Pure Pursuit Paths

Pure pursuit follows a pre-drawn path by continuously steering toward a "lookahead point" — the spot where a circle around the robot intersects the path. The result is smooth, fast, multi-point motion that a chain of moveToPoint calls can't match.

Drawing a path

Use path.jerryio:

1. Set the format to LemLib Odom Code Gen v0.4 (Odyssey reads the same format: x, y, speed lines ending with endData).
2. Draw your path on the field image.
3. Adjust the speed profile (the generator bakes deceleration into the waypoint speeds).
4. Download the .txt file.

Running a path from the SD card

Copy the file to a micro SD card (FAT32), insert it into the brain, and:

void autonomous() {
    chassis.setPose(/* match the path's starting point! */);

    //             file          lookahead  timeout
    chassis.follow("skills.txt", 12,        15000);
}

To run a path backwards (robot drives in reverse along it):

chassis.follow("retreat.txt", 12, 5000, false);

Paths in code

No SD card? Define waypoints directly — each is (x, y, speed) with speed in motor power (-127 to 127):

std::vector<odyssey::Waypoint> path = {
    {0, 0, 80},
    {0, 24, 100},
    {12, 36, 100},
    {24, 40, 60},
    {36, 40, 40}, // slow into the final point
};
chassis.follow(path, 12, 8000);

Space waypoints a few inches apart — pure pursuit interpolates between them, but speed lookup uses the nearest point.

Choosing the lookahead distance

The lookahead is the radius of the circle used to pick the steering target, in inches:

• Smaller (6-10) — hugs the path tightly, but can oscillate or feel jerky.
• Larger (15-20) — smooth and stable, but cuts corners.
• Start at 12 and adjust per path. Fast, gentle paths tolerate large lookaheads; tight maneuvers need small ones.

Pure pursuit does not stop precisely

The follower ends when the robot reaches the neighborhood of the final waypoint, while still moving at the path's final speed. End your paths at low speed, and follow with a moveToPoint/moveToPose if you need an exact final position.

Mid-path actions

follow is async like every other motion, so the waitUntil pattern works on distance traveled along the path:

chassis.follow("score.txt", 12, 10000);
chassis.waitUntil(30); // 30 inches into the path
intake.move(127);
chassis.waitUntilDone();