[geos-devel] GEOS-3.0.0RC2 Buffer Error

[strk]

Horst, please see this bug item:
http://postgis.refractions.net/bugs/bug.php?op=show&bugid=127

Maybe it explains why 2.2.3 was *succeeding* in cleanups.
You can mimic 2.2.3 behaviour by calling SnapToGrid() prior
to buffer()

--strk;

On Tue, Nov 14, 2006 at 05:01:29PM +0100, Düster Horst wrote:
> Sandro
> 
> Yes you are right. I know there are ring-selfintersections in my
> geometry. With 2.2.3 I used buffer(0) to dissolve these invalid
> geometries. The reason why there are ring-selfintersections and
> selfintersections in this geometry is the way how 
> the swiss landsurvey  model curves etc. They use parts of a circle as a
> special geometry feature. As the result in some cases you will get very
> small polygons with invalid geometries when the geometries are converted
> to simple features. To dissolve these errors 2.2.3 buffer(0) works fine
> for me. 
> 
> You see what I need is a function to clean selfintersections. Do you
> have an idea how I can do that?? Perhaps it is possible to create a
> PostGIS function geomclean()??
> 
> What do you think about that?
> 
> Best regards 
> Horst
> 
> 
> 
> -----Ursprüngliche Nachricht-----
> Von: strk at refractions.net [mailto:strk at refractions.net]
> Gesendet am: Dienstag, 14. November 2006 12:45
> An: geos-devel
> Betreff: Re: [geos-devel] GEOS-3.0.0RC2 Buffer Error
> 
> Oh, btw... your geometry is invalid:
> 
> NOTICE:  Ring Self-intersection at or near point 608038 227925 227925
> 
> It was by luck if it worked with 2.2.3 (maybe an effect of some
> rounding?)
> 
> --strk;
> 
> On Tue, Nov 14, 2006 at 12:40:53PM +0100, strk at refractions.net wrote:
> > On Mon, Nov 13, 2006 at 09:55:32AM +0100, Düster Horst wrote:
> > > GEOS-3.0.0RC2 produces incorrect results when the attached
> shape-polygon
> > > imported to postgis is buffered with an bufferdistance of 0. 
> > > 
> > > 1. Import the shape to PostGIS
> > > 2. Buffer the Polygon with: create table test as select
> > > buffer(the_geom,0) as the_geom
> > > 3. Take a look at the result, you will see incorrect filled areas.
> > > 
> > > The same procedure with GEOS-2.2.3 produces correct results!
> > 
> > Could you also post the *correct* result ?
> > 
> > --strk;
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