Hi Barend,

That is correct. If you mean "cutting a ring with a segment": it can be used/implemented, discussed and described on the GGL-mailing list. That might be useful for you as well. It is described here:
<http://boost-geometry.203548.n3.nabble.com/Understanding-get-turns-for-linestring-polygon-overlay-td2397891.html>

I meant intersection of ring border and segment. For example.

ring: (0, 0), (2, 0), (2, 2), (0, 2)

segment: (-1, 1), (3, 1)

output two points: (0,1) and (2,1)

There is distance algorithm between point and segment (or ring), is it possible to get closest point of segment to that point?

No, or not yet. I once needed that and created a strategy for that, but it is not in the Trunk or Release (not even in the extensions). I will see if it can be added, because there has been a question about this earlier.

It would be nice to see such usage of strategy in the documentation.

Best Regards,

Sergey