[fitsbits] REGION extension -- examples?

[Tom Jarrett]

Arnold,
On further thought, the Spitzer group feels that the
REGION definition used by Chandra (namely pixel coords
with WCS) will work satisfactorily with Spitzer spectral products.
So we are going to give this a try.  The two examples that you sent
to me (see note below) are helpful.  However, we have not successfully
been able to make these work with DS9 (version 3.0b6).

Before we start coding, we really need an example that we can work with.
Arnold, can you check your examples with DS9 and get back to me on that?
Can the fitsbits group point me to any other FITS examples
with REGION definition in the header?

Many thanks, -tjarrett

Arnold Rots wrote:

> 1. Attached are two files.  One shows the FOV of a Chandra observation,
> the other a series of elliptical source regions, produced by a source
> detection program (though it is a somewhat convoluted format).
> 
> 2. You can use the COMPONENT column to indicate multiple regions - or
> any additional column of you choice. But note that the Region
> definition is purely positional and 2-D.
> We use HDUCLASS='ASC' and HDUCLAS1='REGION' to identify these
> extensions (though admittedly, the second example has these keywords
> overridden).
> But we definitely put multiple regions in one extension.
> DS9, btw, can read FITS region files - it just doesn't write them.
> 
> 3. We express our coordinates in terms of pixels, but as far as I can
> see there is no reason why they could not be celestial coordinates.
> You might have to stipulate that "lines" are to be interpreted as
> great circles - which is fine for tangent point projections.
> Also note that the next generation region are specifically defined in
> terms of celestial coordinates.  I just posted a new version of the
> VO Space-Time Coordinate Metadata document that contains the region
> description and schema.
> See http://hea-www.harvard.edu/~arots/nvometa/v1.2
> 
> Hope this helps,
> 
>   - Arnold
> 
>