[postgis-devel] polygonize_garray build invalid geometries
strk at refractions.net
strk at refractions.net
Mon Jan 3 09:47:32 PST 2005
I've made polygonize(geom) aggregate return GEOMETRYCOLLECTION.
Polygon construction issue is still open as are all the
multiGEOM constructors (should they check validity?)
--strk;
On Mon, Jan 03, 2005 at 04:57:25PM +0100, strk at refractions.net wrote:
> The problem here is in the implementation of the postgis polygonize
> interface. GEOS polygonize returns a list of polygons, not a
> multipolygon. Postgis is *forcing* single-geometry output, creating
> a multipolygon, which probably often results in an invalid geometry.
>
> I think the fix here is creating a collection, instead of a MultiPolygon.
> Note that in this case postgis lacks a polygon construction mean.
>
> I suggest make_polygon(geometry, geometry[]), having shell as first
> argument and a list of holes as second (optional) argument.
>
> --strk;
>
> On Sun, Jan 02, 2005 at 12:01:35PM -0500, Carl Anderson wrote:
> > against CVS Postigs and CVS GEOS
> >
> > polygonize_garray in instances returns invalid geometries
> >
> > test cases avail at
> > http://wms.co.fulton.ga.us/data/postgis/polygonize_error.sql.gz
> > (sorry, it was too big for the list)
> >
> > run the script to build object then
> >
> > select isvalid(the_geom) from polygonize_error;
> >
> > select
> > isvalid(polygonize_garray(array_append('{}',
> > intersection(boundary(the_geom),boundary(the_geom))
> > )))
> > from polygonize_error;
> >
> > intersection(boundary(),boundary()) -- converts all rings into simple
> > linestrings (actually OGC line geometries SFSSQL 2.1.6)
> > _______________________________________________
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> > postgis-devel at postgis.refractions.net
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>
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