DECEMBER 2022 * IEEE ROBOTICS & AUTOMATION MAGAZINE * 61 1.5 2 0.5 1 (a) −0.5 −1.5 −1 −2 1.5 2 0.5 1 (b) −0.5 −1.5 −1 −2 1.5 2 0.5 1 (c) −0.5 −1.5 −1 −2 01 23 X (m) 01 23 X (m) Ground Truth 0123 X (m) 100 150 200 250 300 50 100 150 200 250 300 50 50 100 150 200 250 300 350 400 Time (s) 50 100 150 200 250 300 350 400 Time (s) 50 100 150 200 250 300 350 400 Time (s) 20 40 60 −60 −40 −20 100 150 200 250 300 50 Electric + IMU + Dynamic IMU + Dynamic Electric + IMU 20 40 60 −60 −40 −20 50 100 150 200 250 300 350 400 Time (s) 20 40 60 −60 −40 −20 50 100 150 200 250 300 350 400 Time (s) Figure 9. Experiment 3: Position tracking of a free-swimming robot under our three localization methods. From top to bottom: (a) Architecture 1, (b) Architecture 2, (c) Architecture 3. (Left column) The robot's trajectories of the ground truth (black dotted lines), the estimated trajectories under the " electric sense + IMU + dynamic-model " method (red lines), the " electric sense + IMU " method (blue lines), and the " IMU + dynamic-model " method (yellow lines). (Middle column) The position errors compared to the ground truth. (Right column) The orientation errors compared to the ground truth. 50 100 150 200 250 300 350400 Time (s) Y (m) Y (m) Y (m) Position Error (cm) Position Error (cm) Position Error (cm) Orientation Error (°) Orientation Error (°) Orientation Error (°)