The code for this section is located in navigation_bot_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. Note also that we use ROS2 Galactic now.
We want to make our robot move along the specific path. There can be a better path from the navigation point of view, but we can easily come up with real life applications that would require following an exact path instead. For example, we might want our robotic vacuum cleaner to move from bathroom to kitchem. If we ask navigator to come up with a route, it is going to be a line: a shortest path. But if we want our robot to clean the floor, we have to force it to go in some kind of a zigzag path instead. Same for a robot on a farm: if we want the robot to make photos of each plant in our garden, we have to give it exact locations of the plants and also the path to get there, as we do not want it to go across strawberries.