[navigation] Creating usage.

Author: Murilo Marinho

docs/source/index.rst

@@ -232,6 +232,7 @@ If you enjoyed this tutorial, please
 
    navigation/index
    navigation/installation
+   navigation/usage
 
 
 Disclaimers

docs/source/navigation/index.rst

@@ -22,7 +22,7 @@ so far in :program:`ROS2` will allow us to understand and interact with ``nav2``
 Nonetheless, there are sizable tutorials dedicated exclusively to navigation. This will not be the case here. The
 focus will be on linking the concepts learned so far and showcasing how they can be combined to interact with existing
 packages from the community. Conceptually, interacting with existing packages should be easy. However, going beyond
-using existing examples will require, possibly, all the knowledge acquired in previous sections. 
+using existing examples will require, possibly, all the knowledge acquired in previous sections.
 
 For illustrative purposes, we will also use the ``slam_toolbox``, meant for simultaneous localisation and mapping (SLAM).
 Whenever a concept from SLAM coincides with a navigation topic, this will be highlighted. However, going into detail

docs/source/navigation/installation.rst

@@ -11,12 +11,14 @@ Installation
 
     Official documentation: https://docs.nav2.org/getting_started/index.html
 
+We will install ``nav2``, a few example packages, and the ``slam-toolbox`` with the following command.
+
 .. rli:: https://raw.githubusercontent.com/UoMMScRobotics/SFR_Gazebo/refs/heads/main/install_nav2.sh
    :language: bash
    :lines: 5-14
 
 The package ``ros-jazzy-navigation2`` contains most of ``nav2``. However, we have to install ``ros-jazzy-nav2-bringup``
-separately owing to "recursive dependencies". See below.
+separately owing to "recursive dependencies". See below all the packages that are installed with ``ros-jazzy-navigation2``.
 
 .. dropdown:: Contents of ``ros-jazzy-navigation2``
 
@@ -25,14 +27,15 @@ separately owing to "recursive dependencies". See below.
        :lines: 15-48
 
 The last package related to ``nav2``, ``ros-jazzy-nav2-minimal-tb*`` has a wildcard that will expand, currently,
-to install the following packages.
+to install the following packages. These are optional packages that will give us some infrastructure to work on the
+tutorial.
 
     - ros-jazzy-nav2-minimal-tb3-sim - Nav2 Minimum TurtleBot3 Simulation
     - ros-jazzy-nav2-minimal-tb4-description - Nav2's minimum Turtlebot4 Description package
     - ros-jazzy-nav2-minimal-tb4-sim - Nav2 Minimum TurtleBot4 Simulation
 
 For illustrative purposes, we also add ``ros-jazzy-slam-toolbox``. Please note that navigation is complementary to
-localisation and mapping, but both can be done in isolation too.
+localisation and mapping. Both can be done in isolation too.
 
 .. admonition:: References
 

docs/source/navigation/usage.rst

@@ -0,0 +1,48 @@
+Using ``nav2``
+==============
+
+.. versionadded:: Jazzy
+
+   This section.
+
+.. include:: ../the_topic_is_under_heavy_construction.rst
+
+There is a plethora of online examples of ``nav2``, with varying levels of detail and quality. My approach will top-down,
+where we will see how illustrative examples and then walk through their contents.
+
+Navigation on a known map
++++++++++++++++++++++++++
+
+.. seealso::
+
+    Official documentation: https://docs.nav2.org/tutorials/docs/navigation2_on_real_turtlebot3.html
+
+In this example, our interest is looking at how navigation can be done with built-in tools, using a known *map*. A
+map will have many definitions and the literature about it is extensive. For now, we can think of the map as something
+usual. It points out where things are, where passable (such as roads) regions are, and possibly hazards and other
+relevant objects.
+
+In this example, a `TurtleBot3 <https://www.turtlebot.com/turtlebot3/>`_ will be used. As part of ``nav2_bringup``, there
+is a rather complete example that we can utilize, namely :file:`tb3_simulation_launch.py`.
+
+.. warning::
+
+    The ``sigterm_timeout`` flag is particularly important. Given that some devices we use might not be powerful enough
+    for all processes to finish cleanly within 5 or 10 seconds, we should add this to prevent a ``SIGTERM`` from
+    being sent to the nodes. If nodes are not terminated correctly they can leave connections open, linger indefinitely,
+    and cause extremely difficult-to-debug situations. This can also be dangerous when real robots are used.
+
+.. code-block:: console
+
+    ros2 launch nav2_bringup tb3_simulation_launch.py use_sim_time:=True headless:=False sigterm_timeout:=120
+
+Navigation with SLAM
+++++++++++++++++++++
+
+.. seealso::
+
+    Official documentation: https://docs.nav2.org/tutorials/docs/navigation2_with_slam.html#navigation2-with-slam
+
+.. code-block:: console
+
+    ros2 launch nav2_bringup tb3_simulation_launch.py slam:=True sigterm_timeout:=120