What you will need

• A working Duckiebot: Duckiebot Subsystems

• A functional dts installation: Duckietown Shell (dts)

• A camera calibration pattern, such as one provided in a Duckiebox.

What you will get

• A Duckiebot whose extrinsics camera calibration has been completed.

Extrinsic camera calibration procedure

This camera calibration procedure outputs the relative pose between the camera and Duckiebot frame.

For optimal performance, repeat this procedure if you ship the Duckiebot or otherwise touch the camera holder.

The Extrinsics Calibrator

The easiest way to perform the extrinsic camera calibration procedure for your Duckiebot is by using the Extrinsics Calibrator.

Fig. 68 The Extrinsics Calibrator.

Attention

Before proceeding, make sure that you can ping your Duckiebot using the following command, where DUCKIEBOT_NAME is the name of your Duckiebot:

ping DUCKIEBOT_NAME.local

Ubuntu

To open the Extrinsics Calibrator, run the following command, where the --browser flag opens the WebGL (browser) version:

dts duckiebot calibrate_extrinsics DUCKIEBOT_NAME [--browser]

Duckietown Workspace

To open the Extrinsics Calibrator, if dts is installed on the host machine, run the following command from a terminal inside the Duckietown Workspace or on the host machine:

dts duckiebot calibrate_extrinsics DUCKIEBOT_NAME

Note

This command will be delegated to the host machine if it is run inside the Duckietown Workspace.

Note

The first time a Duckietown Viewer app is run, a pop-up window may appear and request permission. Enter your password and select “(Always) Allow” to continue.

Alternatively, to open the WebGL (browser) version of the Extrinsics Calibrator, open a terminal inside the Duckietown Workspace or on the host machine (if dts is installed on the host machine) and run:

dts duckiebot calibrate_extrinsics DUCKIEBOT_NAME --browser

Note the keys in the table below.

Key	Function
X	Increase the Frame Rate
Z	Decrease the Frame Rate
Space	Calibrate the camera
F	Toggle the Project switch
E	Toggle the Check error switch
R	Refresh the window
T	Open the Debug Console

Extrinsic calibration procedure

To perform the extrinsic calibration procedure:

1. (Optional) Click the Check error switch to enforce a pose error bound for your Duckiebot’s camera based on its known intrinsic parameters (a trapezoid in the image under Camera View should appear).

2. Position your Duckiebot on the calibration board such that it faces the checkerboard pattern, your Duckiebot’s axle is parallel to and directly above the large y-axis of the calibration board, and the axis that is perpendicular to and midway between your Duckiebot’s axle is directly above the large x-axis of the calibration board (if the Check error switch is set to on, the trapezoid in the image under Camera View should turn from black to blue).

3. Click the Calibrate button.

4. Wait for the spinner to disappear.

5. (Optional) Click the Project switch to see a top-down view of what your Duckiebot sees under Projection.

Fig. 69 Extrinsic calibration setup: align the Duckiebot with the marks on the calibration pattern, on a white backdrop.

Fig. 70 The Extrinsics Calibrator with the Check error switch set to on.

Fig. 71 The Extrinsics Calibrator with the Project switch set to on.

To confirm that a new extrinsic calibration file has been created on your Duckiebot, run the following command and inspect the contents of the Camera Extrinsic panel:

dts duckiebot dashboard DUCKIEBOT_NAME --page robot/calibrations

Fig. 72 The Camera Extrinsic panel on the Robot page of the Dashboard.

Note

Within the Camera Extrinsic panel, under Local, you should see a tick next to Completed, the calibration date next to Calibration date and /data/config/calibrations/camera_extrinsic/DUCKIEBOT_NAME.yaml next to Files.

Troubleshooting

Troubleshooting

SYMPTOM

When I open a calibrator window, I see a gray loading screen instead of images in the center. I know that the camera otherwise works on my Duckiebot.

RESOLUTION

Press the refresh icon on the top right of the calibrator window to restart the image stream.