docs: explain how to select SE from MOLA-LO launch files

docs/mola_state_estimators.rst

@@ -17,6 +17,9 @@ ____________________________________________
 
 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?
@@ -25,28 +28,88 @@ Frames of reference.
 
 |
 
-2. Supported inputs
+2. Selecting the S.E. method in launch files
+------------------------------------------------
+In the context of launching LiDAR odometry (LO) mapping or localization
+as explained :ref:`here <launching_mola_lo>`, note that default configurations
+include ``StateEstimationSimple`` as the method of choice, but it can be 
+changed as follows:
+
+.. dropdown:: MOLA-LO with a custom State Estimation configuration
+   :icon: code-review
+
+   Both, all MOLA-LO GUI applications, and the ROS node, rely on MOLA system :ref:`configuration files <yaml_slam_cfg_file>`
+   to know what MOLA modules to launch and what parameters to pass to them.
+
+   - `Read through those files <https://github.com/MOLAorg/mola_lidar_odometry/tree/develop/mola-cli-launchs>`_
+     to fully understand what is under the hood.
+   - Default parameter files for estimators are provided under `mola_lidar_odometry/state-estimator-params <https://github.com/MOLAorg/mola_lidar_odometry/tree/develop/state-estimator-params>`_.
+
+   So, what follows are just examples that should be considered starting points for user customizations by using custom S.E. parameter files:
+
+   .. tab-set::
+
+      .. tab-item:: Defaults
+         :selected:
+
+         .. code-block:: bash
+
+            # 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 $(ros2 pkg prefix mola_lidar_odometry)/share/mola_lidar_odometry/pipelines/lidar3d-default.yaml \
+              --input-kitti-seq 04
+
+      .. tab-item:: Custom state estimator configuration
+
+         .. code-block:: bash
+
+            # Launch LO-GUI on the KITTI dataset, using the smoother state estimator:
+            MOLA_STATE_ESTIMATOR="mola::state_estimation_smoother::StateEstimationSmoother" \
+            MOLA_STATE_ESTIMATOR_YAML="$(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. Supported inputs
 ---------------------------------
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 |
 
-3. C++ generic API
+4. C++ generic API
 ---------------------------------
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 |
 
-4. Implementations
+5. Implementations
 ---------------------------------
 
-4.1. Simple estimator
+5.1. Simple estimator
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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 |
 
-4.2. Factor graph smoother
+5.2. Factor graph smoother
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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