max angular sampling (write-up outline)

our scan line (radius) may fall between pixels, then in the sense of NN,

1. starting with a reference point A
2. evenly sample
3. can't predict the shape of the edge, so consider the worst case: the next edge point can be within one of the 8-neighbors.
4. which one of the 8-nb, determined by the orientation of the radius, position of the anchor point.