title: How do I extract the edges from a segment delaunay graph in CGAL?
body: <p>I need to find the medial axis of a concave polygon with holes. I'm using <a href="http://www.cgal.org/" rel="nofollow noreferrer">CGAL</a>. My current approach is:</p>
  
  <ol>
  <li>Build the <a href="http://doc.cgal.org/latest/Segment_Delaunay_graph_2/index.html#Chapter_2D_Segment_Delaunay_Graphs" rel="nofollow noreferrer">2D segment delaunay graph</a> of the polygon</li>
  <li>Extract the resulting output segments (bisectors)</li>
  <li>Test each segment to find if it's inside the polygon</li>
  <li>The resulting set of segments will form the medial axis of the polygon</li>
  </ol>
  
  <p>I can build the SDG, and testing edges should be straight forward but I'm struggling to extract the edges of the SDG, or the corresponding Voronoi graph rather. There should be a few types of edges I'd expect: points, lines and parabolas.</p>
  
  <p>How do I do this? Am I even on the right track?</p>
  
  <p>Also I know I can iterate through the edges of the graph using one of the supplied methods and I understand this returns the face and opposite vertex to the edge. But how do I use this to get, say, the endpoints of a bisecting line?</p>