Which of the following statements regarding autonomous agricultural vehicles and path-tracking algorithms (such as the Pure Pursuit and Stanley controllers) is/are CORRECT?
Options:
(A) In Pure Pursuit tracking, the steering angle command is calculated by fitting a circular arc from the vehicle rear axle to a look-ahead target point on the path
(B) Increasing the look-ahead distance in Pure Pursuit controller dampens lateral oscillations but slows convergence to the desired path
(C) Stanley controller incorporates both heading error and lateral cross-track error measured at the front axle
(D) Pure Pursuit tracking becomes unstable as look-ahead distance approaches infinity
Answer Key:
A, B, C
Step-by-Step Solution & Explanation
- **A is correct:** Pure Pursuit geometry calculates curvature $\kappa = \frac{2\sin\alpha}{L_d}$ to reach a point at look-ahead distance $L_d$ on the reference line.
- **B is correct:** A larger look-ahead distance produces sluggish, smooth cornering with zero overshooting, whereas smaller $L_d$ causes aggressive tracking and potential oscillations.
- **C is correct:** The Stanley method (developed for Stanford's autonomous vehicles) combines front-wheel heading error with non-linear cross-track error feedback: $\delta(t) = \psi(t) + \tan^{-1}\left(\frac{k e(t)}{v(t)}\right)$.
- **D is incorrect:** As look-ahead distance approaches infinity, path curvature $\kappa \to 0$, causing the steering angle to asymptotically approach zero (driving straight ahead), not unstable divergence.