README.md

IMU_EKF

This is a C++ implementation of an Error State Kalman Filter or Multiplicative Kalman Filter roughly based on Attitude Error Representations for Kalman Filtering by Landis Markley suitable for platform.io projects to fuse IMU measurements (gyroscope, accelerometer and magnetometer). In contrast to the paper I extended the state to x,y,z position, x,y,z velocities and x,y,z accelerations. Be aware that the linear velocity and position estimates are of no use. I included them just as an experiment. Instead of the gyro drift I added the angular velocity to the state. Also I use the quaternion to rotation matrix transformation from Euclideanspace.

Dependencies

This implementation depends on Eigen. For platform.io projects you can use Eigen_Platformio_Header.

Usage

#include <Eigen.h>
#include <ESKF.h>
#include <Quaternion.h>

// magnetometer calibration
Eigen::Matrix<float, 3, 3> W; // soft-iron
Eigen::Matrix<float, 3, 1> V; // hard-iron
float incl; // inclination
float B; // geomagnetic field strength

IMU_EKF::ESKF<float> filter;

void setup()
{
    // fill magnetometer calibration stuff
    // Winv << 
    // W << 
    // B = 
    // incl = 

    float ax, ay, az;
    // read accelerometer
    filter.initWithAcc(ax, ay, az);
}

void loop()
{
    float dt;
    bool readMag; // assume magnetometer has lower update rate as acellerometer and gyroscope

    // calculate dt

    // read sensors

    filter.predict(dt);
    filter.correctGyr(gx, gy, gz);
    filter.correctAcc(ax, ay, az);
    if (readMag)
    {
        filter.correctMag(mx, my, mz, incl, B, W, V);
    }
    filter.reset();

    // get attitude as roll, pitch, yaw
    float roll, pitch, yaw;
    filter.getAttitude(roll, pitch, yaw);
    // or quaternion
    IMU_EKF::Quaternion<float> q = filter.getAttitude();
}