[postgis-devel] ST_UnaryUnion vs ST_Dump + ST_Union

Sandro Santilli strk at keybit.net
Sun Oct 2 06:25:38 PDT 2011

On Sun, Oct 02, 2011 at 01:29:07PM +0200, Jose Carlos Martinez Llario wrote:
> Dear List,
> ┬┐What are the differences between an st_unaryunion and a normal
> union aggregate with the dump geometries from the geom?
> I just could see that the order of the generated segments change.
> What am I missing?

UnaryUnion uses an index to merge nearby components first, reducing
the working and robustness issues earlier.

> 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.


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