Remove the overlap line left by PostGIS ST_Difference

Question

I need to remove any overlapping from these two polygons when I run

select geometry(ST_Difference(poliA::geometry, poliB::geometry)) 

apparently returns A-B but, if I use ST_Intersection to look for any overlapping area it's returning a line that matches with part of the border where both polygons collide.

select geometry (ST_Intersection( (select geometry(ST_Difference(poliA::geometry, poliB::geometry))),poliB::geometry)

I even tried to remove it using Arcgis Pro altering the xy tolerance but can't get rid of overlapping lines and dots, and ST_Difference is not doing better

Answer 1

This behaviour is expected. If two polygons are adjacent they intersect.

These four grid squares does not overlap, the result of their intersection can be a linestring:

select st_intersection(t1.geom, t2.geom)
from public.grid4 t1
join
public.grid4 t2
on st_intersects(t1.geom, t2.geom)
where t1.id=1 and t2.id=2

Or a point

Check if they overlap with st_overlaps, they dont:

select *
from public.grid4 t1
join
public.grid4 t2
on st_overlaps(t1.geom, t2.geom)
where t1.id=1 and t2.id=2

If you for some reason want to use intersects you can limit the result by st_area or st_dimension:

select  t1.id, 
        t2.id, 
        st_astext(st_intersection(t1.geom, t2.geom)), 
        st_area(st_intersection(t1.geom, t2.geom)), 
        st_dimension(st_intersection(t1.geom, t2.geom))
from newgrid t1
join newgrid t2
on st_intersects(t1.geom, t2.geom)
where t1.id < t2.id
--and st_area(st_intersection(t1.geom, t2.geom))>100
--and st_dimension(st_intersection(t1.geom, t2.geom))=2

Answer 2

The only way I found to solve the problem was using the Reshape tool from Arcgis Pro (Edition module) to cut manually all the overlapping segments. Leaving this comment here in case somebody sees him/herself in this situation.