Algorithm to find intersections between polylines

Question

Bentley-Ottmann algorithm works for finding intersections of set of straight lines. But I have lot of polylines:

Answer 1

The sweep line algorithm has a nice theory but is hard to implement robustly. You need to treat vertical segments, and there might be cases where more than two line segments intersect in a single point (or even share a common line segment).

I'd use an R-Tree to store bounding boxes of the line segments of the polyline and then use the R-Tree to find possibly intersecting elements. Only these need to be tested for intersection. The advantage is that you can use a separate R-Tree for each polyline and thus avoid detection of selfintersections, if needed.

Consider using CGAL's exact predicates kernel to get reliable results.