title: Funnel Algorithm finding the optimal path through a polygon
body: <p>I would like to get the shortest path through a polygon. My inputs are a start point, a destination point and a list of vertices of my polygon. 
  I was searching the web and I found following sites describing the Funnel algorithm:
  <a href="http://ahamnett.blogspot.co.at/2012/10/funnel-algorithm.html" rel="nofollow">1</a>, <a href="http://digestingduck.blogspot.co.uk/2010/03/simple-stupid-funnel-algorithm.html" rel="nofollow">2</a>, <a href="https://skatgame.net/mburo/ps/thesis_demyen_2006.pdf" rel="nofollow">3</a>. 
  I tried to implement the algorithm from number <a href="https://skatgame.net/mburo/ps/thesis_demyen_2006.pdf" rel="nofollow">3</a>. But there are many questions coming up to understand the listing right. I do not know which angle has to be calculated in function Add. 
  I do not know what the FunnelDeque ApexType is. 
  So my questions are: Exists there an easy implementation of this Funnel Algorithm? 
  If no, how can I implement the Algorithm from <a href="https://skatgame.net/mburo/ps/thesis_demyen_2006.pdf" rel="nofollow">3</a>, getting an useable result.</p>