If you include elevation then you have to include tolerance for deviation. I live in an old house, so I can't even walk across the room without a vertical devia

If you include elevation then you have to include tolerance for deviation. I live in an old house, so I can't even walk across the room without a vertical deviation of some sort :) Edit: My point here is that if you try to plot a literal straight line through 3D space, it will be necessary to allow some amount of deviation in one axis. Else your longest 3D line will be the distance between your first two points.