[postgis-users] Problems with ST_Within in an island of a multipolygon

[Larry Reeder]

Anybody have any ideas on this one?    Do you think I should post it
to the developer list?

Thanks........            Larry

On Fri, Mar 18, 2011 at 8:43 AM, Larry Reeder <lnreeder at gmail.com> wrote:
> I have a layer called "foo" of about 5000 polygons.   One of the
> polygons is a multipolygon with island shells.  ST_Within isn't
> working as expected for points within that island shell.
>
>
> Here's my table:
>
> foo_spatial=# \d foo
>                              Table "public.foo"
>  Column  |   Type   |                        Modifiers
> ----------+----------+---------------------------------------------------------
>  gid      | integer  | not null default nextval('foo_gid_seq'::regclass)
>  the_geom | geometry |
> Indexes:
>    "foo_pkey" PRIMARY KEY, btree (gid)
>    "foo_the_geom_key" gist (the_geom)
> Check constraints:
>    "enforce_dims_the_geom" CHECK (st_ndims(the_geom) = 2)
>    "enforce_geotype_the_geom" CHECK (geometrytype(the_geom) =
> 'MULTIPOLYGON'::text OR the_geom IS NULL)
>    "enforce_srid_the_geom" CHECK (st_srid(the_geom) = (-1))
>
>
> ST_Within returns true when asked if a point inside the island belongs
> to the polygon that contains the island:
>
> foo_spatial=# select ST_Within(ST_GeomFromText('POINT (-115.04252
> 36.05137)', -1), the_geom) from foo where gid = 4933;
>  st_within
> -----------
>  t
> (1 row)
>
> However, when I ask if any polygons contain this point, I don't get any back:
>
> foo_spatial=#  SELECT gid from foo where
> ST_Within(ST_GeomFromText('POINT (-115.04252 36.05137)', -1),
> the_geom);
>  gid
> -----
> (0 rows)
>
>
> Does this make sense?    I know PostGIS can handle the general problem
> of ST_Within for island sub-polygons because when I extract this
> multipolygon into a separate table by itself, the queries work as
> expected.  There seems to be something happening with other polygons
> in the layer that is breaking this.   Initially I did have some bad
> polygons in the layer, but I used the cool script here:
> http://linfiniti.com/2010/07/cleaning-geometries-inside-postgis/.
> That fixed my bad polygons, and now all polygons are valid:
>
> foo_spatial=# select count(*) from foo where ST_IsValid(the_geom) = 'f';
>  count
> -------
>     0
> (1 row)
>
>
> But still ST_Within isn't working as expected.   Here's my version info:
>
> foo_spatial=# select version();
>                                                       version
> ---------------------------------------------------------------------------------------------------------------------
>  PostgreSQL 8.4.7 on x86_64-pc-linux-gnu, compiled by GCC gcc-4.4.real
> (Ubuntu/Linaro 4.4.4-14ubuntu5) 4.4.5, 64-bit
> (1 row)
>
> foo_spatial=# SELECT postgis_full_version();
>                                         postgis_full_version
> -------------------------------------------------------------------------------------------------------
>  POSTGIS="1.5.1" GEOS="3.2.0-CAPI-1.6.0" PROJ="Rel. 4.7.1, 23
> September 2009" LIBXML="2.7.6" USE_STATS
> (1 row)
>
> dash_spatial=# select count(*) from foo where ST_IsValid(the_geom) = 'f';
>  count
> -------
>     0
> (1 row)
>
>
> Anyone have any ideas?
>
>
>
> Thanks............                            Larry
>