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Data Collection for vehicle radar calibration
A trihedral corner reflector is used as the calibration target.
The trihedral corner reflector is made by combining three triangles at an angle of 90 degrees. It has a high radar cross-section, and it is easily distinguishable from other objects. The side length an can be chosen of any length, higher values will have higher radar cross-sections. For internal testing purposes, we used the trihedral corner reflectors made of aluminium.
source: Internet
Place the target at multiple places in the field of view of the radar. Record the radar x, y and z coordinates from the radar sensor with high RCS, as the target has a high radar cross-section. Also, collect the configuration of the target w.r.to vehicle for each position.
Make sure to vary the height of the radar position from the ground and collect data from different positions.
Also, there is documentation within the application, which explains the exact steps that are required for the data collection and the values to be configured. Click on Learn how for more information.
What are the things required to collect data?
Calibration Target: Trihedral Corner Reflector.
Figure 1: Trihedral Corner Reflector
- A measuring tape or a ruler to calculate the distance between the calibration target and the vehicle.
- Colored adhesive tape to paste on the ground along the edges of the vehicle's edges.
How to measure the vehicle dimensions?
1. Wheelbase: Calculate the distance between the center of the left/right front wheel and the left/right center of the rear wheel, as shown in Figure 2.
2. Track: Calculate the distance between the left edge of the front/rear wheel and the right edge of the front/rear wheel as shown in Figure 3.
3. Overhang: Calculate the distance between the center of the front/rear wheel to the front/rear bumper of the vehicle, as shown in Figure 4.
Figure 2: Measuring wheelbase
Figure 3: Measuring track
Figure 4: Measuring overhang
How to collect the data for calibration?
1. Paste the adhesive tape on the ground along the vehicle's edges based on the radar direction. Assume calibrating the front-facing radar 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 sensor facing directions?)
2. Paste the adhesive tape parallel to the vehicle, 1-5m away from the vehicle’s edge as shown in Figure 6. It acts as Reference Line (RL) for the target.
3. The below reference points are essential to the data collection process:
Vehicle Reference Point (VRP): The left intersection point (from the vehicle 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.
Target Reference Point (TRP): This is the bottom-left edge corner of the target, as shown in figure 8.4. Measure the distance between VRP and IRP and note it down.
5. Place the target on RL facing towards the vehicle as shown in Figure 9. The bottom edge of the target should align with the adhesive tape.
6. Measure the distance between IRP and the TRP and note it down.
7. Capture the data from the radar sensor and note down the x, y, and z coordinates of the target with respect to radar and height from the tip of the corner reflector to the ground.
8. We recommend capturing the data from the radar sensor at least 3-5 times for improved accuracy. Move the target to a different position on the Reference line and repeat steps 6 and 7.
Figure 5: Adhesive tape on vehicle edges for front-facing radar
Figure 6: Reference Line 1-5m in front of the vehicle
Figure 7: Vehicle and Intersection Reference Points on tape
Figure 8: Target Reference Point
Figure 9: Target on Reference Line facing towards vehicle
How to paste adhesive tape along the vehicle for different sensor facing directions?
Figure 11: Adhesive tape for front-facing sensor
Figure 12: Adhesive tape for rear-facing sensor
Figure 13: Adhesive tape for left-facing sensor
Figure 10: Adhesive tape for right-facing sensor