Just for fun, I am working on a little side-project: As a first step, I want to be able to build a grid-based world (think Dungeon Keeper), generate a nav-mesh for this world and then let agents wander around it. I've already done plenty of googling and ended up following the instructions given in the answer to this gamedev question: How can I generate a navigation mesh for a tile grid?
Now, I've completed step 1 in that I now have iso-lines representing the outlines of the walkable area. This could look like this:
The blue lines are the generated outlines of the walkable area. As you can see, in this case there is one walkable areas defined by two lines because the area is a circle.
This is where I'm stuck: If it were a regular polygon I'd probably be able to implement some sort of triangulation algorithm (there's plenty of examples on the net, I guess), but how do I go about this case? Do you have any pointers for me?