[postgis-users] ST_within bug?

[Johannes Sommer]

Ok, thank you for the clearing answers.


Paul Ramsey schrieb:
> Right, so you're seeing very slight coordinate drift. Probably Kosmo 
> is inserting the object as hex-encoded WKB, and then your other 
> application is pulling WKT, which is ever-so-slightly different than 
> the underlying binary. The only way to avoid drift and precision 
> issues is to get both applications using exactly the same 
> representation, preferably the more exact WKB ones.
>
>
>
> On Feb 13, 2008, at 12:14 PM, Johannes Sommer wrote:
>
>> Hi Paul,
>>
>> The update worked. Now I get the correct boolean values. But my 
>> problem is not solved.
>> As I wrote the problem is that the Desktop Client tries to insert a 
>> geometry object as GeometryFromText in a way that results in a 
>> slightly different binary geometry object.
>>
>> example:
>> application (Kosmo) insert:
>> 7;"0103000020EC7A000001000000060000007101EE208F2E51416E <----
>> 252C38668A5441320DDB8DF62F514174604A3E2E8A544154E6C014F52F514164A38519888A54418CAB1FB4132F5141C4<--- 
>>
>> F318A8BB8A54415<---
>> 36F90B2A62E514125384224A18A54417101EE208F2E51416E252C38668A5441"
>>
>> after update in psql-terminal (ST_GeomFromText...):
>> 7;"0103000020EC7A000001000000060000007001EE208F2E51416D <----
>> 252C38668A5441370DDB8DF62F514176604A3E2E8A54414FE6C014F52F514163A38519888A54418CAB1FB4132F5141C2<--- 
>>
>> F318A8BB8A54414<---
>> E6F90B2A62E514129384224A18A54417001EE208F2E51416D252C38668A5441"
>>
>>
>> I'm not sure, but I think Kosmo uses "GeometryFromText" (I have asked 
>> the list for this).
>> I could not reproduce the reaction in a psql terminal with 
>> "GeometryFromText". If I do the INSERTS on the terminal, I get the 
>> correct results.
>>
>> Can this happen if one uses (GeometryFromText, SRID) instead of 
>> (ST_GeomFromText, SRID) in an application with JDBC-Driver?
>>
>> thanks,
>> Johannes
>>
>>
>> Paul Ramsey schrieb:
>>> I think your geometries have slightly different topology than your 
>>> text representations admit. I cannot reproduce your result, but then 
>>> I started from your text representations.
>>>
>>> Do this:
>>>
>>> update test set geometry = 
>>> ST_GeomFromText('POLYGON((4506577.35665529 
>>> 5381992.48407281,4506597.92548351 5381745.65813424,4506999.01763368 
>>> 5381784.22468715, 4506834.46700796 5382069.61717861,4506615.92320819 
>>> 5382085.04379977,4506577.35665529 5381992.48407281))', 31468) where 
>>> t_id = 3;
>>>
>>> And then see what happens.
>>>
>>> On Feb 13, 2008, at 3:44 AM, Johannes Sommer wrote:
>>>
>>>> Hi,
>>>>
>>>> I ve got a problem with the ST_Within() function. It does not 
>>>> always return correct answers.
>>>>
>>>> SELECT AsText(geometry) FROM test WHERE t_id=3;
>>>> -->result:
>>>> "POLYGON((
>>>> 4506577.35665529 5381992.48407281,
>>>> 4506597.92548351 5381745.65813424,
>>>> 4506999.01763368 5381784.22468715,
>>>> 4506834.46700796 5382069.61717861,
>>>> 4506615.92320819 5382085.04379977,
>>>> 4506577.35665529 5381992.48407281))"
>>>>
>>>> -- (WKT/WKB):
>>>> SELECT ST_Within(ST_GeomFromText('POLYGON((
>>>> 4506577.35665529 5381992.48407281,
>>>> 4506597.92548351 5381745.65813424,
>>>> 4506999.01763368 5381784.22468715,
>>>> 4506834.46700796 5382069.61717861,
>>>> 4506615.92320819 5382085.04379977,
>>>> 4506577.35665529 5381992.48407281))', 31468), a.geometry) FROM test 
>>>> a WHERE t_id=3;
>>>>
>>>> -->result: false (but obviously it should be true)
>>>>
>>>> -- (WKT/WKT):
>>>>
>>>> SELECT ST_Within(ST_GeomFromText('POLYGON((
>>>> 4506577.35665529 5381992.48407281,
>>>> 4506597.92548351 5381745.65813424,
>>>> 4506999.01763368 5381784.22468715,
>>>> 4506834.46700796 5382069.61717861,
>>>> 4506615.92320819 5382085.04379977,
>>>> 4506577.35665529 5381992.48407281))', 31468), (SELECT 
>>>> AsText(geometry) FROM test WHERE t_id=3));
>>>>
>>>> --> result:
>>>> ERROR: Operation on two geometries with different SRIDs
>>>> KONTEXT: SQL function "st_within" statement 1
>>>>
>>>> Ok - I understand this reaction, because AsText returns no SRID.
>>>>
>>>> -- (WKT/WKT):
>>>> SELECT ST_Within((select st_astext(geometry) FROM test WHERE 
>>>> t_id=3), (SELECTst_astext(geometry) FROM test WHERE t_id=3));
>>>>
>>>> -->result: true (as it should be)
>>>>
>>>> -- (WKB/WKB):
>>>> select st_within((SELECT geometry FROM test WHERE t_id=3), (SELECT 
>>>> geometry FROM test WHERE t_id=3));
>>>> -->result: true (correct)
>>>>
>>>> SELECT ST_Within((select st_astext(geometry) FROM test WHERE 
>>>> t_id=3), (SELECTst_astext(geometry) FROM test WHERE t_id=3));
>>>>
>>>> So the problem is that the Desktop Client tries to insert a 
>>>> geometry object as GeometryFromText / ST_GeomFromText / GeomFromText
>>>> and I have to compare this new geometry object with an existing 
>>>> Polygon.
>>>>
>>>> It makes no difference if I use _st_within / st_within / within, 
>>>> geometryfromtext / st_geomfromtext / geomfromtext or astext / 
>>>> st_astext.
>>>>
>>>> I used:
>>>> -Windows XP, "POSTGIS="1.3.1" GEOS="3.0.0rc4-CAPI-1.3.3" PROJ="Rel. 
>>>> 4.5.0, 22 Oct 2006" USE_STATS",
>>>> "PostgreSQL 8.2.5 on i686-pc-mingw32, compiled by GCC gcc.exe (GCC) 
>>>> 3.4.2 (mingw-special)"
>>>>
>>>> -Linux, "POSTGIS="1.3.2" GEOS="3.0.0rc5-CAPI-1.4.0" PROJ="Rel. 
>>>> 4.6.0, 21 Dec 2007" USE_STATS",
>>>> "PostgreSQL 8.2.6 on i686-pc-linux-gnu, compiled by GCC gcc (GCC) 
>>>> 4.2.1 (SUSE Linux)"
>>>>
>>>> Where am I going wrong?
>>>>
>>>> regards,
>>>> Johannes
>>>>
>>>>
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