[postgis-users] polygons inside polygon

[paul.malm at lfv.se]

Thanks Nicolas,
I’ve added a boolean column (outer_pg) in my original layer (org).
Then I tried to populate that column, but it I don’t have the skills…
I tried to use your selection:

SELECT DISTINCT p1.fid, p2.fid IS null AS "outer_pg"
FROM org p1
     LEFT JOIN org p2 ON p1.fid <> p2.fid AND st_within(p1.the_geom, p2.the_geom)
order by p1.fid;

My try to populate outer_pg:
UPDATE org
SET "outer_pg" =  (SELECT outer_p FROM (
SELECT DISTINCT p1.fid, p2.fid IS null AS outer_p
from org p1
     LEFT JOIN org p2 ON p1.fid <> p2.fid AND st_within(p1.the_geom, p2.the_geom) WHERE p1.fid = org.fid) AS tmp)

But that is not correct, do you have any suggestions?
Kind regards,
Paul



Från: postgis-users <postgis-users-bounces at lists.osgeo.org> För Nicolas Ribot
Skickat: den 30 november 2021 19:17
Till: PostGIS Users Discussion <postgis-users at lists.osgeo.org>
Ämne: Re: [postgis-users] polygons inside polygon


Klicka bara på länkar och öppna bilagor om du litar på avsändaren och vet att innehållet är säkert.
Hi,

What about a simple left join on the table searching for polygons contained inside other polygon ?
Polygons that are contained inside other polygons will have false for the outer_pg column and true if they are not contained (ie are outer polygons).
You can then create the tables you want based on the outer_pg values


select distinct p1.id, p2.id is null as outer_pg
from polygon p1
     left join polygon p2 on p1.id <> p2.id and st_within(p1.geom, p2.geom)
order by p1.id;

id       outer_pg
1        true
2        true
3        true
4        true
5        false
6        false
7        false
8        true
9        true
10       true
11       false

Nicolas
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