title: How to separate touching outlines of areas inside a polygonmesh?
body: <p>I have a 3D polygonmesh, which has some holes in it's surface. I calculated the mean curvature for each node to find the holes and marked the nodes of a hole with a flag. In a second step I looked at the nodes of the holes and collected those, which have neighbours which aren't part of any hole area. That are my outlines.  </p>
  
  <p>Now I see that their are some sort of islands inside a hole. Because of that I've got inner outlines, which sometimes touch each other. (blue lines inside the picture)</p>
  
  <p><img src="https://i.stack.imgur.com/mYJdK.png" alt="Surface holes with borders"></p>
  
  <p>I want to find out which is the outermost border of them. But I don't find a clue how to say for sure at a fork of the border, if I'm going on on the outer line or if I'm entering an inner outline. </p>
  
  <p>I thought about finding the shortest way between fork nodes. But it is possible that their are some huge convexities on my outer border. So this doesn't work.</p>
  
  <p>My second idea was to determine which direction I'm walking, while going from node to node. But I can't get a fixed node in the centre of one hole to compare distances. </p>
  
  <p>Here is some common data about an outline:</p>
  
  <ul>
  <li>one outline can touch multiple other outlines</li>
  <li>another outline can be touched multiple times by the same outline</li>
  <li>an outline is a continuous line </li>
  <li>it must not be circle like shaped</li>
  </ul>
  
  <p>I'm thankful for every hint how too clearly separate the outer line.</p>