I have been doing a bit more research into this and i think that I basically need to know which of the two vectors described by the lines is head. then if the 2nd vector is ahead I use the angle and if the first vector is head I use -angle in the rotation.

I've seen something about using atan rather than acos for vectors in 2D, is it possible to extend this to 3D vectors?

I need to write up my logic on how I have to go the point i am so far for the programs user guide and so when I ahve done that I will upload it to give more details on the logic I have followed so far.

Regards

Robyn