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Plot a Track

Basic Knowledge Requirements

Before diving into this code, here's a quick heads-up on what you'll need to be familiar with:

  1. Python Programming: It's important to have a basic grasp of Python, including plotting / visualization with the matplotlib library.
  2. Record a Track: Follow the example to record the track you will plot in this example and cover the required knowledge for that example to understand Tracks, Waypoints, & Poses.
  3. Transfer Data: Know how to transfer data from your robot to your local PC by following the data transfer section of the Recorder App Guide.

The Track Plotter Example operates as a standalone Python script, in which a Track proto message is plotted using the matplotlib library. This script takes in a pre-recorded track and plots the track.

To successfully run this example, you must use your local PC, as the example won't work if executed directly from a brain (because of the popup window).

1. Install the farm-ng Brain ADK package​

2. Install the example's dependencies​

tip

It is recommended to also install these dependencies and run the example in the brain ADK virtual environment.

Setup​

Recommended

Create a virtual environment

python3 -m venv venv
source venv/bin/activate

Install​

cd py/examples/track_plotter
pip install -r requirements.txt

3. Execute the Python script​

python main.py --track <path-to-your-track>
# Replace <path-to-your-track> to the actual file path to your track
reminder

There's an example to teach you how to record your own track here.

You should now see a matplotlib popup with a plot of your Track.

full_track

If you zoom in on the track, you will see that each waypoint is plotted as an arrow indicating the heading of the waypoint pose.

zoomer_track

4. Code Highlights​

The unpack_track function is what interacts with the Track proto to extract x & y coordinates and heading of each waypoint. This is done by converting each waypoint Pose proto to the Pose3F64 C++ class that is exposed through Pybind. We then extract the required values from this class.

def unpack_track(track: Track) -> tuple[list[float], list[float], list[float]]:
    """Unpack a track from a Track proto message into lists of x, y, and heading values.

    Args:
        track: (Track) The Track proto message to unpack.
    Returns:
        x_values: (list[float]) The x values of the track.
        y_values: (list[float]) The y values of the track.
        headings: (list[float]) The heading values of the track.
    """
    x_values: list[float] = []
    y_values: list[float] = []
    headings: list[float] = []

    waypoint: Pose
    for waypoint in track.waypoints:
        goal: Pose3F64 = Pose3F64.from_proto(waypoint)

        x_values.append(goal.translation[0])
        y_values.append(goal.translation[1])
        headings.append(goal.rotation.log()[-1])

    return x_values, y_values, headings

Congrats you are done!