# Allan Variance ROS

## ROS package which loads a rosbag of IMU data and computes Allan Variance parameters

The purpose of this tool is to read a long sequence of IMU data and return the Angle Random Walk (ARW), Bias Instability and Random Walk for the gyroscope as well as Velocity Random Walk (VRW), Bias Instability and Random Walk for the accelerometer.

### How to use

Build the package:

`catkin build allan_variance_ros`

**Recommended:** Reorganize ROS messages by timestamp using ROS Cookbook:

`rosrun allan_variance_ros cookbag.py --input original_rosbag --output cooked_rosbag`

Run the Allan Variance computation tool:

`rosrun allan_variance_ros allan_variance [path_to_rosbags] [path_to_config_file]`

This will compute the Allan Deviation for the IMU and generate a CSV. The next step is to visualize the plots and get parameters. For this run:

`rosrun allan_variance_ros analysis.py --data allan_variance.csv`

Press `space`

to go to next figure.

### How to collect sequence

Place your IMU on some damped surface and record your IMU data to a rosbag. You must record **at least** 3 hours of data. The longer the sequence, the more accurate the results.

### Example Log

3 hour log of Realsense D435i IMU already "cooked".

Example terminal output:

```
ACCELEROMETER:
X Velocity Random Walk: 0.00333 m/s/sqrt(s) 0.19983 m/s/sqrt(hr)
Y Velocity Random Walk: 0.01079 m/s/sqrt(s) 0.64719 m/s/sqrt(hr)
Z Velocity Random Walk: 0.00481 m/s/sqrt(s) 0.28846 m/s/sqrt(hr)
X Bias Instability: 0.00055 m/s^2 1.99258 m/hr^2
Y Bias Instability: 0.00153 m/s^2 5.51917 m/hr^2
Z Bias Instability: 0.00052 m/s^2 1.86155 m/hr^2
X Accel Random Walk: 0.00008 m/s^2
Y Accel Random Walk: 0.00020 m/s^2
Z Accel Random Walk: 0.00007 m/s^2
GYROSCOPE:
X Angle Random Walk: 0.00787 deg/sqrt(s) 0.47215 deg/sqrt(hr)
Y Angle Random Walk: 0.00987 deg/sqrt(s) 0.59204 deg/sqrt(hr)
Z Angle Random Walk: 0.00839 deg/sqrt(s) 0.50331 deg/sqrt(hr)
X Bias Instability: 0.00049 deg/s 1.76568 deg/hr
Y Bias Instability: 0.00136 deg/s 4.88153 deg/hr
Z Bias Instability: 0.00088 deg/s 3.15431 deg/hr
X Rate Random Walk: 0.00007 deg/s
Y Rate Random Walk: 0.00028 deg/s
Z Rate Random Walk: 0.00011 deg/s
```

### Kalibr

Kalibr is a useful collection of tools for calibrating cameras and IMUs. For IMU calibration it needs the noise parameters of the IMU generated in a yaml file. `allan_variance_ros`

automatically generates this file file as `imu.yaml`

:

```
#Accelerometer
accelerometer_noise_density: 0.006308226052016165
accelerometer_random_walk: 0.00011673723527962174
#Gyroscope
gyroscope_noise_density: 0.00015198973532354657
gyroscope_random_walk: 2.664506559330434e-06
rostopic: '/sensors/imu' #Make sure this is correct
update_rate: 400.0 #Make sure this is correct
```