[postgis-devel] Z() and M() semantics

strk at refractions.net strk at refractions.net
Wed Nov 23 07:07:35 PST 2005

I committed the change in head.

Another thing. OGC tells X() and Y() are only valid
when called against POINTS.

PostGIS currently tries to find a point in collections
and uses the first one. NULL is also returned when there
is no POINT in the input.

What do you think about raising an error if input is
not a single POINT ?


On Wed, Nov 23, 2005 at 03:29:25PM +0100, Markus Schaber wrote:
> Hi, Strk,
> strk at refractions.net wrote:
> > M() is already in the 1.1 branch.
> > 
> > BTW, what about making Z() and M() return NULL
> > rather then 0 for points w/out the requested dimension ?
> > 
> > I think NULL is the correct semantic, but nobody answered in September:
> > 
> > http://postgis.refractions.net/pipermail/postgis-devel/2005-September/001577.html
> I agree that NULL is the correct semantic, and the old semantic can be
> easily emulated using coalesce(M(point),0) (which is backwards
> compatible with the old semantic, btw).
> Markus
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