Anti st_union

[Bob Pawley]

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Hi

 

In order to have only one row, I have a number of points  stored in a table as st_union.

 

Is there a method of breaking the points out of  the st_union geometry so that I can access the points individually.

 

I want to use the points as a reference for st_within. It doesn't seem to works as it seems to regard the st_union point geometry as a whole.

 

Bob

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[Maxime van Noppen]

Bob Pawley wrote:

> Hi
>  
> In order to have only one row, I have a number of points  stored in a
> table as st_union.
>  
> Is there a method of breaking the points out of  the st_union geometry
> so that I can access the points individually.
>  
> I want to use the points as a reference for st_within. It doesn't seem
> to works as it seems to regard the st_union point geometry as a whole.

Hi,

That depends of the type of the resulting geometry. If it is a
MultiPoint (which it likely is if you ST_Union-ed points) you should
look at the ST_Dump function :

http://postgis.refractions.net/documentation/manual-1.4/ST_Dump.html

--
Maxime
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[Simon Greener-3]

Bob,

> In order to have only one row, I have a number of points  stored in a table as st_union.

I assume you mean stored in a table as a MULTIPOINT geometry?

> Is there a method of breaking the points out of  the st_union geometry so that I can access the points individually.
>
> I want to use the points as a reference for st_within. It doesn't seem to works as it seems to regard the st_union point geometry as a whole.

Here is an example of what I think you want using 10 points dynamically generated, unioned and then Dumped.

select (ST_Dump(MPoint)).geom as Point
   from (select ST_Union(ST_Point(g.*,g.*)) as MPoint
           from generate_series(1,10,1) g
        ) as m;

Or

select ST_GeometryN(f.MPoint,f.pcount) as Point
   from (select m.MPoint, generate_series(1,ST_NumGeometries(m.mpoint),1) as pcount
           from (select ST_Union(ST_Point(p.*,p.*)) as MPoint from generate_series(1,10,1) as p ) m
        ) as f;

regards
Simon
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