DALI v1.2: shape vs ESO and ALMA

[Patrick Dowler]

> C) Does DALI 1.2 allow a user to express spherical coordinates or
geometrical types in non-equatorial frames?

DALI assumes that the coordinate system metadata is specified elsewhere,
e.g. using coords DM and mivot to annotate the column. We are trying to be
less restrictive so that one could use DALI geometry with more than just
ICRS (eg galactic) and more than just spherical (long,lat).


--
Patrick Dowler
Canadian Astronomy Data Centre
Victoria, BC, Canada


On Tue, 5 Dec 2023 at 09:22, alberto micol <amicol.ivoa at googlemail.com>
wrote:

> Hi DALers,
>
> Two strong comments (A and B) and one question (C), regarding DALI v1.2...
>
>
> A) §3.12 Shape states: "The allowed shapes are: circle, range, polygon.”
>
> ESO needs to have also:
> - point
> - multi-polygon
> and, because of ALMA, also:
> - union of circles and polygons, also with holes, where holes are
> expressed as CW polygons.
>
> Otherwise we will not be able to adopt DALI 1.2
>
> But it would be best for the standard, if “shape” could be fully
> polymorphic, that is, if it could support all the DALI geometrical types,
> which are:
> - 3.6 Points
> - 3.7 Circle
> - 3.8 Range
> - 3.9 Polygon
> - 3.10 MOC
> - 3.11 Multi-Polygon
>
>
> B) §3.9 Polygons states that:
> “In spherical coordinates […] Vertices must be ordered such that the
> polygon winding direction is counter-clockwise (when viewed from the origin
> toward the sky) as described in (Rots, 2007). “
>
> That is not the correct definition, as it excludes the possibility to
> express a hole using a CW polygon.
>
> As I expressed at the IVOA in Bologna earlier this year, the only standard
> that completely defines spherical polygons is the STC v1.33, 2007. All
> other standards (ADQL 2.0, TAP 1.0, DALI v1.1, etc) do not do the right
> job. If interested in details, please see:
> https://wiki.ivoa.net/internal/IVOA/InterOpMay2023Ops/ESO_VO_Polygon_Tool.pdf
>
> My suggestion is not to define the polygon in DALI, but simply refer to
> the definition provided by STC v1.33, 2007, along with its two very
> relevant Errata.
>
>
> C) Does DALI 1.2 allow a user to express spherical coordinates or
> geometrical types in non-equatorial frames?
>
> Thanks,
> Alberto
>
>
>
>
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