Hi Paul,

I should have defined my terms; As I understand it a vector has a direction and a magnitude, in this case it would be a heading and a distance. A 2D waypoint would be a pair of coordinates representing a point on some grid or other, in my case a Cartesion grid with the positive x-axis lying along the magnetic North, and the origin (0,0) located at the robot's Home position.(recharging station).

As it moved away from its home position it could record its movements as a series of vectors

e.g 82(cm), @45(deg)

34, 134

150, 89

or it could record the turning points

e.g. 0,0

33,33

187,63

The components of the vectors would be gotten from a magnetic compass and wheel encoder

The waypoints would be calculated from the vectors.

As I write this I have a stronger and stronger feeling that the two methods would be equally error prone since one can be derived from the other, but I also know that "feeling" that you are right is no proof that you are.