computational geometry - finding boundary of the unbounded face of a planar graph

Question

I'm decomposing a planar graph into (degenerate Polygons) which are given by the inner faces. The algorithm I use just walks along the leftmost edge relative to the previous edge (it's a little bit more complicated but not really important). See the link for a small example. My problem is the following: The algorithm also finds the boundary of the unbounded outer face. Therefore I need to find it (if possible fast) and delete the corresponding polygon.

The Problem is essentially the following: given a set of directed edges for which we know that they go around the Polygon clockwise, decide if it is the boundary of the outer face. It seems like it should be easy but I'm really lost.

top left a planar graph, top right directed edges, bottom: boundary of outer and inner face

question from:https://stackoverflow.com/questions/66059993/finding-boundary-of-the-unbounded-face-of-a-planar-graph

Answer 1

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