[mods: I posted this a few days ago, and that post was acknowledged etc (it was my first post as a new subscriber) but I haven't receieved a copy myself and cannot find it in the archives - perhaps I should be more patient?] Hello, I'm hoping to use boost voronoi to construct the (internal) medial axis for closed shapes (with holes). I need to work out which vertices of the voronoi are inside, outside and on a boundary. So my first goal is to determine which vertices correspond to the ends of the input segments (boundary vertices). The way I do this at the moment, is to look at each edge and test if its source vertex, vertex0(), is equal to either end point of the segment contained by the edge's cell. (1) If it is then it's a boundary vertex otherwise it's not. Is that correct? (2) When comparing a vertex with an input point can I do an exact compare (==) or should I use a tolerance (epsilon)? Thanks, fuzzy.