Appropriate UCD for (Cartesian) unit vectors on the celestial sphere

[James Tocknell]

Hi Baptiste

The specific survey I'm looking at is the 6dF Galaxy Survey, specifically
the CX, CY and CZ columns in the TARGET table which is documented at
http://www-wfau.roe.ac.uk/6dFGS/target.html (other tables in the survey
also use the same CX, CY, CZ, but TARGET is the simplest and the
documentation for the columns is identical). I'd naively expect to
translate those columns as something like
pos.celestial;phys.vector.unit;pos.cartesian.{x,y,z}, but I can't see a UCD
to represent a unit vector nor a UCD for something using celestial
coordinates (pos.geocentric could work instead of pos.celestial, but
representing unit vectors doesn't seem possible currently). I'm inclined to
use meta.cryptic for now, unless someone has a better suggestion?

James

On Fri, 25 Oct 2019 at 19:06, Baptiste Cecconi <ceccobapts at yahoo.fr> wrote:

>
> Le 22 oct. 2019 à 07:20, James Tocknell <james.tocknell at mq.edu.au> a
> écrit :
>
> Hi everyone
>
> I'm currently defining UCDs for a survey we're ingesting, and came across
> something that stumped me.  There are three rows representing the x,y,z
> coordinates of the unit vector on the celestial sphere. There does not
> appear to be anything appropriate to represent these columns (`pos.cartesian`
> is close but doesn't include the spherical nature of this system). Any
> suggestions for what UCD should be used?
>
> Thanks
> James
>
>
> Hi James,
>
> First, new UCDs for pos.spherical (and associated standard axes) are
> arriving in the upcoming version UCD 1.4.
> Then, indeed I'm not sure how to set the UCD for your example. Could you
> be more specific, with a more extended example ?
>
> Baptiste
>
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