
When do i need to use "differential" or "relative" in robot_localization node settings in ROS2?

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For each of the sensor messages defined above that contain pose information, users can specify whether the pose variables should be integrated differentially. If a given value is set to true, then for a measurement at time t from the sensor in question, we first subtract the measurement at time t−1

, and convert the resulting value to a velocity. This setting is especially useful if your robot has two sources of absolute pose information, e.g., NAME_1 measurements from odometry and an IMU. In that case, if the variances on the input sources are not configured correctly, these measurements may get out of sync with one another and cause oscillations in the filter, but by integrating one or both of them differentially, we avoid this scenario.

Users should take care when using this parameter for orientation data, as the conversion to velocity means that the covariance for orientation state variables will grow without bound (unless another source of absolute orientation data is being fused). If you simply want all of your pose variables to start at 0, then please use the _relative parameter.
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