http://www.et.byu.edu/~beard/papers/preprints/BeardMcLain__.pdf
I've figured out how to find out the instantaneous position of the vehicle.
But Will the direction be the delta of the current position and next position?
I am not sure, is there a reliable way to do it?
Of course, I already have the start direction and some ending directions
in the spirals and straight lines.
For example, when the vehicle starts at radian 4.7, with a left turn
can I assume at time 0, it is at 4.7 and at time 1, it will be at 4.6.....(left-handed system)
The elevation isn't taken into account anyways....
Thanks
Jack