Data Collection for Rough Terrain Vehicle-Camera Calibration

Calibration Target:

Checkerboard is the calibration target. For small vehicles, the minimum checkerboard size is 0.6m^2. For large cars, the minimum checkerboard size is 2.4m^2. If calibrating a small car, you can print the below pdf file on a foam board at 1.0m x 0.6m. Most print shops can print this. https://drive.google.com/file/d/1mTR8HTpvROE1Pv0rmXEBVLSxs_yMDnvf?usp=sharing

For car wheels, use the Aruco markers. Click here for Aruco markers. Note that the ArUco markers should be as large and flat as possible with a white border. The white border is necessary for tag detection.

Data collection for vehicle-camera calibration:

1. We need two cameras,

   1. A mounted camera on the car with respect to which calibration is done against the vehicle.

   2. An external camera to take images from both left and right sides of the vehicle. Note: The external camera should have a fixed focal length. Changing focal length / auto-focus will change the camera intrinsic parameters. A DSLR with manual fixed focal length can make a good external camera. Modern cell phone cameras all have auto-focus so should not be used as an external camera.

2. Intrinsic parameters for both mounted and external cameras before proceeding to vehicle-camera calibration. Intrinsics can be obtained from the Camera Intrinsic calibration as well.

3. Have a checkerboard with known horizontal corners, vertical corners, and square size.

4. Stick Aruco markers to the vehicle wheels to auto-detect the wheel center. Click here for Aruco markers. Note that the ArUco markers should be as large and flat as possible with a white border. Note: The ArUco markers must match the wheel position. Mismatched markers will not be recognized in the application.

Front Left:

Front Right:

Rear Left:

Rear Right:

Setup and Data collection from the Left-side of the vehicle

1. Place and fix the checkerboard position in the mounted camera's field of view.

2. Take an image from the mounted camera.

3. Take an image from the external camera having a front-left wheel, rear-left wheel, and checkerboard in its field of view. Move the external camera to a different location and take another image. Repeat the process for at least three iterations. Note: Using a tripod with the the external camera can reduce motion blur and improve calibration accuracy.

Note: The vehicle, ArUco tags, and checkerboard should all be static during these 3 steps.

Checkerboard placed in the mounted camera's field of view

Image taken from external camera with front-left wheel, rear-left wheel and checkerboard in its field of view.

Setup and Data collection from the Right-side of the vehicle

1. Place and fix the checkerboard position in the mounted camera's field of view.

2. Take an image from the mounted camera.

3. Take an image from the external camera having a front-right wheel, rear-right wheel, and checkerboard in its field of view. Move the external camera to a different location and take another image. Repeat the process for at least three iterations.

Note: The vehicle, ArUco tags, and checkerboard should all be static during these 3 steps.

Checkerboard placed in the mounted camera's field of view

Image taken from external camera with front-right wheel, rear-right wheel and checkerboard in its field of view.