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Track Follower Service Overview

The Track Follower is the autonomy hub of the Amiga. It takes in user commands and turns them into actions the robot can perform.

The main goal of the Track Follower is to act as a bridge between what you want the Amiga to do and how the robot actually does it. It hides the complicated details, letting users focus on their main tasks without needing to know the complex workings underneath.

In short, the Track Follower does the heavy lifting, allowing users to easily command the Amiga without deep technical knowledge.

Subscriptions​

The track_follower is a client of the following services:

remember

The State estimation filter service is also client of the following services:

For this reason, all of the above-mentioned services must be up and running for the track_follower to work.

Data Streams

  • /state: The TrackFollowerState is a combination of information from the various tasks performed by the Track Follower. It cannot be defined by a single protobuf definition, but instead, a combination of them. Check out the protobuf definitions for the Track Follower service for more details at track.proto

API​

These are the commands you can use to interact with the track follower service with an EventClient of the track follower service.

  • /set_track: Provide a specific Track (series of waypoints) for the Amiga to follow.
  • /start: Instruct the Amiga to start following the recently set `Track``.
  • /pause: Pause following the track, but maintain knowledge of the progress along the Track.
  • /resume: Continue following the track from where a /pause was called.
  • /cancel: Instruct the Amiga to halt all movements immediately and clear the set Track.
  • /get_track: Return the Track that was set with /set_track
  • /get_state: Return a single instance of the TrackFollowerState streamed on the /state topic.
  • /go_to_goal: Send a single Pose as a waypoint for the Track Follower to drive to.
    • Must be within a few meters and 180 degrees of the robot's current pose and orientation.

Requirements​

There are a few requirements on the /state output of the state estimation filter (see FilterState) for the track follower service to consider the results valid and allow for following a track. These include:

  • GPS service is connected to an RTK base station
  • State estimation is receiving all required sensor data
  • State estimation results have converged
    • Requires a few seconds of driving around after starting the filter service

The Track Follower in practice​

Before the track follower can drive the Amiga autonomously, users must set a predefined track for the robot to follow using the /set_track API.

Once a track is set, the next step is to command the track follower to make the robot follow it. This is done using the /start request. The track follower will then navigate the robot through each waypoint in the sequence, ensuring it follows the predefined path.

Remember

It's crucial first to set the track before asking the robot to follow it. The track follower expects the sequence of waypoints in the order they should be traversed. Without a set track, the track follower wouldn't know where to direct the robot.

Features​

The track follower offers a level of flexibility and intelligence that goes beyond simply following a predefined path. Once a track is set, the robot can also traverse it in a few unique ways:

  1. Reversing the Track: After the Amiga has learned a track, it's not restricted to following it in just the direction it was taught. The end point of the learned track can seamlessly become the starting point, provided the robot is oriented towards its recorded initial position. This allows the robot to navigate environments bidirectionally, offering greater autonomy and adaptability in dynamic settings.

  2. Initiating from Intermediate Points: You don't always have to start the robot from the beginning of a track. The track follower is smart enough to allow track following from any intermediate point within the path. This is especially useful if the robot needs to start its journey from a point that's not the traditional beginning or end.

Requirements for Following a Track​

For the track follower to begin guiding the robot along a track, certain conditions must be met to ensure accurate and safe navigation:

Proximity to the Track: The robot must be situated closely to an existing point on the track. This ensures it's close enough to align itself correctly and follow the track.

Orientation or Heading: The robot's heading needs to align closely with the heading of the nearest point on the track. Specifically, it should be within 30 degrees of the track point's heading. This condition ensures the robot is oriented correctly and can safely navigate along the desired path without sudden, unexpected maneuvers.

Tracks​

A track is essentially a sequence of waypoints, guiding the robot from its starting point, through various intermediary points, to its destination. Each waypoint in this track provides specific spatial information about where the robot should be and how it should be oriented at that point.

Define a Track​

A track is represented as a JSON file, where each waypoint is defined by a pose. A pose captures the robot's position and orientation in the world. Here's an example of what a single pose looks like:

{
  "pose": {
    "aFromB": {
      "rotation": {
        "unitQuaternion": {
          "imag": {
            "z": -0.9932486190247055
          },
          "real": 0.11600508956729176
        }
      },
      "translation": {
        "x": 2674.593868581748,
        "y": 4297.325262829638
      }
    },
    "frameA": "world",
    "frameB": "robot",
    "tangentOfBInA": {
      "linearVelocity": {
        "x": 0.4467579546503179
      },
      "angularVelocity": {
        "z": 0.00475509022854358
      }
    }
  },
  "heading": -2.909058930621276
},

Examples​

Now that you have a good understanding of how the track follower works, try some of the track follower examples:

Warning

The track follower examples will cause the Amiga to drive when the dashboard is in auto mode. Make sure the area is clear before running examples.

You can also run the examples when the Amiga dashboard is not in AUTO READY or AUTO ACTIVE and see the commands being sent with the red needle on the auto page without the Amiga actually moving.