Figure 2

Three examples for the determination of the rotation direction in the cross-section. The lines from the blue point (first) to the red point (second) are pathline segments that are projected into a plane. (a) The successive points are in the first and second quadrant, they represent a right-handed segment. (b) The successive points are in the fourth and third segment, they represent a left-handed segment. (c) The points are in diagonal quadrants, in this case they represent a right-handed segment.