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["T.vanLankveld" <>]

I have tried Exact_predicates_exact_kernel, in which case no errors occur,
but the program does become too slow.


However, I have found another way around the problem: these errors seem to
only occur when the polygons A and B share an edge. Therefore, before doing
a boolean operation, I remove each duplicate edge by creating a helper
polygon that covers the edge and subtracting it from A (I keep track the
part of the helper polygon that was part of polygon A).


an example for symmetric difference is:
"
void symmetric_difference(Polygon_set_2& A, const Polygon_set_2& B) {
        Polygon_set_2 toRemove;

        Arrangement_2 AA = A.arrangement();
        for (Arrangement_2::Edge_iterator it = AA.edges_begin(); it !=
AA.edges_end(); ++it)
                if (contains(B, *it)) {
                        Point_2 s = it->source()->point(), t = 
it->target()->point();

                        Polygon_2 bar;
                        Vector_2 along(s, t);
                        along= 0.05 * (along/ 
CGAL::sqrt(along.squared_length()));
                        Vector_2 perp = along.perpendicular(CGAL::CLOCKWISE);

                        bar.push_back(s-along-perp);
                        bar.push_back(s-along+perp);
                        bar.push_back(t+along+perp);
                        bar.push_back(t+along-perp);

                        Polygon_set_2 rem(bar);
                        rem.difference(A);
                        rem.difference(B);
                        toRemove.join(rem);

                        A.join(bar);
                }

        A.symmetric_difference(B);
        A.difference(toRemove);
}
"

Even though toRemove shares a number of edges with A^B, this does not
produce errors.

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