Running Pure Pursuit

Where This Fits

Pure Pursuit is a Path Follower — it takes the recorded waypoints and the real-time localized pose from the particle filter, and steers the car along the path. In the future, other algorithms like RRT will also fill this role.

Once waypoints are recorded, the pure pursuit node can drive the car autonomously around the track using the particle filter for localization.

How It Works

Pure Pursuit is a geometric path tracking algorithm. On each update:

1. The node reads the car’s current pose from /pf/pose/odom

2. It finds the lookahead point — a point on the path a fixed distance ahead of the car

3. It computes the steering angle to arc toward that lookahead point

4. It publishes drive commands on /drive

The lookahead distance controls the trade-off between tracking accuracy and smoothness. A shorter lookahead follows the path more tightly; a longer lookahead produces smoother but wider turns.

Note

The pure_pursuit package, launch file, config file, and pure_pursuit_node do not come pre-installed. You must build them yourself first — see Lab 6b - Pure Pursuit in the Weber Assignments for step-by-step instructions on creating the launch file, config, and writing the node.

Prerequisites

• Pure Pursuit node built (see Building the Pure Pursuit Node)

• Waypoints recorded (see Recording Waypoints)

• bringup running (Terminal 1)

• ros2 launch particle_filter localize_launch.py running (Terminal 2)

• RViz2 running with the particle filter config:

  rviz2 -d ~/f1tenth_ws/src/f1tenth_system/particle_filter/rviz/pf.rviz
  

• Initial pose set via 2D Pose Estimate

Steps

1️⃣ Launch Pure Pursuit (Terminal 3)

cd ~/f1tenth_ws
source /opt/ros/humble/setup.bash
source install/setup.bash
ros2 launch pure_pursuit pure_pursuit_launch.py

The car will begin following the recorded waypoints and loop the track continuously.

2️⃣ Visualize in RViz2

Add a Path display in RViz2 to see the recorded waypoints overlaid on the map:

• Click Add → select Path

• Set Topic to /pure_pursuit/path

The car’s progress along the path will update in real time.

Key Parameters

Tune pure pursuit performance by editing the config file:

nano ~/f1tenth_ws/src/pure_pursuit/config/pure_pursuit.yaml

Parameter	Default	Description
lookahead_distance	1.5	Distance ahead on the path to steer toward (meters) — increase for smoother driving at speed
speed	1.0	Forward drive speed (m/s)
waypoint_file	waypoints.csv	Path to the recorded waypoints CSV

Troubleshooting

Problem	Solution
Car immediately stops or spins	Initial pose not set — set 2D Pose Estimate in RViz2 and re-launch
Car cuts corners aggressively	Decrease lookahead_distance
Car oscillates side to side	Increase lookahead_distance; reduce speed
Car drifts off path over time	Particle filter may have diverged — re-set initial pose in RViz2
No waypoints file found	Re-run waypoint recording; confirm path in pure_pursuit.yaml