Given a point P(x1,y1,z1) in 3D space and its orientation what would be the co-ordinates of other end of the line of length L, if it starts at P(x1,y1,z1). The rotation of point P(x1,y1,z1) takes place about its local axis.
Kindly read the links I gave on your previous post, as it is essentially the same question.
You'll need to construct a rotation matrix for the orientation and then do something like:
P2 = P1 + mat * (0, 0, L)