[postgis-users] ST_UNION drops M coordinate

[Satish Murthy]

When I do this (notice the second ST_COLLECT):
select ST_AsEWKT (ST_COLLECT (geom)) from (
		select (ST_DUMP(geom)).geom from (select p_geom as geom from (
			select ST_COLLECT (geom_col, st_GeomFromEWKT('Point(1 -1 0 10)')) as
p_geom from tab) a
		)as b ) as c
I get:
    "MULTIPOINT(71.1 -42.31 10 10,1 -1 0 10,1 -1 0 10)"
This is fine, except that "1 -1 0 10" gets repeated.
 
BUT---
When I do (I use ST_UNION here):
select ST_AsEWKT (ST_COLLECT (geom)) from (
		select (ST_DUMP(geom)).geom from (select p_geom as geom from (
			select ST_UNION (geom_col, st_GeomFromEWKT('Point(1 -1 0 10)')) as p_geom
from tab) a
		)as b ) as c
I get this:
   "MULTIPOINT(1 -1 0,71.1 -42.31 10)"
No repetition, but the M coordinate is missing.
 
Any pointers on what's going wrong here?


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