Handling of Z-coordinates by geometry functions is underspecified

[FransKnibbe]

Geometry functions like geof:buffer and geo:convexHull ignore Z-coordinates (as per SFA-CA). but GeoSPARQL does not say how this influences generated output Geometry. Are Z-coordinates completely absent from output? Or are they all set to 0?

[VladimirAlexiev]

@FransKnibbe Since current GeoSPARQL is 2.5D, aren't there other functions with a similar concern?

• Eg what do intersects, difference, symDifference do to Z?
• You mention convexHull, surely the same applies to concaveHull?
• And their 2 agg* variants: see make more parallels of spatial aggregate functions to normal functions #483
• (On the other hand, I assume that union and aggUnion leave Z in place)