“…We are interested in finding conditions on a positive number ε to ensure that the closed r-ball (or a subset of it) centered at p and of radius ε either intersects X or does not intersect X. Indeed, this turns out to be useful in practical applications, for instance, in the setting of the Hough transform, a standard technique to detect curves in images (e.g., see [2], [16], [17], [18]), or for evaluating the performance of robots that are required to follow a desired reference path (see [13]), or even in the field of robot motion planning (see [3]).…”