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ardupilot/libraries/AP_AHRS/AP_AHRS_Quaternion.cpp

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/*
AP_AHRS_Quaternion code, based on quaternion code from Jeb Madgwick
See http://www.x-io.co.uk/res/doc/madgwick_internal_report.pdf
adapted to APM by Andrew Tridgell based on initial idea,
discussions and prototype from Justin Beech.
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later
version.
*/
#include <FastSerial.h>
#include <AP_AHRS.h>
// to keep the code as close to the original as possible, we use these
// macros for quaternion access
#define SEq_1 q.q1
#define SEq_2 q.q2
#define SEq_3 q.q3
#define SEq_4 q.q4
// Function to compute one quaternion iteration without magnetometer
void AP_AHRS_Quaternion::update_IMU(float deltat, Vector3f &gyro, Vector3f &accel)
{
// Local system variables
float norm; // vector norm
float SEqDot_omega_1, SEqDot_omega_2, SEqDot_omega_3, SEqDot_omega_4; // quaternion derrivative from gyroscopes elements
float f_1, f_2, f_3; // objective function elements
float J_11or24, J_12or23, J_13or22, J_14or21, J_32, J_33; // objective function Jacobian elements
float SEqHatDot_1, SEqHatDot_2, SEqHatDot_3, SEqHatDot_4; // estimated direction of the gyroscope error
// Axulirary variables to avoid reapeated calcualtions
float halfSEq_1 = 0.5f * SEq_1;
float halfSEq_2 = 0.5f * SEq_2;
float halfSEq_3 = 0.5f * SEq_3;
float halfSEq_4 = 0.5f * SEq_4;
float twoSEq_1 = 2.0f * SEq_1;
float twoSEq_2 = 2.0f * SEq_2;
float twoSEq_3 = 2.0f * SEq_3;
// estimated direction of the gyroscope error (radians)
Vector3f w_err;
// normalise accelerometer vector
accel.normalize();
if (accel.is_inf()) {
// discard this data point
renorm_range_count++;
return;
}
// Compute the objective function and Jacobian
f_1 = twoSEq_2 * SEq_4 - twoSEq_1 * SEq_3 - accel.x;
f_2 = twoSEq_1 * SEq_2 + twoSEq_3 * SEq_4 - accel.y;
f_3 = 1.0f - twoSEq_2 * SEq_2 - twoSEq_3 * SEq_3 - accel.z;
J_11or24 = twoSEq_3; // J_11 negated in matrix multiplication
J_12or23 = 2.0f * SEq_4;
J_13or22 = twoSEq_1; // J_12 negated in matrix multiplication
J_14or21 = twoSEq_2;
J_32 = 2.0f * J_14or21; // negated in matrix multiplication
J_33 = 2.0f * J_11or24; // negated in matrix multiplication
// Compute the gradient (matrix multiplication)
SEqHatDot_1 = J_14or21 * f_2 - J_11or24 * f_1;
SEqHatDot_2 = J_12or23 * f_1 + J_13or22 * f_2 - J_32 * f_3;
SEqHatDot_3 = J_12or23 * f_2 - J_33 * f_3 - J_13or22 * f_1;
SEqHatDot_4 = J_14or21 * f_1 + J_11or24 * f_2;
// Normalise the gradient
norm = 1.0/safe_sqrt(SEqHatDot_1 * SEqHatDot_1 + SEqHatDot_2 * SEqHatDot_2 + SEqHatDot_3 * SEqHatDot_3 + SEqHatDot_4 * SEqHatDot_4);
if (isinf(norm)) {
// we can't do an update - discard this data point and
// hope the next one is better
renorm_range_count++;
return;
}
SEqHatDot_1 *= norm;
SEqHatDot_2 *= norm;
SEqHatDot_3 *= norm;
SEqHatDot_4 *= norm;
// Compute the quaternion derrivative measured by gyroscopes
SEqDot_omega_1 = -halfSEq_2 * gyro.x - halfSEq_3 * gyro.y - halfSEq_4 * gyro.z;
SEqDot_omega_2 = halfSEq_1 * gyro.x + halfSEq_3 * gyro.z - halfSEq_4 * gyro.y;
SEqDot_omega_3 = halfSEq_1 * gyro.y - halfSEq_2 * gyro.z + halfSEq_4 * gyro.x;
SEqDot_omega_4 = halfSEq_1 * gyro.z + halfSEq_2 * gyro.y - halfSEq_3 * gyro.x;
// Compute then integrate the estimated quaternion derrivative
SEq_1 += (SEqDot_omega_1 - (beta * SEqHatDot_1)) * deltat;
SEq_2 += (SEqDot_omega_2 - (beta * SEqHatDot_2)) * deltat;
SEq_3 += (SEqDot_omega_3 - (beta * SEqHatDot_3)) * deltat;
SEq_4 += (SEqDot_omega_4 - (beta * SEqHatDot_4)) * deltat;
// Normalise quaternion
norm = 1.0/safe_sqrt(SEq_1 * SEq_1 + SEq_2 * SEq_2 + SEq_3 * SEq_3 + SEq_4 * SEq_4);
if (isinf(norm)) {
// our quaternion is bad! Reset based on roll/pitch/yaw
// and hope for the best ...
renorm_blowup_count++;
q.from_euler(roll, pitch, yaw);
return;
}
SEq_1 *= norm;
SEq_2 *= norm;
SEq_3 *= norm;
SEq_4 *= norm;
}
// Function to compute one quaternion iteration including magnetometer
void AP_AHRS_Quaternion::update_MARG(float deltat, Vector3f &gyro, Vector3f &accel, Vector3f &mag)
{
// local system variables
float norm; // vector norm
float SEqDot_omega_1, SEqDot_omega_2, SEqDot_omega_3, SEqDot_omega_4; // quaternion rate from gyroscopes elements
float f_1, f_2, f_3, f_4, f_5, f_6; // objective function elements
float J_11or24, J_12or23, J_13or22, J_14or21, J_32, J_33, // objective function Jacobian elements
J_41, J_42, J_43, J_44, J_51, J_52, J_53, J_54, J_61, J_62, J_63, J_64; //
float SEqHatDot_1, SEqHatDot_2, SEqHatDot_3, SEqHatDot_4; // estimated direction of the gyroscope error
// computed flux in the earth frame
Vector3f flux;
// estimated direction of the gyroscope error (radians)
Vector3f w_err;
// normalise accelerometer vector
accel.normalize();
if (accel.is_inf()) {
// discard this data point
renorm_range_count++;
return;
}
// normalise the magnetometer measurement
mag.normalize();
if (mag.is_inf()) {
// discard this data point
renorm_range_count++;
return;
}
// auxiliary variables to avoid repeated calculations
float halfSEq_1 = 0.5f * SEq_1;
float halfSEq_2 = 0.5f * SEq_2;
float halfSEq_3 = 0.5f * SEq_3;
float halfSEq_4 = 0.5f * SEq_4;
float twoSEq_1 = 2.0f * SEq_1;
float twoSEq_2 = 2.0f * SEq_2;
float twoSEq_3 = 2.0f * SEq_3;
float twoSEq_4 = 2.0f * SEq_4;
float twob_x = 2.0f * b_x;
float twob_z = 2.0f * b_z;
float twob_xSEq_1 = 2.0f * b_x * SEq_1;
float twob_xSEq_2 = 2.0f * b_x * SEq_2;
float twob_xSEq_3 = 2.0f * b_x * SEq_3;
float twob_xSEq_4 = 2.0f * b_x * SEq_4;
float twob_zSEq_1 = 2.0f * b_z * SEq_1;
float twob_zSEq_2 = 2.0f * b_z * SEq_2;
float twob_zSEq_3 = 2.0f * b_z * SEq_3;
float twob_zSEq_4 = 2.0f * b_z * SEq_4;
float SEq_1SEq_2;
float SEq_1SEq_3 = SEq_1 * SEq_3;
float SEq_1SEq_4;
float SEq_2SEq_3;
float SEq_2SEq_4 = SEq_2 * SEq_4;
float SEq_3SEq_4;
Vector3f twom = mag * 2.0;
// compute the objective function and Jacobian
f_1 = twoSEq_2 * SEq_4 - twoSEq_1 * SEq_3 - accel.x;
f_2 = twoSEq_1 * SEq_2 + twoSEq_3 * SEq_4 - accel.y;
f_3 = 1.0f - twoSEq_2 * SEq_2 - twoSEq_3 * SEq_3 - accel.z;
f_4 = twob_x * (0.5f - SEq_3 * SEq_3 - SEq_4 * SEq_4) + twob_z * (SEq_2SEq_4 - SEq_1SEq_3) - mag.x;
f_5 = twob_x * (SEq_2 * SEq_3 - SEq_1 * SEq_4) + twob_z * (SEq_1 * SEq_2 + SEq_3 * SEq_4) - mag.y;
f_6 = twob_x * (SEq_1SEq_3 + SEq_2SEq_4) + twob_z * (0.5f - SEq_2 * SEq_2 - SEq_3 * SEq_3) - mag.z;
J_11or24 = twoSEq_3; // J_11 negated in matrix multiplication
J_12or23 = 2.0f * SEq_4;
J_13or22 = twoSEq_1; // J_12 negated in matrix multiplication
J_14or21 = twoSEq_2;
J_32 = 2.0f * J_14or21; // negated in matrix multiplication
J_33 = 2.0f * J_11or24; // negated in matrix multiplication
J_41 = twob_zSEq_3; // negated in matrix multiplication
J_42 = twob_zSEq_4;
J_43 = 2.0f * twob_xSEq_3 + twob_zSEq_1; // negated in matrix multiplication
J_44 = 2.0f * twob_xSEq_4 - twob_zSEq_2; // negated in matrix multiplication
J_51 = twob_xSEq_4 - twob_zSEq_2; // negated in matrix multiplication
J_52 = twob_xSEq_3 + twob_zSEq_1;
J_53 = twob_xSEq_2 + twob_zSEq_4;
J_54 = twob_xSEq_1 - twob_zSEq_3; // negated in matrix multiplication
J_61 = twob_xSEq_3;
J_62 = twob_xSEq_4 - 2.0f * twob_zSEq_2;
J_63 = twob_xSEq_1 - 2.0f * twob_zSEq_3;
J_64 = twob_xSEq_2;
// compute the gradient (matrix multiplication)
SEqHatDot_1 = J_14or21 * f_2 - J_11or24 * f_1 - J_41 * f_4 - J_51 * f_5 + J_61 * f_6;
SEqHatDot_2 = J_12or23 * f_1 + J_13or22 * f_2 - J_32 * f_3 + J_42 * f_4 + J_52 * f_5 + J_62 * f_6;
SEqHatDot_3 = J_12or23 * f_2 - J_33 * f_3 - J_13or22 * f_1 - J_43 * f_4 + J_53 * f_5 + J_63 * f_6;
SEqHatDot_4 = J_14or21 * f_1 + J_11or24 * f_2 - J_44 * f_4 - J_54 * f_5 + J_64 * f_6;
// normalise the gradient to estimate direction of the gyroscope error
norm = 1.0 / safe_sqrt(SEqHatDot_1 * SEqHatDot_1 + SEqHatDot_2 * SEqHatDot_2 + SEqHatDot_3 * SEqHatDot_3 + SEqHatDot_4 * SEqHatDot_4);
if (isinf(norm)) {
// discard this data point
renorm_range_count++;
return;
}
SEqHatDot_1 *= norm;
SEqHatDot_2 *= norm;
SEqHatDot_3 *= norm;
SEqHatDot_4 *= norm;
// compute angular estimated direction of the gyroscope error
w_err.x = twoSEq_1 * SEqHatDot_2 - twoSEq_2 * SEqHatDot_1 - twoSEq_3 * SEqHatDot_4 + twoSEq_4 * SEqHatDot_3;
w_err.y = twoSEq_1 * SEqHatDot_3 + twoSEq_2 * SEqHatDot_4 - twoSEq_3 * SEqHatDot_1 - twoSEq_4 * SEqHatDot_2;
w_err.z = twoSEq_1 * SEqHatDot_4 - twoSEq_2 * SEqHatDot_3 + twoSEq_3 * SEqHatDot_2 - twoSEq_4 * SEqHatDot_1;
// keep track of the error rates
_error_rp_sum += 0.5*(fabs(w_err.x) + fabs(w_err.y));
_error_yaw_sum += fabs(w_err.z);
_error_rp_count++;
_error_yaw_count++;
// compute the gyroscope bias delta
Vector3f drift_delta = w_err * (deltat * zeta);
// don't allow the drift rate to be exceeded. This prevents a
// sudden drift change coming from a outage in the compass
float max_change = _gyro_drift_limit * deltat;
drift_delta.x = constrain(drift_delta.x, -max_change, max_change);
drift_delta.y = constrain(drift_delta.y, -max_change, max_change);
drift_delta.z = constrain(drift_delta.z, -max_change, max_change);
gyro_bias += drift_delta;
// correct the gyro reading for drift
gyro -= gyro_bias;
// compute the quaternion rate measured by gyroscopes
SEqDot_omega_1 = -halfSEq_2 * gyro.x - halfSEq_3 * gyro.y - halfSEq_4 * gyro.z;
SEqDot_omega_2 = halfSEq_1 * gyro.x + halfSEq_3 * gyro.z - halfSEq_4 * gyro.y;
SEqDot_omega_3 = halfSEq_1 * gyro.y - halfSEq_2 * gyro.z + halfSEq_4 * gyro.x;
SEqDot_omega_4 = halfSEq_1 * gyro.z + halfSEq_2 * gyro.y - halfSEq_3 * gyro.x;
// compute then integrate the estimated quaternion rate
SEq_1 += (SEqDot_omega_1 - (beta * SEqHatDot_1)) * deltat;
SEq_2 += (SEqDot_omega_2 - (beta * SEqHatDot_2)) * deltat;
SEq_3 += (SEqDot_omega_3 - (beta * SEqHatDot_3)) * deltat;
SEq_4 += (SEqDot_omega_4 - (beta * SEqHatDot_4)) * deltat;
// normalise quaternion
norm = 1.0/safe_sqrt(SEq_1 * SEq_1 + SEq_2 * SEq_2 + SEq_3 * SEq_3 + SEq_4 * SEq_4);
if (isinf(norm)) {
// our quaternion is bad! Reset based on roll/pitch/yaw
// and hope for the best ...
renorm_blowup_count++;
q.from_euler(roll, pitch, yaw);
return;
}
SEq_1 *= norm;
SEq_2 *= norm;
SEq_3 *= norm;
SEq_4 *= norm;
// compute flux in the earth frame
// recompute axulirary variables
SEq_1SEq_2 = SEq_1 * SEq_2;
SEq_1SEq_3 = SEq_1 * SEq_3;
SEq_1SEq_4 = SEq_1 * SEq_4;
SEq_3SEq_4 = SEq_3 * SEq_4;
SEq_2SEq_3 = SEq_2 * SEq_3;
SEq_2SEq_4 = SEq_2 * SEq_4;
flux.x = twom.x * (0.5f - SEq_3 * SEq_3 - SEq_4 * SEq_4) + twom.y * (SEq_2SEq_3 - SEq_1SEq_4) + twom.z * (SEq_2SEq_4 + SEq_1SEq_3);
flux.y = twom.x * (SEq_2SEq_3 + SEq_1SEq_4) + twom.y * (0.5f - SEq_2 * SEq_2 - SEq_4 * SEq_4) + twom.z * (SEq_3SEq_4 - SEq_1SEq_2);
flux.z = twom.x * (SEq_2SEq_4 - SEq_1SEq_3) + twom.y * (SEq_3SEq_4 + SEq_1SEq_2) + twom.z * (0.5f - SEq_2 * SEq_2 - SEq_3 * SEq_3);
// normalise the flux vector to have only components in the x and z
b_x = sqrt((flux.x * flux.x) + (flux.y * flux.y));
b_z = flux.z;
}
// Function to compute one quaternion iteration
void AP_AHRS_Quaternion::update(void)
{
Vector3f gyro, accel;
float deltat;
_imu->update();
deltat = _imu->get_delta_time();
if (deltat > 1.0) {
// if we stop updating for 1s, we should discard this
// input data. This can happen if you are running the
// code under a debugger, and using this data point
// will just throw off your attitude by a huge amount
return;
}
if (!_have_initial_yaw && _compass &&
_compass->use_for_yaw()) {
// setup the quaternion with initial compass yaw
q.from_euler(0, 0, _compass->calculate_heading(0,0));
_have_initial_yaw = true;
_compass_last_update = _compass->last_update;
gyro_bias.zero();
}
// get current IMU state
gyro = _imu->get_gyro();
// the quaternion system uses opposite sign for accel
accel = - _imu->get_accel();
if (_fly_forward && _gps && _gps->status() == GPS::GPS_OK) {
// compensate for centripetal acceleration
float veloc;
veloc = _gps->ground_speed * 0.01;
// be careful of the signs in this calculation. the
// quaternion system uses different signs than the
// rest of APM
accel.y += (gyro.z - gyro_bias.z) * veloc;
accel.z -= (gyro.y - gyro_bias.y) * veloc;
}
if (_compass != NULL && _compass->use_for_yaw()) {
Vector3f mag = Vector3f(_compass->mag_x, _compass->mag_y, _compass->mag_z);
update_MARG(deltat, gyro, accel, mag);
} else {
// step the quaternion solution using just gyros and accels
gyro -= gyro_bias;
update_IMU(deltat, gyro, accel);
}
#ifdef DESKTOP_BUILD
if (q.is_nan()) {
SITL_debug("QUAT NAN: deltat=%f roll=%f pitch=%f yaw=%f q=[%f %f %f %f] a=[%f %f %f] g=(%f %f %f)\n",
deltat, roll, pitch, yaw,
q.q1, q.q2, q.q3, q.q4,
accel.x, accel.y, accel.z,
gyro.x, gyro.y, gyro.z);
}
#endif
// keep the corrected gyro for reporting
_gyro_corrected = gyro;
// calculate our euler angles for high level control and navigation
q.to_euler(&roll, &pitch, &yaw);
// the code above assumes zero magnetic declination, so offset
// the yaw here
if (_compass != NULL) {
yaw += _compass->get_declination();
}
// and integer Eulers
roll_sensor = 100 * ToDeg(roll);
pitch_sensor = 100 * ToDeg(pitch);
yaw_sensor = 100 * ToDeg(yaw);
if (yaw_sensor < 0) {
yaw_sensor += 36000;
}
}
/* reporting of Quaternion state for MAVLink */
// average error_roll_pitch since last call
float AP_AHRS_Quaternion::get_error_rp(void)
{
if (_error_rp_count == 0) {
// this happens when telemetry is setup on two
// serial ports
return _error_rp_last;
}
_error_rp_last = _error_rp_sum / _error_rp_count;
_error_rp_sum = 0;
_error_rp_count = 0;
return _error_rp_last;
}
// average error_yaw since last call
float AP_AHRS_Quaternion::get_error_yaw(void)
{
if (_error_yaw_count == 0) {
// this happens when telemetry is setup on two
// serial ports
return _error_yaw_last;
}
_error_yaw_last = _error_yaw_sum / _error_yaw_count;
_error_yaw_sum = 0;
_error_yaw_count = 0;
return _error_yaw_last;
}
// reset attitude system
void AP_AHRS_Quaternion::reset(bool recover_eulers)
{
if (recover_eulers) {
q.from_euler(roll, pitch, yaw);
} else {
q(1, 0, 0, 0);
}
gyro_bias.zero();
// reference direction of flux in earth frame
b_x = 0;
b_z = -1;
}
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