Suppose S and A show a square and a set involves the points inside the S, respectively. Moreover, B is a set that involves points outside the S. Let E is a subset of A that includes edge/boundary points. Actually, the edge points are the nearest points in A to the points in B.
I want to know, how does the E or a another subset of A that includes E can be determined based just on A without exhaustive search on A. I mean, does exist a geometric solution for this. For example, maybe it's possible to find a circle with radius r inside the square S that involves the points set named C. Obviously C is a subset of A. So, we can say that E is a subset of A-C.