor in STC and one can
specify positions (and lists of positions) and regions in HEALPIX
coordinates.

As an aside, Tamas Budavari is the original author of the STC region
library using HTM; that may be relevant to you, too.


If you are happy with using region specifications (for instance,
polygons), then it is easy to do in STC-X, but it wil also work in
STC-S.

The current version of the STC-S document:

    http://hea-www.harvard.edu/~arots/nvometa/STC/STC-S-20090724.pdf

defines the Space Sub-phrase as, for instance:

  Polygon [fillfactor <fill>] <frame> [<refpos>] [<flavor>] [<pos> ...]
   [Position <pos>] [unit <unit>] [Error <error> [<error>]]
   [Resolution <resln> [<resln>]] [Size <size> [<size>]]
   [PixSize <pixsiz> [<pixsiz>]] [<Velocity sub-phrase>]

For your purpose only the first line is of interest and you can fill
it simply as:

  Polygon ICRS TOPOCENTER HEALPIX [<pos> ...]

(Formally, the document does not mention HEALPIX as an option, but
that is because that section did not get updated when HEALPIX was
introduced)

The only issue is, if you want values for Healpix h and k that are
different from the defaults (4 and 3, respectively), we need to find a
way to accommodate them.


Does that help?
Cheers,

  - Arnold


Thomas Boch wrote:
[ Charset ISO-8859-1 unsupported, converting... ]
> Hi,
> 
> I'd like to describe in STC the coverage of a catalogue as a union of a 
> set of HEALpix pixels, possibly mixing different levels of pixelisation. 
> I am in particular seeking for examples of a serialization (STC-X or 
> STC-S) of such a description.
> As I could not find such an example in the STC document, I'm seeking for 
> your help.
> Cheers,
> 
> Thomas
> 
> -- 
> Thomas Boch
>   CDS/Observatoire Astronomique   Phone  : 33 (0)3 68 85 24 42
>   11, rue de l'Universite         Fax    : 33 (0)3 68 85 24 17
>   F-67000 Strasbourg              Email  : thomas.boch at astro.unistra.fr
>   France                          http://cdsweb.u-strasbg.fr/~boch 
> 
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Arnold H. Rots                                Chandra X-ray Science Center
Smithsonian Astrophysical Observatory                tel:  +1 617 496 7701
60 Garden Street, MS 67                              fax:  +1 617 495 7356
Cambridge, MA 02138                             arots at head.cfa.harvard.edu
USA                                     http://hea-www.harvard.edu/~arots/
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