Ah, I see the problem. The polygon that you provide is not a valid
polygon (It only has 2 unique points, so really it's a line segment
masquerading as a polygon). The spatial predicates are only guaranteed
to work with valid geometries as input - they may give incorrect answers
if the input is invalid.
The reason ST_intersects works for all cases is that intersection can be
determined without requiring topological validity for most simple cases
(which this certainly is). I think PostGIS may contain optimizations
for ST_intersects which are not present for ST_disjoint (although they
should be....), and these are determining the correct answer.
So use ST_intersects!
Gerrit Hoven wrote:
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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--
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022
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