[postgis-users] Check geometry for true intersection using ST_Relate

strk strk at keybit.net
Mon Jul 19 09:00:09 PDT 2010

On Sun, Jul 18, 2010 at 12:44:37PM +0200, Andrea Peri 2007 wrote:
> Hi,
> I need to retrieve from a table all the geometry that intersect a given 
> polygon .
> But the standard ST_Intersection is no good for me because it return 
> true even if
> two geometry are only touching on their boundary without having a 
> partially overlap each other.
> I don't find other type of intersection that don't responde true on touch.
> So I try to use the ST_Relate(..)
> But I don't understand exactly how define the matrix to use.
> I don't sure if the correct matrix to declare is this
> String overlaps = "T********";
> or this
> String overlaps = "2********";
> my geometry are all polygon so perhaps declaring
> String overlaps = "T********";
> can be sufficient ?

No, T is not sufficient as it'll return you the case
in which intersection is a 1-dimension (line) geometry.
You want 2 (areal) intersection between interiors.


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