[postgis-users] Re: truly_inside

[Juanse]

Thanks to all of you !! ... and people says Opensource have no "support",
ja!

the simple && solutions works great.

I will try a benchmark against mapinfo intersect, after running the more
sofisticated solution with the gist index.

Juanse
temuko-chile



----- Original Message -----
From: David Blasby <dblasby at refractions.net>
To: <postgis-users at postgis.refractions.net>
Sent: Monday, October 21, 2002 2:17 PM
Subject: Re: [postgis-users] Re: truly_inside


> Juanse wrote:
>
> > Is the distance() method too slow, i am runnig
> >
> > select count(*) t0,t1 where distance(t0.wkb_geomtry, t1.wkb_geometry)= 0
and
> > (t0.nombre = 'Galvarino')
> >
> > and it takes for ages
> >
> > t0 have 31 records
> > t1 have 1321 records
>
> try an:
> explain select count(*) t0,t1 where distance(t0.wkb_geomtry,
t1.wkb_geometry)= 0
> and
> (t0.nombre = 'Galvarino')
>
> you're probably doing a full join - thats 40,000 distance() calculations!
>
> You can do this to use an index and speed things up considerably:
>
> SELECT ... FROM t0,t1 WHERE t0.wkb_geometry && t1.wkb_geometry
>             AND distance(t0.wkb_geomtry, t1.wkb_geometry)= 0
>
> This will first ensure that the geometry's bounding boxes intersect (&&),
then
> do the expensive distance calculation.
>
> Dont forget to make a GiST index on t0 and t1.
>
> dave
>
>
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