direction

Note, this does NOT ensure that the Z axis twist is taken into account. Most of the time you will want to use direction (Vector3,Vector3) instead, which DOES adjust the z axis twist.

Rotates according to normal, but the z Axis twist is also adjusted according to direction along.

Imagine holding a gun pointing straight upwards. Now rotate your arm, so that the gun points forwards. The butt is pointing downwards.

Start with the gun pointing straight upwards again, but now rotate your shoulder, so that the gun points to the side. The butt now points forwards. Rotate your shoulder again, so that the gun points forwards. This time the butt is pointing to the side, not downwards. So if we only specify the final direction (which was forwards in both cases), this does NOT determine the twist of the gun (the direction of the butt). This example shows that direction (Vector3) isn't sufficient in some cases. We also have to say which direction we are travelling in (along), as well as the direction of the cross sections's normal.

normal decides on the angle that the next crossSection. When using followPath, this will be a 'mitre' joint (i.e. the angle between the previous point and the next point in the path is halved).

along adjusts the z axis twists. When using followPath, this is always the vector between the current point, and the previous point.