[postgis-devel] ST_UnaryUnion vs ST_Dump + ST_Union

Sandro Santilli strk at keybit.net
Sun Oct 2 06:30:29 PDT 2011

On Sun, Oct 02, 2011 at 03:25:38PM +0200, Sandro Santilli wrote:

> > In order to node a LineString with selt-intersections, I still have
> > to use st_union (point, geom) because st_unaryunion does not node
> > self-intersection lines.
> It should! Please file a ticket for this one.

Oops, I was wrong.
>From the JTS manual:

<< UnaryUnion always operates on the individual components of
   MultiGeometries. So it is possible to use it to "clean" invalid
   self-intersecting MultiPolygons (although the polygon components must
   all still be individually valid.) >>

Self-intersecting lines aren't really invalid (as per OGC specs) but I 
guess the same applies. We should really hide noding behind a special
function for it. See http://trac.osgeo.org/postgis/ticket/1206


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