[postgis-users] ST_UNION drops M coordinate

[Satish Murthy]

Thanks Paul. 

I also noticed that some other functions too have this limitation (such as ST_CONTAINS). Is there a table/matrix somewhere that lists which function supports XYZM?

Satish

> Date: Wed, 5 Aug 2009 10:36:46 -0700
> From: pramsey at opengeo.org
> To: postgis-users at postgis.refractions.net
> Subject: Re: [postgis-users] ST_UNION drops M coordinate
> 
> Yes, we just don't support the higher dimension in the operation. GEOS
> was extended to 3 dimensional handling some time ago, but never got
> pushed farther when we added M at postgis 1.0. Probably fixable, but
> with a reasonable amount of careful work to catch every case.
> 
> P
> 
> On Wed, Aug 5, 2009 at 10:22 AM, Satish Murthy<satish_m at hotmail.com> wrote:
> >
> > 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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