Extracting coordinate pairs of crossing points of two polygons in PostGIS

Is it possible to extract x,y-coordinate pairs of crossing points of two overlapping polygons in PostGIS?

Suppose there are only 2 overlapping points of the polygons the ST_Intersection function extracts more than two coordinate pairs (also the shared vertices of polygons are included).

SELECT ST_Intersection(geometry geomA , geometry geomB);

I am interested only in the 2 boundary crossing points of polygons.

1 Answer 1


Here is one method that'll work with basic polygons (no inner rings)

        ST_Boundary(ST_GeomFromText('POLYGON((0 0, 0 1, 1 1, 1 0, 0 0))')), 
        ST_Boundary(ST_GeomFromText('POLYGON((0.5 0.5, .5 1.5, 1.5 1.5, 1.5 0.5, 0.5 0.5))'))

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