[postgis-users] Problem with Contains/Within using shapes created by GeomUnion
Mike Leahy
mgleahy at alumni.uwaterloo.ca
Tue Mar 21 09:12:17 PST 2006
Ok, thanks.
Is there anything else I should do then (e.g., make bug report), or
should I just leave it to the experts?
I did find that intersecting the original shape with the unioned shape
produced a polygon similar to the original shape (see below), which I
guess is obvious given nature of the problem. I suppose as a
workaround, I can update the geometry for shape #725 with the trimmed
down intersected shape - though I imagine altering the original shapes
isn't the preferred solution.
test=# select gid, contains(the_geom,intersection(gu,the_geom)) from
gutest cross join (select geomunion(the_geom) as
gu from gutest) as u;
gid | contains
-----+----------
508 | t
17 | t
741 | t
195 | t
725 | t
18 | t
(6 rows)
strk at refractions.net wrote:
> 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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