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ivoa-std / CoordinateDM

Astronomical Coordinates and Coordinate Systems Data Model
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AstroCoordSystem #10

Open pahjbo opened 2 years ago

pahjbo commented 2 years ago

In the model AstroCoordSystem both is a CoordSys and contains a collection of CoordSys - I am not sure that this is really meaningful for an AstroCoordSystem to derive from CoordSys - could an AstroCoordSystem contain an AstroCoordSystem?

mcdittmar commented 2 years ago

The AstroCoordSystem contains a collection of PhysicalCoordSys (eg: GenericSys + TimeSys + SpaceSys + etc ). It is not allowed to contain AstroCoordSystem.

This hierarchy allows all Coordinate-s to have a single relation to the associated coordinate system (ie: a single vodml-id (Coordinate.coordSys)

Where the model is now, you may be right, that there is no meaningful reason for AstroCoordSystem to derive from CoordSys. The current configuration is consistent with STC-1 and, If I recall correctly, this was useful in the version of this model which allowed construction of multi-dimensional coordinates whose axes were in different domains.