An important info about the structure of this code.
The first part of the code for this section is located both in nav25d_08 part of an archive Note that archive includes some additional folders, like maps and worlds, that are used by all projects and therefore are located outside of them. Also note that currently the ROS2 Galactic is used.
As for the second part: the tutorial is divided in two parts. First part is about the theory, it is complete and free (see below).
The localization code itself however is divided into two fragments. The free fragment is available in
the archive above and it works without any additions. But Kalman part of
that code is moved to a commercial section:
kalman_nav.zip.
Note: This archive should be added to same folder where you have unpacked
archive.
Let me explain how it works and why do you need commercial code if free code works just fine.
A kalman.py file was moved to commercial section and therefore will not be available unless you get it and copy it over to nav25d_07/nav25d_08 folder. The (free) Navigation.py file checks if this file is present and either uses it (in which case you will get a complete Kalman based localization) or not (in which case Kalman filter is replaced with a rather primitive simulation).
As the result, in a Gazebo simulator, all future demos will work even without commercial files. But of course, in a real world your robot will not have localization abilities.
Important note: as I write more sections, the kalman_nav.zip file will get additional context. Once purchased, it gives you 1 year of access, so if (when?), for example, I make the navigation to respect the fact that the world is round, or whatever else related to localization - it will go to this archive and will be available with the same subscription. Unless this project is terminated, of course.