SIA 2.0 POS parameters

[Patrick Dowler]

RANGE is a pain if you hav to do transformations. In the current WD, it 
is true that is is only usable if you want a coordinate range in ICRS 
and I think that generally implies searching large chunks of the sky 
(maybe methodically) because a range in ICRS doesn't correspond to any 
objects you might be studying. OTOH, a range in GAL would be useful to 
easily search in or away from the galactic plane...

Previous discussions highlighted that CIRCLE is the useful search shape 
when people are studying know astronomical objects (outside solar 
system). POLYGON is the useful search shape if you are trying to find 
data that overlaps some other data you have in hand (for now, lets 
ignore the more subtle issues of amount of overlap, intersects vs 
contains, etc).

That leaves RANGE, which in a restricted coordinate system is only 
really useful for methodical search of a large area, broken down into 
pieces. It could be almost duplicated with polygon (ignoring difference 
between great circle and line of constant latitude) except in the cases 
where you use open-ended ranges (stripe in DEC, range of RA from pole to 
pole)... even those can be done with a couple of polygons instead of one 
range.

So, yes RANGE is a convenience shape with rather limited use and would 
be a pain to implement correctly if your DB is not in ICRS. But it is 
useful and convenient for the large fraction of the data that is in 
ICRS(ish)...

Pat

PS-Separate email on non-ICRS use to follow

On 08/07/14 11:04 AM, Walter Landry wrote:
> I have a dataset with extremely narrow rows.  Storing both coordinates
> would increase storage by 25%.  So I store and index everything in
> ICRS and convert as needed to GALACTIC.  Doing RANGE queries in
> GALACTIC would be prohibitively expensive.  BOX and POLYGON queries
> are fine.
>
> I guess the upshot of this is that I am starting to feel more strongly
> that RANGE should be removed from SIA v2.


-- 

Patrick Dowler
Canadian Astronomy Data Centre
National Research Council Canada
5071 West Saanich Road
Victoria, BC V9E 2E7

250-363-0044 (office) 250-363-0045 (fax)