[postgis-users] Merge lines

[Picavet Vincent]

Hello,

> Does this look correct?
> 
> select st_linemerge(st_collect(cs1.the_geom))
> from (
> 	select the_geom, st_startpoint(cs_s.the_geom) as linepoint
> 	from mylinetable cs_s
> 	UNION ALL 
> 	select the_geom, st_endpoint(cs_e.the_geom) as linepoint
> 	from mylinetable cs_e
> 
> ) as cs1
> group by linepoint
> having count(*) = 2

Be careful with group by linepoint, as it uses the = operator, which
works on bounding boxes and not on geometries.
The bounding box of a point is not equal to the point itself. This could
lead to points being very close to each other being grouped by, while
being different.
If you want to group by strictly identical geometries, you could do a 
group by st_asbinary(linepoint)

Hope this helps,
Vincent


> 
> 
> > -----Original Message-----
> > From: postgis-users-bounces at postgis.refractions.net
> > [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of 
> > Martin Fafard
> > Sent: Tuesday, October 06, 2009 11:21 AM
> > To: PostGIS Users Discussion
> > Subject: [postgis-users] Merge lines
> > 
> > 
> > Hi
> > 
> > Is there a way to merge lines that are contiguous but stop 
> merging at 
> > an intersection?
> > I have join an image.
> > Thank you
> > 
> > Martin F
> > 
> _______________________________________________
> postgis-users mailing list
> postgis-users at postgis.refractions.net
> http://postgis.refractions.net/mailman/listinfo/postgis-users
>