DALI v1.2: shape vs ESO and ALMA

[Gregory MANTELET]

Hi Alberto,


On 01/12/2023 13:42, alberto micol 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


I agree with you on this point. I also wondered the same thing: why 
`shape` is limited to only a small part of all available geometries 
being described in DALI?


> 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.


You're right and I, personally, did not forget your talk in Bologna. 
Should we add to the next DAL running meeting a discussion on polygon in 
DAL ecosystem? It would be an occasion to start fixing some of the 
standards referring or badly defining polygons.

My guess is that DALI should replace STC in the future....but it is not 
yet the case, which leads to an unstable and uncomfortable situation on 
some aspects like polygons.


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


As far as I know, no. But I let any DALI author properly answer this 
question.


Cheers,
Grégory
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