Translations:Assembly3 ConstraintPointOnLine/6/en

Point elements have no stretch in any direction (zero length) and so there's no orientation detectable i.e. their ICS are only to match other elements' settings. The orientation of the ICSs always stays the same as the global coordinate system's orientation and can not be used to reduce any degrees of freedom related to rotation. Straight elements have an origin and a direction which is represented by the ICS's z-axis. A direction of the x- and y-axis is not detectable and so rotation around the z-axis can not be used to reduce DOFs. (It doesn't apply in combination with point elements anyway...)