This paper presents a performance comparison of different estimation and prediction techniques applied to the problem of tracking multiple robots. The main performance criteria are the magnitude of the estimation or prediction error, the computational effort and the robustness of each method to non-Gaussian noise. Among the different techniques compared are the well known Kalman filters and their different variants (e.g. extended and unscented), and the more recent techniques relying on Sequential Monte Carlo Sampling methods, such as particle filters and Gaussian Mixture Sigma Point Particle Filter.
Table 1: Summary of Bayesian prediction techniques compared in the present work.
Initial state estimate:
x^0=E[x0]
Initial state covariance:
P0=E[(x0−x^0)(x0−x^0)T]
Process noise covariance:
Q0=E[(v0−vˉ0)(v0−vˉ0)T]
Measurement noise covariace:
R0=E[(w0−wˉ0)(w0−w^0)T]
Algorithm 1 Extended Kalman Filter (EKF)
Symbol
Description
Robot Parameters
o1 , o2 , o3
rear, front-right and front-left wheels
m
robot’s mass
I0
robot’s inertia moment
r
wheel radius
L
body radius
Table 2: Notation for the model equations of the three-wheel robot.
Figure 1: Robot coordinate frame {xr,xr} fixed to the robot’s body (local coordiantes) and the traction forces f1 , f2 and f3 of the wheels.
Figure 2: World coordinate frame {xw,yw} fixed to the court (global coordinates) and two teams of RoboCup F-180 robots.
Figure 3: Forces acting on the robot and velocity components (see Table 2 for notation details).
Figure 4: PUC’s RoboCup F-180 system architecture.
Figure 5: Six different reference trajectories employed in the simulations.
Figure 6: Examples of the measured noisy trajectory corresponding to trajectory in the first row, second column of fig. 5 for different noise realizations.
RMSE w/IF
RMSE wo/IF
Tc/Tcmin
Tc/Tcmin
Filter
Position [ m ]
Heading [ rad ]
Position [ m ]
Heading [ rad ]
w/IF
wo/IF
EKF
0.0048 b
0.2326
0.0229 b
0.2674
1.000
1.000
DD1
0.0434
0.1386
0.0491 c
0.1951
3.566
3.729
DD2
0.0342
0.1363
0.0491
0.1947
3.566
3.729
UKF
0.0379
0.0398 c
0.1101
0.1399 c
3.758
3.971
CDKF
0.0105 c
0.0518
0.1100
0.1398 b
3.727
3.960
Table 3: Results for the 1-frame ahead prediction.
RMSE w/IF
RMSE wo/IF
Tc/Tcmin
Tc/Tcmin
Filter
Position [ m ]
Heading [ rad ]
Position [ m ]
Heading [ rad ]
w/IF
wo/IF
EKF
0.0234 b
0.2078
0.0478 b
0.2510
1.000
1.000
DD1
0.0548
0.1504
0.1232
0.1351
2.499
2.566
DD2
0.0658
0.1535
0.1232
0.1360 b
1.749
2.751
UKF
0.1187
0.0541
0.0617 c
0.2108
3.790
3.965
CDKF
0.0561
0.0325 a
0.0617
0.2115
3.594
3.756
Table 4: Results for the 4-frame ahead prediction.
RMSE w/IF
RMSE wo/IF
Tc/Tcmin
Tc/Tcmin
Filter
Position [ m ]
Heading [ rad ]
Position [ m ]
Heading [ rad ]
w/IF
wo/IF
EKF
0.0611 c
0.2138
0.0828 b
0.2577
1.000
1.000
DD1
0.0884
0.1541
0.0928
0.2145
2.220
2.261
DD2
0.0582 b
0.1373
0.0927 c
0.2143
2.210
2.261
UKF
0.0812
0.0784
0.1549
0.1402 c
3.874
4.024
CDKF
0.1208
0.0400 a
0.1549
0.1395 b
3.561
3.696
Table 5: Results for the 8-frame ahead prediction.
Figure 7: Noise-free reference trajectory.
Figure 8: Measured trajectory.
Figure 9: Predicted trajectory 4-frames ahead using the EKF without the IF.
Figure 10: Predicted trajectory 4-frames ahead using the EKF with the IF.
Figure 11: Predicted trajectory 4-frames ahead using the PF.
Figure 12: Trajectory components xw and yw of a real F-180 robot predicted 4-frames ahead using the EKF with the IF.
Robot trajectory tracking develops methods that make robots follow desired paths or motions accurately despite disturbances, uncertainty, and physical constraints.