SIA 2.0 POS parameters

[Walter Landry]

Jose Enrique Ruiz <jer at iaa.es> wrote:
> Hi Walter, DAL
> 
> 
> 2014-06-27 22:24 GMT+02:00 Walter Landry <wlandry at caltech.edu>:
>>    This would also make the Range geometry more useful.  There are not
>>    that many things that align themselves along lat/lon lines in ICRS.
>>    Though to be honest, I would be happy enough to get rid of Range.
>>    Polygons and Box (see below) would cover most of the use cases.
>>
> 
> In the case of discovery (SIA 2-0) I understand that the response/output
> image of a discovery query does not need to be aligned with any geometry.
> POS is intended to define the spatial dimension of ROI for *discovery*. In
> the case of AccessData I agree RANGE is not very useful for cutouts, like
> CIRCLE I think it's better suited for discovery purposes.
> 
> This reminds me that it would be good to define in the SIA 2-0 specs ,the
> degree of intersection between ROI and the response image.

I do not understand.  For discovery, it is simple enough to create a
polygon with the four corners.  The main difference is that the
corners will be joined by great circles rather than lines of constant
latitude.  I do not see how that would cause a problem.

>> 3) Why isn't there a Point geometry?  I can specify a circle with
>>    radius zero, but that is awkward and un-intuitive.
>>
> 
> I take this a use case for AccessData specs, though right now I can only
> think on extracting single-pixel spectra from a spectral datacube..

No, this is a use case for SIA.  I want all images that cover a
source.  Similar arguments apply for all of the other cases you cited
as applying only to AccessData.

Cheers,
Walter Landry