[postgis-users] relationship functions not working well
woklist at kyngchaos.com
Fri Dec 5 15:41:43 PST 2008
On Dec 5, 2008, at 5:19 PM, Obe, Regina wrote:
> What does ST_Intersects + ST_Relate give you and timing.
> That's the one I was interested in if that is faster than
> && + ST_Relate
> In theory those 2 should give you the same answer.
Yes, I get the same features returned, but it's slower, as I expected:
large area: 15448 polys, 7924.840 ms
About as much slower, but a little better, as the difference between
intersects time and && time - I took some more times to get an
average, and the intersect time was a little faster than my first
&& average: 380 ms
intersect average: 1100 ms
&& + relate average: 7200 ms
intersect + relate average: 7900 ms
> -----Original Message-----
> From: postgis-users-bounces at postgis.refractions.net on behalf of
> William Kyngesburye
> Sent: Fri 12/5/2008 5:34 PM
> To: PostGIS Users Discussion
> Subject: Re: [postgis-users] relationship functions not working well
> From what I read in the docs, Intersects first checks the bbox, then
> does the full intersect test. While && just does a bbox test.
> && + st_relate gives me what I want, && only gets the touch-only
> neighboring polys I don't want (and seems to be more rigorous in that
> respect than intersects).
> Some times - the full database has 625396 polygons (that's all the
> SWBD files).
> * a 1 degree selection (an island tile)
> st_intersects only: 216 polys, 494.855 ms
> && only: 219 polys, 12.765 ms
> && plus st_relate: 207 polys, 189.360 ms
> * a 58x13 degree rectangle (many tiles empty - alaska region)
> st_intersects only: 15469 polys, 1460.344 ms
> && only: 15479 polys, 379.317 ms
> && plus st_relate: 15448 polys, 7217.592 ms
> This agrees with what I said about && doing a bbox test only. And
> verifies my guess that larger areas would get real slow.
William Kyngesburye <kyngchaos*at*kyngchaos*dot*com>
All generalizations are dangerous, even this one.
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