[postgis-users] Difference between ST_Intersects and && operator

[Andreas Forø Tollefsen]

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 <lr at pcorp.us>

>  && does a bounding box intersects check where as ST_Intersects does a
> more intensive actual geometry intersect check.  Which is why its slower.
>
>
>
>  ------------------------------
> *From:* postgis-users-bounces at postgis.refractions.net [mailto:
> postgis-users-bounces at postgis.refractions.net] *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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