[postgis-users] Problem with Contains/Within using shapes created by GeomUnion

[strk at refractions.net]

Sorry, I didn't notice the attachment.
I gave a look at it now, and I confirm the bug.
Having tried against current JTS (1.7.1) I can say the same bug is there.
This is probably another example of binary predicates working at
virtually infinite precision vs. constructive functions (geomunion)
applying a precision model.

See this thread on geos-devel:
http://geos.refractions.net/pipermail/geos-devel/2006-March/001841.html

--strk;

On Mon, Mar 20, 2006 at 03:08:33PM -0500, Mike Leahy wrote:
> strk:
> 
> I'm not fully sure what should put in a self-contained test case - but
> if you use load sample shapes table I sent in my previous message
> (gutest.sql.zip - attached again to this message), then you can run all
> of the queries I mentioned earlier.  I also tried the dropbbox function
> (see below), which produces the same result.  Let me know if there's
> anything more I can do here.
> 
> Mike
> 
> On my winxp machine:
> createdb -U postgres test
> psql -U postgres -f ../share/contrib/lwpostgis.sql test
> psql -U postgres -f ../share/contrib/spatial_ref_sys.sql test
> psql -U postgres -f <path_to>/gutest.sql test
> psql -U postgres test
> 
> test=# select gid, contains(dropbbox(gu),dropbbox(the_geom)) from gutest
> cross join (select geomunion(dropbbox(the_geom)) as
> gu from gutest) as u;
>  gid | contains
> -----+----------
>  508 | t
>   17 | t
>  741 | t
>  195 | t
>  725 | f
>   18 | t
> (6 rows)
> 
> test=# select version();
>                                          version
> ------------------------------------------------------------------------------------------
>  PostgreSQL 8.1.1 on i686-pc-mingw32, compiled by GCC gcc.exe (GCC)
> 3.4.2 (mingw-special)
> (1 row)
> 
> test=# select postgis_full_version();
>                                postgis_full_version
> ----------------------------------------------------------------------------------
>  POSTGIS="1.1.1" GEOS="2.2.1-CAPI-1.0.1" PROJ="Rel. 4.4.9, 29 Oct 2004"
> USE_STATS
> (1 row)
> 
> strk at refractions.net wrote:
> > There might be a bug in the computed bounding box of your geometries,
> > Try to run the within and contains against a dropbbox() version
> > of the input. If the problem persist, please provide a small
> > self-contained testacase so we can check against different
> > versions and architectures.
> > 
> > TIA
> > 
> > --strk;
> > 
> > On Fri, Mar 17, 2006 at 01:47:58PM -0500, Mike Leahy wrote:
> >> Hello list,
> >>
> >> I'm wondering if I've run into a bug with PostGIS (or maybe the GEOS 
> >> module).  I've been building a set of management areas that are created 
> >> from a series of smaller districts merged together.  I would normally 
> >> expect the resulting merged polygon to topologically contain all of its 
> >> constituent polygons.  This has proved to be true in all cases for my 
> >> data except one (so far).  You can see the results of a test query below 
> >> that compares a handful of shapes to their geomunion'd shape.  In all 
> >> cases except the shape with ID# 725, it looks fine.  For some reason, a 
> >> geomunion of that shape with the other contiguous shapes will no longer 
> >> contain the original shape itself according to the contains() or 
> >> within() functions.  I've looked at this shape using Qgis and compared 
> >> it to the corresponding geomunion shape, and it looks fine as far as I 
> >> can tell visually.
> >>
> >> I've included a dump of a test table containing the six shapes in this 
> >> management area used in the queries shown below.  Let me know if there's 
> >> anything I can do to work around this problem, or if there's any 
> >> additional information I should provide.
> >>
> >> Mike
> >>
> >> ===========================================================
> >>
> >> testdb=# select gid, contains(u,the_geom), within(the_geom,u), 
> >> isvalid(the_geom) as the_geom_isvalid, isvalid(u) as u_isvalid, 
> >> contains(the_geom,the_geom) as the_geom_contains_itself from gutest 
> >> cross join (select geomunion(the_geom) as u from gutest) as foo;
> >>  gid | contains | within | the_geom_isvalid | u_isvalid | 
> >> the_geom_contains_itself
> >> -----+----------+--------+------------------+-----------+--------------------------
> >>  508 | t        | t      | t                | t         | t
> >>   17 | t        | t      | t                | t         | t
> >>  741 | t        | t      | t                | t         | t
> >>  195 | t        | t      | t                | t         | t
> >>  725 | f        | f      | t                | t         | t
> >>   18 | t        | t      | t                | t         | t
> >> (6 rows)
> >>
> >>
> >> testdb=# select version();
> >>                                                           version
> >> ----------------------------------------------------------------------------------------------------------------------------
> >>  PostgreSQL 8.1.3 on i386-redhat-linux-gnu, compiled by GCC 
> >> i386-redhat-linux-gcc (GCC) 4.1.0 20060210 (Red Hat 4.1.0-0.24)
> >> (1 row)
> >>
> >> testdb=# select postgis_full_version();
> >>                                postgis_full_version
> >> ----------------------------------------------------------------------------------
> >>  POSTGIS="1.1.1" GEOS="2.2.1-CAPI-1.0.1" PROJ="Rel. 4.4.9, 29 Oct 2004" 
> >> USE_STATS
> >> (1 row)
> > 
> > 
> >> _______________________________________________
> >> postgis-users mailing list
> >> postgis-users at postgis.refractions.net
> >> http://postgis.refractions.net/mailman/listinfo/postgis-users
> > 
> > 


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