[postgis-devel] Two geometries intersects but intersection is empty

[Pierre Racine]

SELECT st_intersects(geomA, geomB), astext(st_intersection(geomA, geomB))
FROM (SELECT
      st_geomfromtext('POINT(-75.5516150170498 49.2824791927083)',4326) AS geomA,
      geomfromewkb(decode('0103000020e610000001000000050000001c9f33ce69e352c0718f0e9a27a44840e77546654fe352c067d2ad7b35a448406cd4767448e352c0fc7fd3a900a44840a1fd63dd62e352c0073d34c8f2a348401c9f33ce69e352c0718f0e9a27a44840', 'hex')) AS geomB
) foo


>-----Original Message-----
>From: postgis-devel-bounces at postgis.refractions.net [mailto:postgis-devel-
>bounces at postgis.refractions.net] On Behalf Of Paul Ramsey
>Sent: 3 juin 2010 14:26
>To: PostGIS Development Discussion
>Subject: Re: [postgis-devel] Two geometries intersects but intersection is empty
>
>FYI: select encode(asbinary(geom),'hex') from ...
>
>P
>
>On Thu, Jun 3, 2010 at 2:24 PM, Martin Davis <mbdavis at refractions.net> wrote:
>> Pierre, can you provide the second geometry in WKBHex?  I can't read the
>> string that you provided.
>>
>> Pierre Racine wrote:
>>>
>>> Here is the case:
>>>
>>> SELECT st_intersects(geomA, geomB), astext(st_intersection(geomA, geomB))
>>> FROM (SELECT
>>>      st_geomfromtext('POINT(-75.5516150170498 49.2824791927083)',4326) AS
>>> geomA,
>>>      geomfromewkb(E'\\001\\003\\000\\000
>>>
>\\346\\020\\000\\000\\001\\000\\000\\000\\005\\000\\000\\000\\034\\2373\\316i\\343R\\300q\\217\\016\\2
>32\'\\244H@\\347uFeO\\343R\\300g\\322\\255{5\\244H at l\\324vtH\\343R\\300\\374\\177\\323\\251\\000\\244H
>@\\241\\375c\\335b\\343R\\300\\007=4\\310\\362\\243H@\\034\\2373\\316i\\343R\\300q\\217\\016\\232\'\\2
>44H@')
>>> AS geomB
>>> ) foo
>>>
>>> Sorry I can't provide it as wkt as the wkt version return the expected
>>> result (and the wkb version does not (before I read Paul's last FAQ)).
>>>
>>> Pierre
>>>
>>>
>>>>
>>>> -----Original Message-----
>>>> From: postgis-devel-bounces at postgis.refractions.net
>>>> [mailto:postgis-devel-
>>>> bounces at postgis.refractions.net] On Behalf Of Martin Davis
>>>> Sent: 3 juin 2010 12:15
>>>> To: PostGIS Development Discussion
>>>> Subject: Re: [postgis-devel] Two geometries intersects but intersection
>>>> is empty
>>>>
>>>> Can you post the case?
>>>>
>>>> This can happen because the intersects predicate test is more accurate
>>>> than the intersection computation.  (Technically speaking, it's possible
>>>> to detect that two segments intersect, but be unable to compute an
>>>> accurate point that represents the intersection).
>>>>
>>>> Pierre Racine wrote:
>>>>
>>>>>
>>>>> Hi,
>>>>>
>>>>> Is it possible that st_intersects returns true on two geometries but
>>>>> their st_intersection returns
>>>>>
>>>>
>>>> "GEOMETRYCOLLECTION EMPTY"?
>>>>
>>>>>
>>>>> I have a nice case here...
>>>>>
>>>>> Pierre
>>>>>
>>>>> _______________________________________________
>>>>> postgis-devel mailing list
>>>>> postgis-devel at postgis.refractions.net
>>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel
>>>>>
>>>>>
>>>>>
>>>>
>>>> --
>>>> Martin Davis
>>>> Senior Technical Architect
>>>> Refractions Research, Inc.
>>>> (250) 383-3022
>>>>
>>>> _______________________________________________
>>>> postgis-devel mailing list
>>>> postgis-devel at postgis.refractions.net
>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel
>>>>
>>>
>>> _______________________________________________
>>> postgis-devel mailing list
>>> postgis-devel at postgis.refractions.net
>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel
>>>
>>>
>>
>> --
>> Martin Davis
>> Senior Technical Architect
>> Refractions Research, Inc.
>> (250) 383-3022
>>
>> _______________________________________________
>> postgis-devel mailing list
>> postgis-devel at postgis.refractions.net
>> http://postgis.refractions.net/mailman/listinfo/postgis-devel
>>
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