/** in place quaternion integration with constant rotational velocity */
void float_quat_integrate(struct FloatQuat *q, struct FloatRates *omega, float dt)
{
const float no = FLOAT_RATES_NORM(*omega);
if (no > FLT_MIN) {
const float a = 0.5 * no * dt;
const float ca = cosf(a);
const float sa_ov_no = sinf(a) / no;
const float dp = sa_ov_no * omega->p;
const float dq = sa_ov_no * omega->q;
const float dr = sa_ov_no * omega->r;
const float qi = q->qi;
const float qx = q->qx;
const float qy = q->qy;
const float qz = q->qz;
q->qi = ca * qi - dp * qx - dq * qy - dr * qz;
q->qx = dp * qi + ca * qx + dr * qy - dq * qz;
q->qy = dq * qi - dr * qx + ca * qy + dp * qz;
q->qz = dr * qi + dq * qx - dp * qy + ca * qz;
}
}
static inline void propagate_ref(void) {
/* converts gyro to floating point */
struct FloatRates gyro_float;
RATES_FLOAT_OF_BFP(gyro_float, imu.gyro_prev);
/* unbias measurement */
RATES_SUB(gyro_float, ahrs_impl.gyro_bias);
#ifdef AHRS_PROPAGATE_LOW_PASS_RATES
/* lowpass angular rates */
const float alpha = 0.1;
FLOAT_RATES_LIN_CMB(ahrs_impl.imu_rate, ahrs_impl.imu_rate,
(1.-alpha), gyro_float, alpha);
#else
RATES_COPY(ahrs_impl.imu_rate, gyro_float);
#endif
/* propagate reference quaternion only if rate is non null */
const float no = FLOAT_RATES_NORM(ahrs_impl.imu_rate);
if (no > FLT_MIN) {
const float dt = 1. / (AHRS_PROPAGATE_FREQUENCY);
const float a = 0.5*no*dt;
const float ca = cosf(a);
const float sa_ov_no = sinf(a)/no;
const float dp = sa_ov_no*ahrs_impl.imu_rate.p;
const float dq = sa_ov_no*ahrs_impl.imu_rate.q;
const float dr = sa_ov_no*ahrs_impl.imu_rate.r;
const float qi = ahrs_impl.ltp_to_imu_quat.qi;
const float qx = ahrs_impl.ltp_to_imu_quat.qx;
const float qy = ahrs_impl.ltp_to_imu_quat.qy;
const float qz = ahrs_impl.ltp_to_imu_quat.qz;
ahrs_impl.ltp_to_imu_quat.qi = ca*qi - dp*qx - dq*qy - dr*qz;
ahrs_impl.ltp_to_imu_quat.qx = dp*qi + ca*qx + dr*qy - dq*qz;
ahrs_impl.ltp_to_imu_quat.qy = dq*qi - dr*qx + ca*qy + dp*qz;
ahrs_impl.ltp_to_imu_quat.qz = dr*qi + dq*qx - dp*qy + ca*qz;
// printf("%f\n", ahrs_impl.ltp_to_imu_quat.qi);
}
}