Saturday, January 11, 2014

Algorithm to sort edge list of simple polygon for 2D and 3D

Sometimes it is handy to sort an edge list. In this case I needed an algorithm to test for concavity of a simple 3D polygon with just one face. You can also apply the procedure on 2D because it just sorts an edge list that could contain either 2D or 3D vertices.

The polygons were made in Blender v.2.67, so the script had to be written in Python and executed via the Run Script button in the text editor. I didn't want to use fancy algorithms to sort edges because we're dealing with simple polygons, so I ended up writing my own. As a side note, the edge-angle checkbox in Blender, which can be used to see if a polygon is convex or concave didn't work for me, so I had no other choice but to first sort edges before I can apply angle calculations on consecutive vertices. Suggestions for improvements are welcome and hopefully it helps someone else who had to deal with the same (or similar) issues in Blender!