Ok. I see. But why is the results so different. When using ST_Intersects the result is correct, while using && it seems there is no order in which vector grid cells it selects. It is not the cells intersecting with the country polygon, but rather a mesh of random cells also outside of the country polygons.
2010/9/22 Paragon Corporation <[email protected]> > && does a bounding box intersects check where as ST_Intersects does a > more intensive actual geometry intersect check. Which is why its slower. > > > > ------------------------------ > *From:* [email protected] [mailto: > [email protected]] *On Behalf Of *Andreas Forø > Tollefsen > *Sent:* Wednesday, September 22, 2010 11:00 AM > *To:* PostGIS Users Discussion > *Subject:* [postgis-users] Difference between ST_Intersects and && > operator > > Hi all. > I am working on a huge vector grid project where i need to intersect > country polygon data and vector grid cells. > For this i need to first select the grid cells which intersects with the > country polygons. > > SELECT DISTINCT testgrid.gid, xcoord, ycoord, cell INTO testgrid2 FROM > testgrid, cshaperef WHERE ST_Intersects(cshaperef.the_geom, > testgrid.cell)=true > > I tried both the ST_Intersects and the && operator, but i cannot really > understand the difference. > After looking at my results the ST_Intersects gave exactly the cells which > intersected with the country polygons, while the && gave many additional > cells. > Another interesting observation is the the && is way faster than the > ST_Intersects which in my case 188 polygons and 212000 cells takes a lot of > time. > > Could anyone please elaborate on the difference? > > > _______________________________________________ > postgis-users mailing list > [email protected] > http://postgis.refractions.net/mailman/listinfo/postgis-users > >
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