&& 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?
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