ha! Neat trick, Brent.
On Mar 10, 2012, at 3:26 PM, pcr...@pcreso.com wrote: > Hi Nicolas, > > Change your SQL to insert a buffered version of your polygon with a buffer > distance of zero. You should get a topologically correct polygon (in this > particular case anyway), which is a tracing of the perimeter with any > duplicate vertices resolved. > > eg: > > insert into test_polygon (id,geometry) values (1,ST_buffer(ST_GeomFromText( > 'POLYGON((...))'),0.0)); > > Cheers, > > Brent Wood > > --- On Sun, 3/11/12, Nicolas Ribot <nicolas.ri...@gmail.com> wrote: > > From: Nicolas Ribot <nicolas.ri...@gmail.com> > Subject: Re: [postgis-users] How to make this invalid polygon valid one > To: "PostGIS Users Discussion" <postgis-users@postgis.refractions.net> > Date: Sunday, March 11, 2012, 9:45 AM > > Hello > > I am trying to create a buffer around my polygon, which unfortunately is not > a valid one. > (reason: "Self-intersection[......]"). > > This polygon is the output of my calculation that creates from a set of > connected edges an area, consisting of all edges located on the border. > > http://postgis.17.n6.nabble.com/file/n4564623/Screen_Shot_2012-03-09_at_10.02.41_PM.png > Polygon image > > can someone tell me, what can I do, to remedy this behavior and to make this > geometry valid > > this are the sql statements to reproduce my problem: > http://postgis.17.n6.nabble.com/file/n4564623/testPolygon.sql > testPolygon.sql > > thanks > > Markus > > > > Hi Markus, > > An attempt with Pgis 1.5.3: > > I saw in a Paul's presentation the power of unioning linestrings together, in > order to generated several line where they intersects > (http://2010.foss4g.org/presentations_show.php?id=3369) > > The goal is to use duplicate points from the initial polygon to allow us to > make the difference between these points and the exterior ring of the > polygon, to generates several linestrings that can be passed to st_buildArea: > > The first part (with...) extracts duplicate points (cf img1) > > with duplicates as ( > select st_collect((st_dumppoints(geometry)).geom) as point > from test_polygon > group by (st_dumppoints(geometry)).geom > having count((st_dumppoints(geometry)).geom)>1 > ) > select st_buildarea ( > st_union(st_difference(st_exteriorRing(t.geometry), point)) > ) from duplicates, test_polygon t; > > The result (img2) is a multipolygon that can be dumped to extract individual > parts, or directly buffered. > (the query is not at all optimized ;) ) > > Nicolas > > -----Inline Attachment Follows----- > > _______________________________________________ > postgis-users mailing list > postgis-users@postgis.refractions.net > http://postgis.refractions.net/mailman/listinfo/postgis-users > _______________________________________________ > postgis-users mailing list > postgis-users@postgis.refractions.net > http://postgis.refractions.net/mailman/listinfo/postgis-users
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