Right, this: select 'yes' as foo from table1 a, table1 b where a.gid=4 and b.gid=4 and st_intersects(a.the_geom, b.the_geom)
seems likely to a LOT less common than select 'yes' as foo from table1 a, table1 b where a.gid=4 and st_intersects(a.the_geom, b.the_geom) and the latter gets far less benefit from the a.getpoint(0) = b.getpoint(0) test, though the test would still be run on every candidate. I'm not sure where the cost/benefit inflection point is, but I know identity is a pretty rare case. P. On 2/18/08, Martin Davis <[EMAIL PROTECTED]> wrote: > There's some new code on the way in GEOS and PostGIS which will improve > the performance of this case. Bu it won't be anywhere near as fast as > your proposed check for an identical start point. > > The "identical start point" check is great for the particular case of > comparing identical polygons. But it does nothing for the general > case. The question is: is the identical compare case common enough > that it's worth adding in this check for all cases? > > Willy-Bas Loos wrote: > > Hi, > > > > I´ve noticed that intersect(a,b) is slow when i compare a (nice and > > large) geometry with itself. > > so the syntax is: > > > > select 'yes' as foo > > from table1 a, table1 b > > where a.gid=4 > > and b.gid=4 > > and intersects(a.the_geom, b.the_geom) > > > > This particular polygon has about 10 000 points, and the query runs > > for 4 whole seconds. > > At the first point that is being compared, however, PostGIS should > > notice that it has a "positive". > > > > I´m only using postgis 1.0, so this migt have been changed allready. > > Has it? > > > > WBL > > > > ------------------------------------------------------------------------ > > > > _______________________________________________ > > postgis-users mailing list > > [email protected] > > http://postgis.refractions.net/mailman/listinfo/postgis-users > > > > -- > Martin Davis > Senior Technical Architect > Refractions Research, Inc. > (250) 383-3022 > > _______________________________________________ > postgis-users mailing list > [email protected] > http://postgis.refractions.net/mailman/listinfo/postgis-users > _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
