title: How to determine a diagonal is in or out of a concave polygon?
body: <p>The diagonal (a diagonal is a segment connecting nonadjacent vertices) of a concave (non-convex) polygon can be completely in or out of the polygon(or can intersect with the edges of polygon). How to determine whether it is completely in the polygon?(<strong>a method without point-in-polygon test</strong>).</p>