Data Collection for Lidar-Camera Calibration (Single Target)

Calibration Target

1. Checkerboard of more than two horizontal inner corners and vertical inner corners. You can use the attached pdf. It has seven internal corners horizontally and nine internal corners vertically. https://drive.google.com/file/d/1mTR8HTpvROE1Pv0rmXEBVLSxs_yMDnvf/view?usp=sharing

2. Charucoboard of more than two horizontal and vertical squares. Click here for supported Charuco dictionaries.

Target-based calibration

Data collection

Place the target roughly 3m to 5m from the camera. For the closest target position, the closer should be far enough so that all the board's edges are visible from the camera and lidar. So, it is highly recommended to do this capture inside a building rather than outside. No target position should be occluded in the camera or lidar view.

The same target should be used in all camera and lidar frames.

For example, please take images with a single board at various positions like the following.

The boards and all sensors should be static while collecting the data. To avoid time-synchronization problems, please keep the boards and the sensors stationary for at least 10 seconds while collecting each data pair.

For example, these are the steps to collect one set of calibration data:

1. Orient the camera toward the target. Start recording. Wait for 10 seconds (Don't move/rotate your car/robot/sensors). Stop recording. You must have a recording of images and lidar data for 10 seconds. Extract one image from the camera, and one frame of lidar data captured 5 seconds after the recording has started (e.g., if you start recording at 3:00:00, you stop recording at 3:00:10. We need a frame captured at 3:00:05) and save them.

2. Change the target's location and orientation. Start recording. Wait 10 seconds (Don't move/rotate your car/robot). Stop recording. Again, you must have a recording of images and lidar data for 10 seconds. Extract one image from the camera, and one frame of lidar data captured 5 seconds after the recording starts and save them.

3. Repeat the process for at least 5 data pairs.

Optional Board Position

on-ground: The target is placed on the ground (touching the ground). In such a case, enable the on ground flag in the target configuration. Also, make sure that the lidar data captures the ground points. By doing so, we can optimize the extrinsic parameters using the ground points.

Tilted: A holder holds the target up in the air and tilts right by around 45 degrees. In such a case, enable the Tilted flag in the target configuration. This approach enables deep optimization, and the extrinsic parameters are further optimized using the edge points of the board.