[postgis-users] Intersection of three polygons

[Rémi Cura]

Hey,
sorry to say it's very difficult to understand what you want to do.
Please either do a schema or a precise description (with math: you have
setA, set B, setC , and you want to find ...).
Cheers,
Rémi-C

2017-02-20 5:57 GMT+01:00 Saranya Kuniyil <saranyak578 at gmail.com>:

> Hi all,
> I am new to postgis and I need to find intersection of three polygons.
> In my table named "mytable" contains large no of polygon coordinates and
> grouped into three categories by adding a field called "filename".I
> labelled the category names as part1, part2, part3 in filename . Now I need
> to find all polygon which spacially intersect in three categories.
> I write my code as:
>  SELECT ST_Intersection(a.geom, b.geom) as intersect_ab
> FROM mytable a INNER JOIN mytable b ON ST_Intersects(a.geom,b.geom) INNER
> JOIN mytable c ON ST_Intersects(a.geom,c.geom)
> WHERE ST_Overlaps(a.geom, b.geom) AND ST_Overlaps(b.geom, c.geom) AND
> ST_Overlaps(a.geom, c.geom) AND ST_isvalid(a.geom)='t' AND
> ST_isvalid(b.geom)='t' AND ST_isvalid(c.geom)='t' AND a.filename = 'part1'
>    AND b.filename = 'part2' AND c.filename = 'part3') ;
> Is it correct?????
>
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