I would recommend to use degrees everywhere in our constructors and region
strings. We can have a constructor for sexagesimal points. These always
appear as pairs of ra-dec.
--Alex
-----Original Message-----
From: owner-voql-teg-at-eso.org [mailto:owner-voql-teg-at-eso.org] On Behalf Of
Patrick Dowler
Sent: Wednesday, May 14, 2008 4:22 PM
To: voql-teg-at-ivoa.net
Subject: degrees vs radians, legal ranges
I looked through the trig functions in SQL (all radians as far as I can
tell)
and since there are DEGREES and RADIANS functions for converting, I think it
is a given that SIN, COS, etc use radians.
But then we have to decide if the geometry "constructors" take radians or
degrees. Radians are really not user-friendly and I am pretty uncertain
about
which would be better. It has to be explicit, for sure, and it is a matter
for the ADQL definition rather than a TAP (or other) service metadata to
specify it. The point of ADQL/s is that expert users could use it the same
way they use SQL: type in a query and execute it!
Also, astronomical name resolvers return sexigessimal or degrees and never radians, so we seem to be on the boundary here...
--
As for Mark Taylor's comment about legal ranges, it seems that DB trig functions do range-reduction in some cases and fail in others (in my tests).
However, with long/lat it is only safe to do it for longitude (because it wraps around independent of latitude).
So, we should specify the legal ranges, where I think [0,360] and [-90,90]
are
the sensible choices. For simplicity, we should say that using values
outside
these ranges is an error.
If a specific service is non-compliant with that by performing
range-reduction
I don't think it will break anything. That puts us in the same state as with
the built in trig functions (which may behave inconsistently and I don't expect service providers to catch and map those inconsistencies).
--
Patrick Dowler
Tel/Tél: (250) 363-6914 | fax/télécopieur: (250) 363-0045
Canadian Astronomy Data Centre | Centre canadien de donnees astronomiques
National Research Council Canada | Conseil national de recherches Canada
Government of Canada | Gouvernement du Canada 5071 West Saanich Road | 5071, chemin West Saanich Victoria, BC | Victoria (C.-B.)Received on 2008-05-16Z00:00:12