For a tube simulation I am doing I am working with circular coordinates. I.e. a point on the wall of the tube could be defined by two parameters: the point along the centerline (spline) of the tube, and the angular coordinate given in the range [0,1].
Because the angular coordinate 1 describes a full rotation, 1 = 0; (because 360 degrees will give the same result as 0 degrees rotation)
This leads to a couple of issues if we want to calculate the difference between two angular coordinates, or the mean between two angular coordinates.