[postgis-users] ST_Touches and line segment

Martin Davis mbdavis at refractions.net
Thu Mar 19 10:24:14 PDT 2009

I've had some thoughts that it would be nice to extend the concept of 
Intersection Matrix Pattern to allow OR combinations of patterns.  This 
seems to indicate that it's also necessary to be able to specify 
different patterns for different combinations of geometry dimension.

Perhaps a syntax like:

"PP:***-*1*-*** LL:1***-***-*** PL:***-1**-***"

The LP pattern can be automatically inferred from this.

Note that I'm also using a "dashed triplet" syntax, which is more 
readable than a solid string of 9 chars (think phone numbers or IP 

Kevin Neufeld wrote:
> Martin Davis wrote:
>> Kevin Neufeld wrote:
>>> If you have overlapping polygons then use ST_Relate with a custom 
>>> matrix.  IE. ST_Relate(g1, g2, '****1****') will return TRUE for all 
>>> geometry pairs where the intersection of the boundaries occur on a 
>>> line (1).
>> You need to know the type of the input geometries.   The above 
>> pattern will work for polygons, but not for lines.  The L/L and P/L 
>> situation require different patterns:
>> L/L: 1********
>> P/L: ***1*****
> Ah, yes, of course :)
> The symmetric relation is also true:
> L/P: *1*******
> -- Kevin
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Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022

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