State estimators


1. Theory

State Estimation (SE) comprises finding the vehicle kinematic state(s) that best explain the imperfect, noisy sensor readings.

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What? Why? How?

Frames of reference.


2. Selecting the S.E. method in launch files

In the context of launching LiDAR odometry (LO) mapping or localization as explained here, note that default configurations include StateEstimationSimple as the method of choice, but it can be changed as follows:

MOLA-LO with a custom State Estimation configuration

Both, all MOLA-LO GUI applications, and the ROS node, rely on MOLA system configuration files to know what MOLA modules to launch and what parameters to pass to them.

So, what follows are just examples that should be considered starting points for user customizations by using custom S.E. parameter files:

# Launch LO-GUI on the KITTI dataset, using the default state estimator:
mola-lo-gui-kitti 04

# Launch MOLA-LO (CLI version) on KITTI, using default state estimator:
mola-lidar-odometry-cli \
  -c $(ros2 pkg prefix mola_lidar_odometry)/share/mola_lidar_odometry/pipelines/lidar3d-default.yaml \
  --input-kitti-seq 04

# Launch LO-GUI on the KITTI dataset, using the smoother state estimator:
MOLA_STATE_ESTIMATOR="mola::state_estimation_smoother::StateEstimationSmoother" \
MOLA_STATE_ESTIMATOR_YAML="$(ros2 pkg prefix mola_lidar_odometry)/share/mola_lidar_odometry/state-estimator-params/state-estimation-smoother.yaml" \
  mola-lo-gui-kitti 04

# Launch MOLA-LO (CLI version) on KITTI, using the smoother state estimator:
mola-lidar-odometry-cli \
  -c $(ros2 pkg prefix mola_lidar_odometry)/share/mola_lidar_odometry/pipelines/lidar3d-default.yaml \
  --state-estimator "mola::state_estimation_smoother::StateEstimationSmoother" \
  --load-plugins libmola_state_estimation_smoother.so \
  --input-kitti-seq 04

# idem, using non-default state-estimation parameters:
mola-lidar-odometry-cli \
  -c $(ros2 pkg prefix mola_lidar_odometry)/share/mola_lidar_odometry/pipelines/lidar3d-default.yaml \
  --state-estimator "mola::state_estimation_smoother::StateEstimationSmoother" \
  --state-estimator-param-file $(ros2 pkg prefix mola_lidar_odometry)/share/mola_lidar_odometry/state-estimator-params/state-estimation-smoother.yaml \
  --load-plugins libmola_state_estimation_smoother.so \
  --input-kitti-seq 04

3. API and supported inputs

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imgs/mola_state_estimation_api_overview.webp

4. Implementations

4.1. Simple estimator

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4.2. Factor graph smoother

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