[postgis-devel] Issue 148 in postgis: st_touches doesn't work as it should on st_touches(line,point)

codesite-noreply at google.com codesite-noreply at google.com
Wed Apr 8 08:57:49 PDT 2009

Comment #2 on issue 148 by ke... at refractions.net: st_touches doesn't work  
as it should on st_touches(line,point)

Regina, you are correct.

Another way to state the relation is:
Geometry (a) touches geometry (b) if and only if:
1. the intersection of (a) and (b) is not the empty set (which means they  
have to
interact somehow) AND
2. the intersection of the interior of (a) and the interior of (b) is not  
the empty set.

This means that intersection must occur on the boundary of at least one of  
geometries.  Since, according to the specs, a point does not have a  
boundary (only an
interior), if follows that ST_Touches returns true only if the point lies  
on the
boundary (or endpoints) of the line.

-- Kevin

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