[postgis-users] how to create ouline of multiple objects

[G. van Es]

Leo/Paul,

Indeed, a bunch of polygons (900) of wich I need the outline. In fact drawing one line around the objects. 

I tried st_union but this returns an empty result.
st_exteriorRing returns lines from polygons but still the same number of objects.

Might be close to it but I'm still struggling with it.

Ge


--- On Thu, 8/13/09, Paragon Corporation <lr at pcorp.us> wrote:

> From: Paragon Corporation <lr at pcorp.us>
> Subject: Re: [postgis-users] how to create ouline of multiple objects
> To: "'PostGIS Users Discussion'" <postgis-users at postgis.refractions.net>
> Date: Thursday, August 13, 2009, 11:54 AM
> Ge,
> 
> What do you mean by outline of all objects?  You
> mean  if you have a bunch
> of polygons you just want one record with all boundaries
> dissolved?
> 
> Maybe you are looking for ST_Union
> 
> SELECT ST_Union(the_geom)
> FROM sometable
> 
> That will dissolve boundaries.
> http://postgis.refractions.net/documentation/manual-svn/ST_Union.html
> 
> or you mean you have a polygon and you want the linestring
> outline.
> 
> For that use ST_Boundary(the_geom) or ST_ExteriorRing
> http://postgis.refractions.net/documentation/manual-svn/ST_Boundary.html
> 
> http://postgis.refractions.net/documentation/manual-svn/ST_ExteriorRing.html
> 
> 
> 
> Leo 
> 
> -----Original Message-----
> From: postgis-users-bounces at postgis.refractions.net
> [mailto:postgis-users-bounces at postgis.refractions.net]
> On Behalf Of G. van
> Es
> Sent: Thursday, August 13, 2009 2:48 PM
> To: PostGIS Users Discussion
> Subject: [postgis-users] how to create ouline of multiple
> objects
> 
> Hi All,
> 
> Maybe a stupid question but I have a shape imported in PG
> of wich I want to
> determine the outline of all objects. The result should be
> a LINE or just
> one POLYGON.
> 
> Does anyone know if this is possible in PG.
> 
> Thanks,
> 
> Ge
> 
> 
>       
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