Star-shaped polygon

A star-shaped polygon (top). Its kernel is shown at the bottom in red. A star-shaped polygon (not to be confused with star polygon) is a polygonal region in the plane that is a star domain, that is, a polygon that contains a point from which the entire polygon boundary is visible. Formally, a polygon P is star-shaped if there exists a point z such that for each point p of P the segment zp lies entirely within P. The set of all points z with this property (that is, the set of points from which all of P is visible) is called the kernel of P.