Is it really possible to have the following expression evaluate to true?
st_asbinary(n1.geom) = st_asbinary(n2.geom) and !(n1.geom = n2.geom)
That seems completely impossible to me. Rounding errors arise from arithmetic
operations, and there should be no arithmetic operations, only assignment, in
the computation of bounding box.
Sufficool, Stanley wrote:
n1.geom = n2.geom is not binary equal, it is bounding box equal which may
include rounding errors?
st_asbinary(n1.geom) = st_asbinary(n2.geom) is binary equal
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On
Behalf Of William Temperley
Sent: Friday, January 08, 2010 7:28 AM
To: [email protected]
Subject: [postgis-users] st_equals strangeness
Dear all,
Given two points with exactly the same coordinates that are
binary equal (geom = geom), I don't understand how st_equals
can return false.
The following statement:
select
st_astext(n1.geom),
st_astext(n2.geom)
from nodes n1, nodes n2
where (n1.node_id = n2.node_id)
and (not st_equals(n1.geom, n2.geom)) and n1.geom = n2.geom;
yields:
st_astext | st_astext
------------------------------------------+-------------------
----------
------------------------------------------+-------------
POINT(28.291805 37.0481949999918) | POINT(28.291805
37.0481949999918)
POINT(28.291805 37.0481949999918) | POINT(28.291805
37.0481949999918)
POINT(28.2538598984633 37.006806) |
POINT(28.2538598984633 37.006806)
POINT(28.0726373735563 37.022361) |
POINT(28.0726373735563 37.022361)
Could anyone shed any light on this please?
POSTGIS="1.4.1" GEOS="3.1.1-CAPI-1.6.0" btw.
Thanks
Will
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