[postgis-users] Finding polygones with 'holes' inside

Stephan Holl stephan.holl at intevation.de
Thu Jul 10 05:05:53 PDT 2008


I like to accomplish the task of finding polygons with holes inside
(the table is a MULTIPOLYGON). 
I tried to use ST_nrings, but I am not sure it this always only finds
polygons with wholes inside or also islands, which should be also rings
by definition.

So a 

SELECT gid, name FROM table WHERE ST_nrings(the_geom) > 1;

does not only
find whole polygons, but also polygons with more than one polygon.

PostGIS 1.3.3 with PG 8.3.3

Is there an option to identify 'holes' within polygons directly?



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