Data collection for rough terrain vehicle-Lidar calibration
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.
- 1.We need an additional camera which is used as a support (external) camera. 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.Stick Aruco markers to the vehicle wheels to auto-detect the wheel center. Click here for Aruco markers. Note: The ArUco markers must match the wheel position. Mismatched markers will not be recognized in the application.
- 3.Place and fix the checkerboard position in the mounted lidar's field of view. A point cloud is extracted from the mounted Lidar sensor.
- 4.Take an image from the external camera having a front-left wheel, rear-left wheel, and checkerboard in its field of view. Note: Using a tripod with the the external camera can reduce motion blur and improve calibration accuracy.
- 5.Move the external camera to a different location and take another image. Repeat the process for at least three iteration. Note: The vehicle, ArUco tags, and checkerboard should all be static during steps 4 and 5.
- 6.Now repeat the entire steps from 3 to 5 by moving the external camera to the right side of the vehicle.
Checkerboard placed in the view of the mounted lidar.
Image taken from external camera with front-left wheel, rear-left wheel and checkerboard in its field of view.
Image taken from external camera with front-right wheel, rear-right wheel and checkerboard in its field of view.
- 1.Try to use aruco markers of higher length. Measure the length of the aurco marker once printed, and configure same value in the tool.
- 2.Try to make sure the aruco marker is as plain as possible. Aluminium Dibond can be used for the same purpose.
- 3.Have the checkerboard tilted to the right, this helps to detect the checkerboard edge points and then make the sparse checkerboard dense.
- 4.Use accurate intrinsic parameters for the external camera as this method mostly depends on the aruco marker detection on the wheels.