ADQL geometry types

[Walter Landry]

Patrick Dowler <pdowler.cadc at gmail.com> wrote:
> I have just posted an update to WD-DALI-1.1 with what I think is now a
> complete set of xtype values and serialisation rules (essentially
> using VOTable arrays of numbers).

For anyone like me who tried to find the document, it is at

  http://wiki.ivoa.net/internal/IVOA/DALI-1_0-Next/WD-DALI-1.1-20160415.pdf

<snip>
> 2. Deprecate REGION; no replacement. This means that ADQL and TAP will
> no longer support that highly problematic polymorphism within columns
> (e.g. columns that can contain a mix of circles and polygons -- only
> concrete types) and no more string manipulations or conversions.

Given that it is unlikely that I would ever be able to implement this
for most of our datasets, I am happy to see it deprecated.

<snip>
> A related issue w.r.t. WD-DALI-1.1:
> 
> 4a. Deprecate BOX; no replacement.
> 
> 4b. Overload BOX with a version that lacks coordinate system metadata
> *and* define it in DALI.
> 
> 4c. Define a range-valued function (COORDRANGE?) in ADQL.
> 
> BOX and range (concept used in SIA-2.0) differ and DALI does not
> currently define either... no one really spoke up for range in DALI
> discussions and some spoke out against it in SIA-2.0 discussions, but
> it remained in SIA-2.0... I am in favour of leaving range out of DALI.
> I would prefer 4a since the value of BOX exceeds the complexity.

BOX and RANGE are aligned to a coordinate system, which feels out of
place.  So I am happy to not have them.  In addition, BOX is annoying
to implement.

I will add a vote for an ELLIPSE type.  Our users have error ellipses
and depend quite heavily on searching within them.  It can be
approximated with a POLYGON, but that is a lot more work for the
client.  In terms of existing implementations, pgSphere, mysql_sphere,
q3c, and our libtinyhtm all support ellipses.  On the other hand, the
GIS systems for Postgres, Oracle, and MS SqlServer do not have it.  So
it will be extra work for some systems.

Cheers,
Walter Landry