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Notes taken from Udacity class

Nodes

1. traffic light detector

  • subscribed topics:
    • /base_waypoints: repeated list of all waypoints
    • /camera/image_raw: updated images
    • /current_pose: current position of vehicle
  • published topics:
    • /traffic_waypoint:
  • helper topics:
    • /vehicle/traffic_lights: simulator publishes the location and current color state of all traffic lights in the simulator. It can be used for training data collection or as a stub for testing of other components.
  • node files:
    • tl_detector/tl_detector.py: node file
    • tl_detector/light_classification_model/tl_classifier.py: classifier model
    • tl_detector/traffic_light_config: This config file contains information about the camera (such as focal length) and the 3D position of the trafic lights in world coodinates

2. waypoint updater

The purpose of the node is to publish a fixed number of waypoints ahead of the vehicle with the correct target velocities, depending on traffic lights and obstacles.

  • subscribed topics:
    • /base_waypoints: repeated list of all points
    • /obstacle_waypoints: NOT THERE!
    • /traffic_waypoint
    • /current_pose
  • published topics:
    • /final_waypoints: only waypoints ahead up to LOOKAHEAD_WPS.
  • node files:
    • waypoint_updater/waypoint_updater.py

3. twist controller (DBW drive-by-wire)

  • subscribed topics:
    • /current_velocity
    • /twist_cmd
    • /vehicle/dbw_enabled
  • published topics:
    • /vehicle/throttle_cmd
    • /vehicle/steering_cmd
    • /vehicle/brake_cmd
  • node files:
    • twist_controller/dbw_node.py

Message types

Intuition behind sevearl types

  • a lane is a collection of waypoints with header
  • a waypoint consists of pose and twist
  • pose has a xyz position and xyzw orientation
  • twist has a linear (xyz) speed and angular (xyz) speed

In details

  • /base_waypoints: styx_msgs/Lane
  • /camera/image_raw: sensor_msgs/Image
  • /current_pose: geometry_msgs/PoseStamped
  • /final_waypoints: styx_msgs/Lane
  • /traffic_waypoint: std_msgs/Int32 (indx of all /base_waypoints)
  • /current_velocity: geometry_msgs/TwistStamped
  • /twist_cmd: geometry_msgs/TwistStamped
  • /vehicle/dbw_enabled: std_msgs/Bool
  • /vehicle/throttle_cmd: dbw_mkz_msgs/ThrottleCmd
  • /vehicle/steering_cmd: dbw_mkz_msgs/SteeringCmd
  • /vehicle/brake_cmd: dbw_mkz_msgs/BrakeCmd

Team Work