[postgis-users] error in isvalid function

[strk at refractions.net]

On Fri, Nov 05, 2004 at 11:42:46AM +0300, ksa wrote:
> okay, hole is really invalid. But how I can handle of this situation? If I
> *already* have polygones with similar holes. Which function I can use to
> determinate this without getting an exception?

Problem is that the invalidity of that geometry prevents 
POSTGIS->GEOS conversion.
GEOS refuses to build a polygon *that* invalid...
Maybe the postgis geos wrapped could consider that as an invalidity,
do people see any drawbacks in this ?

--strk;

> 
> > I've verified your query.
> > The Polygon is actually invalid due to degenerate hole (as the
> > exception states).
> > When extracting the rings, these are handled as LINESTRINGS, for which
> > the degenerate case is not checked.
> > Which do you think would be a better handling of this situation ?
> >
> > --strk;
> >
> >
> >
> > On Fri, Nov 05, 2004 at 09:17:01AM +0300, ksa-nil5 wrote:
> > > >> Hi, all!
> > > >>
> > > >> I'm working with follow data (POLYGON):
> > > >>
> > > >> POLYGON((37.654639 55.726496,37.654056 55.726947,37.653801
> 55.727333,37.653801 55.727435,37.654468 55.727483,37.656654
> 55.727466,37.656572 55.727063,37.656654 55.726713,37.657052
> 55.726531,37.657571 55.726365,37.658071 55.725961,37.658321
> 55.725609,37.658303 55.725374,37.658321 55.725609,37.658906
> 55.725309,37.659488 55.72511,37.658135 55.724571,37.657386
> 55.724922,37.657135 55.724873,37.65647 55.725274,37.655635
> 55.725828,37.655195 55.7265,37.655635 55.725927,37.654639
> 55.726496),(37.658321 55.725609,37.658906 55.725309,37.659488
> 55.72511,37.658906 55.725309,37.658321 55.725609))
> > > >>
> > > >> search=# select isvalid(geometryFromText(the_geom));
> > > >> NOTICE:  IllegalArgumentException: degenerate ring (does not contain
> 3 distinct points)
> > > >> ERROR:  GEOS isvalid() threw an error!
> > > >>
> > > >> search=# select isvalid(exteriorring(geometryFromText(the_geom)));
> > > >>  isvalid
> > > >> ---------
> > > >>  t
> > > >> (1 row)
> > > >>
> > > >> search=# select isvalid(interiorringN(geometryFromText(the_geom),1));
> > > >>  isvalid
> > > >> ---------
> > > >>  t
> > > >> (1 row)
> > > >>
> > > >> Any suggestions?
> > > >>
> > > >> Thanks!
> > > >>
> > > >> Sergey Karin
> > > >
> > > >What GEOS / PostGIS version are you using ?
> > > >
> > > >SELECT postgis_full_version();
> > > >
> > > >--strk;
> > > >
> > >
> > > search=# select postgis_full_version();
> > >                                         postgis_full_version
> >
> > --------------------------------------------------------------------------
> ---------------------------
> > >  POSTGIS="0.9.0" GEOS="2.0.1" PROJ="Rel. 4.4.8, 3 May 2004" USE_STATS
> DBPROC="0.0.1" RELPROC="0.0.1"
> > > (1 row)