imu bias noise unit

[narutojxl]

Hi doctor qin, In lins paper, imu bias's derivates n_ba, n_bg unit are m/(s^2)/s and rad/s/s repectively? In cofig file exp_port.yaml:

• acc_w is n_ba. acc_w's unit is *ug/s = 1e-6 9.81 m/(s^2)/s**.
• gyr_w is n_bg. gyr_w's unit is degree/sqrt(h) = pi/180.0/sqrt(3600) rad/sqrt(s), which is not consistent with the paper?

I'm confused with the imu bias noise unit. I want to figure out the 4 noise terms unit and then figure out how to set them value according to a imu datasheet. Please have a look when you are free, thanks a lot !

[narutojxl]

Hi @qin, Could you give a description in README about the default units of imu noise used in code ? Thanks a lot !

[ChaoqinRobotics]

Hi @narutojxl . Sorry for replying late. I directly follow the imu bias natation convention from Principles of GNSS, Inertial, and Multisensor Integrated Navigation Systems written by Paul D Groves.

Their definitions are:

• acc_w: Accelerometer noise root PSD (micro-g per root Hz, converted to m s^-1.5)
  e.g. IMU_errors.accel_noise_root_PSD = 100 * 9.80665E-6;
• gyr_w: Gyro noise root PSD (deg per root hour, converted to rad s^-0.5)
  e.g. IMU_errors.gyro_noise_root_PSD = 0.01 * deg_to_rad / 60;

[narutojxl]

It doesn't matter, thanks @qin :) I will read the reference paper tomorrow.

[narutojxl]

Hi @qin,

• For acc_w, convert ug/sqrt(Hz) into m s^-1.5, in code, we do not multiply the front coefficient 100.
• For gyr_w, convert deg/sqrt(hr) into rad s^-0.5 in code, we do not multiply the front coefficient 0.01.

In reference book, it suggest we need to multiply root PSD with sqrt(Hz), do we need to do this in code?

[Liming-Cheng]

Hi @narutojxl , Do you solve the problem about imu parameter ? In the UrbanNav dataset, the unit of acc_noise and acc_walk is m/(s^2), and gyro_noise is rad/s. Should I do any special treatment in the config file? Here is imu parameters in UrbanNavdataset https://github.com/weisongwen/UrbanNavDataset/blob/master/UrbanNav-HK-Data20190428/xsens_imu_param.yaml.

[narutojxl]

Hi @Liming-Cheng, According to author given the reference paper,

bias unit acc_w: Accelerometer noise root PSD (micro-g per root Hz, converted to m s^-1.5), gyr_w: Gyro noise root PSD (deg per root hour, converted to rad s^-0.5)

It seems that above value should be multiply with the root of the sampling rate, when using. Imu parameters in UrbanNavdataset seems got from https://github.com/gaowenliang/imu_utils. I am not sure whether we can directly use these params in lins code, maybe we should do some convertion as you said, look forward author qin can give a explanation :)

[fengxingyang]

Hi @narutojxl, I encountered some difficulties in trying to run Lins with the Kitti dataset,the topic of laser_odom_to_init and the topic of aft_mapped_to_init deviate too far in rviz,I have revised the contents of the exp_port.yaml as follows,What's wrong with me? ![Uploading 2021-02-19 21-26-28屏幕截图.png…]()