Marking up HEALPix index columns in VOTable

[Walter Landry]

Mark Taylor <M.B.Taylor at bristol.ac.uk> wrote:
>> On Thu, Aug 11, 2016 at 04:03:37PM +0200, Marco Molinaro wrote:
>> > if the order is what is needed,
>> > considering the MOC standardization to be in place,
>> > I vote for a solution that is a part of Rick's suggestion
>> > 
>> > N -> pos.healpix;meta.number
>> > 
>> > into a table level PARAM.
>> > Maybe mixed to a single addition to UCD words:
>> > 
>> > meta.order
>> > 
>> > if we want some more specific detail and a reusable word.
>> > (thus going pos.healpix;meta.order)
>> > 
>> > However I must say that I'm working on a tableset that,
>> > if it were to return such field, would have a non-homogeneous
>> > order for tessellation. But this case is not covered by the
>> > "horrible" solution either.
>> 
>> If I understand correctly what your problem is, I'd say it'd be
>> solved by what I think we need anyway to allow multiple healpix
>> columns (and hence potentially multiple orders) per table: some form
>> of grouping.
> 
> While I can see that it's not impossible in principle to have
> multiple columns using HEALPix indices with different orders
> in a single table, I'm struggling to think of any physical 
> situation where that would be a desirable/meaningful thing to do.

I could see a case where you have different types of spatial indices.
So one column could be HEALPix and another column is q3c or htm.

Cheers,
Walter Landry