Data Collection for Vehicle-Camera Calibration
Checkerboard is the calibration target. A large checkerboard is required because the external camera is usually quite far away. For small vehicles (cars), the minimum checkerboard size is 0.6m^2. For large vehicles (e.g., farm tractors), the minimum checkerboard size is 2.4m^2 because the camera is further away. If you are calibrating a small vehicle, you can print the attached pdf file on a foam board at 1.0m × 0.6m. Most print shops can print this. https://drive.google.com/file/d/1mTR8HTpvROE1Pv0rmXEBVLSxs_yMDnvf/view?usp=sharing
Data collection for vehicle-camera calibration:
- 1.We need one mounted on the car w.r.t which we do the calibration against the vehicle.
- 2.We need to make sure we have the intrinsic parameters for the cameras before we proceed to vehicle-camera calibration. Intrinsics can be obtained from the camera-intrinsic calibration tool as well.
- 3.Have a checkerboard with known horizontal corners and vertical corners. And also the square size.
- 4.Mark the boundaries of the vehicle using the tape, then mark a parallel line to the vehicle based on the orientation of the camera
- 5.Use tape in order to take precise measurements, along with a carpenter scale, to make sure the board is exactly perpendicular to the ground
- 6.Place the board on this parallel line
- 7.Make sure the board is parallel or perpendicular to the car sides, based on the configuration of the camera
- 8.Take measurements of the checkerboards distance from the respective side of the vehicle by measuring the distance of the parallel line the checkerboard is on to the vehicle side it is parallel to and also measures how far the checkerboard is, from the left side of the line
- 9.Take multiple shots of the checkerboard with the checkerboard placed at multiple distances away from the left, along the same parallel line.
- 10.Also, measure the required vehicle config
Example photo 1 of the checkerboard
Example photo 2 of the checkerboard
Required vehicle configuration for a rectangular vehicle
Required vehicle configuration for trapezoid vehicle
Reference Points for Data Collection:
1. Paste the adhesive tape on the ground along the edges of the vehicle based on the camera-facing direction. Assume calibrating the front-facing camera sensor as an example for this collection process. Paste the adhesive tape as shown in figure 5 for the front-facing camera. (See How to paste adhesive tape along vehicle for different camera facing directions?)
Figure 5: Adhesive tape on vehicle edges for the front-facing camera
2. To maintain a fixed distance between the target and the vehicle, paste the adhesive tape parallel to the vehicle with a 1-10m distance between the target and the vehicle as shown in figure 6. It acts as a Reference Line (RL) for the target.
Figure 6: Reference line 1-10m in front of the vehicle
Vehicle Reference Point (VRP): The left intersection point (from the camera perspective) of the adhesive tape pasted along the vehicle's edges, as shown in figure 7.
Intersection Reference Point (IRP): This is the left intersection point of the adhesive tape from the vehicle with the adhesive tape from the reference line, as shown in figure 7.
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Figure 7: Vehicle and intersection reference points on tape
Target Reference Point (TRP): This is the bottom-left edge corner of the target, as shown in figure 8.
Figure 8: Target reference point
4. Measure the distance between VRP and IRP and note it down.
5. Place the calibration target perpendicular to the ground, facing towards the vehicle, as shown in figure 9. The bottom edge of the target aligns with the adhesive tape. If the target is parallel to the ground, ensure the bottom edge of the target aligns with the adhesive tape, which results in the target being away from the vehicle as shown in figure 10.
Figure 10: Calibration target parallel to the ground
6. Measure the distance between IRP and the TRP and note it down.
7. Capture an image from the camera sensor and note down the name of the image file next to the data collected from steps 5 and 6.
8. You can upload 1-10 images for the calibration; we recommend capturing at least three images with the target perpendicular to the ground and at least three images parallel to the ground in different positions on the RL to maximize accuracy.
Figure 9: Calibration target perpendicular to ground
Figure 11: Adhesive tape for front-facing camera
Figure 12: Adhesive tape for rear-facing camera
Figure 13: Adhesive tape for left-facing camera
Figure 14: Adhesive tape for right-facing camera