This is my first post in here so bear with me. I am working on a network generation problem on the earth's surface. In order to generate the network, I have a pair of points (a,b) and a pair of points (c,d). The pair (c,d) represents a line segment for an obstacle on the surface and thus no line segment (a,b) can exist if it crosses line segment (c,d). However, because of the curvature of the earth, this is a pretty difficult problem from what I can tell. Any help would be MUCH appreciated. Thanks in advance.