[postgis-users] Intersection of three polygons

[Saranya Kuniyil]

For example:
POLYGON((0 0,0 1,1 1,1 0,0 0))   filename as part1
POLYGON((0 0,0 3,3 3,3 0,0 0))   filename as part1
POLYGON((0 0,0 2,2 2,2 0,0 0))   filename as part2
POLYGON((0 0,0 5,5 5,5 0,0 0))   filename as part2
POLYGON((0 0,0 3,3 3,3 0,0 0))   filename as part3
POLYGON((0 0,0 4,4 4,4 0,0 0))   filename as part3

Now I need to find regions which are common in all categories.
that is I expect the result as:
POLYGON((0 0,0 1,1 1,1 0,0 0))
POLYGON((0 0,0 2,2 2,2 0,0 0))
POLYGON((0 0,0 3,3 3,3 0,0 0))



On Mon, Feb 20, 2017 at 3:12 PM, Rémi Cura <remi.cura at gmail.com> wrote:

> 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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>
>
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