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.