[postgis-users] st_equals strangeness

[Sufficool, Stanley]

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: postgis-users-bounces at postgis.refractions.net
> [mailto:postgis-users-bounces at postgis.refractions.net] On
> Behalf Of William Temperley
> Sent: Friday, January 08, 2010 7:28 AM
> To: postgis-users at postgis.refractions.net
> 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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