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Taeyoung96 / GRIL-Calib

[RA-L 2024] GRIL-Calib: Targetless Ground Robot IMU-LiDAR Extrinsic Calibration Method using Ground Plane Motion Constraints
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x,y,z_accumulate and Impact on accuracy #5

Open momoistda opened 1 month ago

momoistda commented 1 month ago

Hello, Thanks for posting this nice method! I have two questions:

  1. In the config fiel, we should give the x,y,z_accumulate:

x_accumulate: Parameter that determines how much the x-axis rotates (Assuming the x-axis is front) y_accumulate: Parameter that determines how much the y-axis rotates (Assuming the y-axis is left) z_accumulate: Parameter that determines how much the z-axis rotates (Assuming the z-axis is up)

SO, If my y-axis is positiv to the right, should i fill in 0.999?

2. Are there any time limit and path requirements (like how lang should the path of this figure 8 shape be?) for data collection? I used same robot with same speed, but output parameters are very different. See below, data1 and data2 were collected in same place:

data1: LiDAR-IMU calibration result: Rotation LiDAR to IMU (degree) = -3.664754 0.884811 -7.481670 Translation LiDAR to IMU (meter) = -0.445991 -0.568093 -0.098269 Time Lag IMU to LiDAR (second) = -2.458705 Bias of Gyroscope (rad/s) = -0.010000 0.010000 0.010000 Bias of Accelerometer (meters/s^2) = -0.008860 0.010584 -0.010463

Homogeneous Transformation Matrix from LiDAR frmae L to IMU frame I: 0.991370 0.128955 0.023600 -0.445991 -0.130184 0.989589 0.061363 -0.568093 -0.015441 -0.063906 0.997836 -0.098269 0.000000 0.000000 0.000000 1.000000

data2: LiDAR-IMU calibration result: Rotation LiDAR to IMU (degree) = -0.514068 -0.272551 10.003449 Translation LiDAR to IMU (meter) = 0.279931 -1.056407 -0.092049 Time Lag IMU to LiDAR (second) = 0.659137 Bias of Gyroscope (rad/s) = -0.010000 0.010000 0.002501 Bias of Accelerometer (meters/s^2) = -0.008049 -0.011665 -0.009957

Homogeneous Transformation Matrix from LiDAR frmae L to IMU frame I: 0.984788 -0.173646 -0.006242 0.279931 0.173693 0.984767 0.008009 -1.056407 0.004757 -0.008971 0.999948 -0.092049 0.000000 0.000000 0.000000 1.000000

Taeyoung96 commented 1 month ago

@momoistda Thanks for interesting our work!

  1. If you're confused about the axes, we suggest experimenting with 0.999 for all x_accumulate, y_accumulate, and z_accumulate first, and then re-enter x_accumulate, y_accumulate, and z_accumulate using the percentages in the terminal when you're done collecting data.
    For example, if the output to the terminal at the end of a data collection is ""Rotation around Lidar X Axis: 70%", then the correct value for the data collection you have now is x_accumulate of 0.7.

  2. Unfortunately, the exact time to collect data was not covered in this research.
    Did you set your config file differently? The gyro_factor, acc_factor, and ground_factor can cause different results.

momoistda commented 1 month ago

@Taeyoung96 Thank you very much for your answer. For 1: I use the GRIL-Calib for off-line calibration. For example, if I get the information from the terminal during the calibration like this:

gril_calib

That means, x_accumulate is 29% or 100%? Because it shows like "Rotation around Lidar X Axis complete!"

For 2. no, i just used the standard value from the velodyne16.yaml file.