[postgis-devel] Is this behavior of union by design or a side effect?

[Obe, Regina]

I was testing out st_union trying to figure out its fitness for 3d use
and also comparing to my cascade imp to make sure they agree in cases
before I put in wiki, and noticed I can mix dimensions and get answers
instead of an error like I get with ST_Collect.

I presume this is attributed to the elevation and average elevation
calcs in there.  I'm just not quite sure what to think of this.  Seems a
little odd that you can mix dimensions and if you do, I would think it
would assume z is 0 or something not do some weird averaging.  Well its
always been like this so its not a new thing and probably least of
importance right now.  Just thought I'd point it out before I forget.


SELECT ST_AsEWKT(st_union(the_geom))
FROM
(SELECT ST_GeomFromEWKT('POLYGON((-7 4.2,-7.1 4.2,-7.1 4.3,
-7 4.2))') as the_geom
UNION ALL
SELECT ST_GeomFromEWKT('POINT(5 5 5)') as the_geom
UNION ALL
	SELECT ST_GeomFromEWKT('POINT(-2 3 1)') as the_geom
UNION ALL
SELECT ST_GeomFromEWKT('LINESTRING(5 5 5, 10 10 10)') as the_geom ) as
foo;

--Result

"GEOMETRYCOLLECTION(POINT(-2 3 1),LINESTRING(5 5 5,10 10 10),POLYGON((-7
4.2 5,-7.1 4.2 5,-7.1 4.3 5,-7 4.2 5)))"

Thanks,
Regina
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