The waypoint_updater node is in charge of:
- defining a list of waypoints the car will follow
- setting the proper velocity for them.
The node listens for the /base_waypoints, /current_pose and /traffic_waypoint topics and publishes the new car trajectory
on the /final_waypoints topic.
The node publishes a new trajecotry containing 50 waypoints at a rate of 50 Hz and, at each iteration,
it checks first if a new red light is ahead of the car. If it is actually the case
then the waypoint_updater plans a slow down until a full stop before the red light.
The knowledge of the presence of the red light comes from the tl detector node that
publishes on the /traffic_waypoint topic the id of the waypoint of the red light.
Whenever a message is received from the /traffic_waypoint, the traffic_cb callback gets called and the id of the waypoint
of the red light is saved.