ROS

The Robot Operating System (ROS) is a flexible framework for writing robot software.
ROS is a framework on top of the O.S. that allows it to abstract the hardware from the software.
It is a collection of tools, libraries, and conventions that aim to simplify the task of creating complex and robust robot behavior across a wide variety of robotic platforms.
ROS was built from the ground up to encourage collaborative robotics software development.

Code Structure of ROS

ROS has following nodes to divide task:

Traffic Detection Node

This node takes in data from the /image_color, /current_pose, and /base_waypoints topics and publishes the locations to stop for red traffic lights to the /traffic_waypoint topic.
The /current_pose topic provides the vehicle's current position, and /base_waypoints provides a complete list of waypoints the car will be following.

Waypoint Updater Node

The purpose of this node is to update the target velocity property of each waypoint based on traffic light and obstacle detection data.
This node will subscribe to the /base_waypoints, /current_pose, /obstacle_waypoint, and /traffic_waypoint topics, and publish a list of waypoints ahead of the car with target velocities to the /final_waypoints topic.

Control of the Vehicle Node

This package contains the files that are responsible for control of the vehicle: the node dbw_node.py and the file twist_controller.py, along with a pid and lowpass filter.
The dbw_node subscribes to the /current_velocity topic along with the /twist_cmd topic to receive target linear and angular velocities.
Along with that, this node will subscribe to /vehicle/dbw_enabled, which indicates if the car is under dbw or driver control.
This node will publish throttle, brake, and steering commands to the /vehicle/throttle_cmd, /vehicle/brake_cmd, and /vehicle/steering_cmd topics.

Server for Communication Node

Node contains a server for communicating with the simulator, and a bridge to translate and publish simulator messages to ROS topics.

Messages Node

This node which includes definitions of the custom ROS message types used in the project.

Waypoint Loader node

Waypoint Follower Node

This node subscribes to /final_waypoints and publishes target vehicle linear and angular velocities in the form of twist commands to the /twist_cmd topic.