[postgis-users] ST_Intersects and NOT ST_Disjoint aren't equal?

[Gerrit Hoven]

the query:
select ST_AsEWKT(geom) from tbl_surface where
ST_Disjoint(ST_GeomFromText('Polygon((0 0, 9999999 0, 9999999 9999999, 0
9999999, 0 0))'), geom)
thinks that this polygon is outside of this box:
POLYGON((3512977.796 5404487.019 280.571,3512967.71 5404472.11
280.571,3512967.71 5404472.11 243.831,3512977.796 5404487.019
243.831,3512977.796 5404487.019 280.571))



Martin Davis schrieb:
> Can you find a single geometry where NOT ST_Disjoint and ST_Intersects 
> are different?  That will help in debugging this behaviour.
> 
> Gerrit Hoven wrote:
>> Hello Postgis Users
>>
>> I was wondering about the behavior of ST_Disjoint and ST_Intersects.
>>
>> My data is a 3D citymodel which is stored in "tbl_surface". There is 
>> the geometry column "geom".
>> Normally I expect the same behavior of "WHERE ST_Intersects(...)" and 
>> "WHERE NOT ST_Disjoint(...)"
>>
>> But look what happens if I try to get everything inside a huge 
>> boundingbox:
>>
>> Query A:
>> select geom from tbl_surface where 
>> ST_Intersects(ST_GeomFromText('Polygon((0 0, 9999999 0, 9999999 
>> 9999999, 0 9999999, 0 0))'), geom)
>>
>> returns 98524 rows, which I expect because this is all my data and the 
>> boundingbox covers them all
>>
>>
>> Query B:
>> select geom from tbl_surface where not 
>> ST_Disjoint(ST_GeomFromText('Polygon((0 0, 9999999 0, 9999999 9999999, 
>> 0 9999999, 0 0))'), geom)
>>
>> returns: 61895 rows (should be 98524 ???)
>>
>>
>> Query C:
>> select geom from tbl_surface where 
>> ST_Disjoint(ST_GeomFromText('Polygon((0 0, 9999999 0, 9999999 9999999, 
>> 0 9999999, 0 0))'), geom)
>>
>> returns: 36629 rows (should be 0 ???)
>>
>>
>> All my geometries are polygons which have z-coordinates.
>> There exist polygons (like walls), which when projecting them to the 
>> x-y plane, are only lines. I think this is a hint for the strange 
>> behavior of ST_Disjoint. Just look what the query results look like:
>>
>> This is all my data:
>> http://81.89.98.151/Picture/queryA.png
>>
>> This is everything inside the big box, using NOT ST_Disjoint. All the 
>> polygons that are not a line in 2D
>> http://81.89.98.151/Picture/queryB.png
>>
>> This is everything "outside" the big box, using ST_Disjoint. All the 
>> polygons that are lines in 2D
>> http://81.89.98.151/Picture/queryC.png
>>
>>
>> Can anybody explain this to me? Or is it a bug.
>>
>>
>> Regards,
>> Gerrit
>>
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>