Lab 6: SLAM and Pure Pursuit

I. Learning Goals

• SLAM
• Localization with Particle Filter
• Pure Pursuit Algorithm

II. Running slam_toolbox on the car

Follow the instructions in class to run slam_toolbox to make a map of Levine second floor. Save the map as levine_2nd.pgm and levine_2nd.yaml.

III. Localization with Particle Filter

Follow the instructions in class to run particle_filter on the car using the new map you've made on Levine second floor.

IV. Pure Pursuit Implementation

We have provided a skeleton for the pure pursuit node. As per usual, test your algorithm first in the simulator before you test it on the car. When you're testing in the simulator, use the groud truth pose provided by the sim as the localization. When you move to the car, use particle filter to provide localization.

As shown in the lecture, the curvature of the arc to track can be calculated as:

$$\gamma=\frac{2|y|}{L^2}$$

V. Logging Waypoints

There are several methods you can use to create waypoints for a specific map.

1. Recording a trajectory of joystick driven path. You can write a node that subscribe to the pose provided by the particle filter localization, and save the waypoints to a csv file. A similar script is provided here. Note that this script is in ROS 1 and you'll have to write a ROS 2 node.

2. Find key points in the map (e.g. in the Levine loop, the four corner centers of the loop) and create a interpolated spline that goes through all four corners. You can use functions such as scipy.interpolate.splprep and scipy.interpolate.splev. You can find more documentaion on these here and here.

Usually, you'll just save the waypoints as .csv files with columns such as [x, y, theta, velocity, arc_length, curvature]. With pure pursuit, the bare minimum is [x, y] positions of the waypoints. Another trick is that you can also smooth the waypoints if you decided to record it with the car. You can subsample the points you gathered and re-interpolate them with the scipy functions mentioned above to find better waypoints.

VI. Visualizing Waypoints

To visualize the list of waypoints you have, and to visualize the current waypoint you're picking, you'll need to use the visualization_msgs messages and RViz. You can find some information here.

VII. Deliverables

• Deliverable 1: Submit the map files (levine_2nd.pgm and levine_2nd.yaml) that you've made using slam_toolbox.
• Deliverable 2: Commit your pure pursuit package to GitHub. Your commited code should run smoothly in simulation.
• Deliverable 3: Submit a link to a video on YouTube showing the real car following waypoints in Levine hallway. Show a screen recording of rviz.

VIII: Grading Rubric

• Compilation: 10 Points
• Running slam_toolbox and producing a map: 30 Points
• Running particle_filter: 20 Points
• Implementing pure pursuit: 30 Points
• Video: 10 Points