Localization covariance grows unexpectedly

1. Symptoms

• The pose covariance keeps increasing over minutes.
• The robot slows or stops because localisation uncertainty is too high.
• Absolute sensors appear to be active but have no effect.

2. Possible causes

• No absolute measurement source is fused (GNSS, LiDAR pose, markers).
• Corrections are rejected by tight gates.
• Measurement covariances are too large.
• Time stamps too old or future, so measurements are dropped.
• Process noise Q too large.
• A sensor timed out.

3. Measurements to collect

• Covariance over time next to the measurement arrival times.
• Counts of accepted and rejected measurements.
• The sensor timeout events.

4. Diagnostic commands

Commands are not executed by the site’s automated tests (they need a ROS 2 Jazzy installation or the robot).

ros2 topic echo /odometry/filtered --field pose.covariance
ros2 topic hz /odometry/filtered
ros2 topic echo /diagnostics

5. Step-by-step investigation

1. Check which sensors are fused and whether any provides absolute information.
2. Check rejections and thresholds.
3. Check measurement covariances and time stamps.
4. Check Q, including dynamic process noise.
5. Check timeouts.

6. Corrective actions

• Add an absolute source or place landmarks.
• Loosen gates or fix covariances.
• Fix time stamps.
• Tune Q (dynamic process noise stops growth at rest).

7. Validation after the fix

• Covariance stays bounded over a full mission with the absolute sources active.

References

• robot_localization documentation (ros2 branch): state_estimation_nodes.rst and params/ekf.yaml, read 2026-11-06.