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

[Martin Davis]

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
>>>
>>> _______________________________________________
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>>>
>>>
>>>       
>> --
>> Martin Davis
>> Senior Technical Architect
>> Refractions Research, Inc.
>> (250) 383-3022
>>
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>>     
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>   

-- 
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022