Question

Im looking for some fairly easy (I know polygon union is NOT an easy operation but maybe someone could point me in the right direction with a relativly easy one) algorithm on merging two intersecting polygons. Polygons could be concave without holes and also output polygon should not have holes in it. Polygons are represented in counter-clockwise manner. What I mean is presented on a picture. As you can see even if there is a hole in union of polygons I dont need it in the output. Input polygons are for sure without holes. I think without holes it should be easier to do but still I dont have an idea.

Answer 1

1. Remove all the vertices of the polygons which lie inside the other polygon: http://paulbourke.net/geometry/insidepoly/
2. Pick a starting point that is guaranteed to be in the union polygon (one of the extremes would work)
3. Trace through the polygon’s edges in counter-clockwise fashion. These are points in your union. Trace until you hit an intersection (note that an edge may intersect with more than one edge of the other polygon).
4. Find the first intersection (if there are more than one). This is a point in your Union.
5. Go back to step 3 with the other polygon. The next point should be the point that makes the greatest angle with the previous edge.