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

Paul Ramsey pramsey at opengeo.org
Thu Jun 3 11:25:48 PDT 2010


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\\232\'\\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\'\\244H@')
>> 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
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>>
>>
>
> --
> 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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