* pos -- (x, y) position of the seat relative to the centre of the vehicle.
x and y may be numbers from approximately -1.0 to 1.0. They will be
multiplied by the approximate_radius of the vehicle.
* pos -- (x, y) position of the seat relative to the centre of the vehicle.
x and y may be numbers from approximately -1.0 to 1.0. They will be
multiplied by the approximate_radius of the vehicle.