Your ascii art doesn't render correctly with fixed font, unfortunately. Anyway I think I understood the issue.
I belive the problem is with mix of dimensions. A line has 1 dimension only, by definition. If we had to make "space" to subtract the points that compose that line, how much space would those points take ? Points have even less dimension: 0... It's like subtracting points from an area and expecting to see holes in it. Does it sound ? --strk; On Fri, Sep 27, 2013 at 02:52:42PM +0200, Rémi Cura wrote: > hey, > I'm experiencing a strange behavior with ST_SymDifference > :<http://postgis.net/docs/manual-2.0/ST_SymDifference.html> > > When doing symdiff of a line and a surface, I get the same surfaces with > added points on surfaces boundary (where line crossed surface). > > Example : > ___________ > *├---------┤* > ------------------- > > gives > ___________ > *| |*** > ------------------- > > I read the SQL MM definition > (here<http://jtc1sc32.org/doc/N1101-1150/32N1107-WD13249-3--spatial.pdf>, > page 67-68-69), and I found no trace of behavior with line against > surfaces. > > Mathematically , if we take for definition the union without the > intersection, the result is false (no point on the line should be in the > result, yet they are). > > I was expecting as output one polygon each side of the line (ie 2 polygons). > > I would appreciate any thoughts about this. > Cheers, > > Rémi-C > PS : I know I can use ST_Split or other tricks for the same result in this > simple case, but not so easily for trickier case. _______________________________________________ postgis-users mailing list [email protected] http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users
