title: How do i decide edges of a general polygon?
body: <p>I want to retrieve <strong>all the edges</strong> of a general polygon, which is described by some 2 dimensional vertexes.</p>
  
  <p>I thought a method to getting all possible combinations and testing if it is intersecting with others at none-vertex point.</p>
  
  <p>But there was a problem, if the polygon is <strong>concave</strong>, we cannot test whether it is the non-edge combination.</p>
  
  <p>How can I do this properly?</p>