Getting graph lengths from image junctions with opencv

Question

This question is built off of this other question. Assuming I have a stable junction algorithm implemented. I am trying to derive a graph from the junctions.

I am stuck on: How do I move along a line in openCV and calculate the path length?

So for example when evaluating point C:

C connects with:

• The junction A and has a path length of 20 pixels
• The junction D and has a path length of 112 pixels
• The junction F and has a path length of 30 pixels
• The endpoint E and has a path length of 45 pixels

Thanks