// update_trig - recalculates _cos_roll, _cos_pitch, etc based on latest attitude
// should be called after _dcm_matrix is updated
void AP_AHRS::update_trig(void)
{
if (_last_trim != _trim.get()) {
_last_trim = _trim.get();
_rotation_autopilot_body_to_vehicle_body.from_euler(_last_trim.x, _last_trim.y, 0.0f);
_rotation_vehicle_body_to_autopilot_body = _rotation_autopilot_body_to_vehicle_body.transposed();
}
Vector2f yaw_vector;
const Matrix3f &temp = get_rotation_body_to_ned();
// sin_yaw, cos_yaw
yaw_vector.x = temp.a.x;
yaw_vector.y = temp.b.x;
yaw_vector.normalize();
_sin_yaw = constrain_float(yaw_vector.y, -1.0, 1.0);
_cos_yaw = constrain_float(yaw_vector.x, -1.0, 1.0);
// cos_roll, cos_pitch
float cx2 = temp.c.x * temp.c.x;
if (cx2 >= 1.0f) {
_cos_pitch = 0;
_cos_roll = 1.0f;
} else {
_cos_pitch = safe_sqrt(1 - cx2);
_cos_roll = temp.c.z / _cos_pitch;
}
_cos_pitch = constrain_float(_cos_pitch, 0, 1.0);
_cos_roll = constrain_float(_cos_roll, -1.0, 1.0); // this relies on constrain_float() of infinity doing the right thing
// sin_roll, sin_pitch
_sin_pitch = -temp.c.x;
if (is_zero(_cos_pitch)) {
_sin_roll = sinf(roll);
} else {
_sin_roll = temp.c.y / _cos_pitch;
}
// sanity checks
if (yaw_vector.is_inf() || yaw_vector.is_nan()) {
yaw_vector.x = 0.0f;
yaw_vector.y = 0.0f;
_sin_yaw = 0.0f;
_cos_yaw = 1.0f;
}
if (isinf(_cos_roll) || isnan(_cos_roll)) {
_cos_roll = cosf(roll);
}
if (isinf(_sin_roll) || isnan(_sin_roll)) {
_sin_roll = sinf(roll);
}
}
// update_trig - recalculates _cos_roll, _cos_pitch, etc based on latest attitude
// should be called after _dcm_matrix is updated
void AP_AHRS::update_trig(void)
{
if (_last_trim != _trim.get()) {
_last_trim = _trim.get();
_rotation_autopilot_body_to_vehicle_body.from_euler(_last_trim.x, _last_trim.y, 0.0f);
_rotation_vehicle_body_to_autopilot_body = _rotation_autopilot_body_to_vehicle_body.transposed();
}
calc_trig(get_rotation_body_to_ned(),
_cos_roll, _cos_pitch, _cos_yaw,
_sin_roll, _sin_pitch, _sin_yaw);
}
/*
* Update AOA and SSA estimation based on airspeed, velocity vector and wind vector
*
* Based on:
* "On estimation of wind velocity, angle-of-attack and sideslip angle of small UAVs using standard sensors" by
* Tor A. Johansen, Andrea Cristofaro, Kim Sorensen, Jakob M. Hansen, Thor I. Fossen
*
* "Multi-Stage Fusion Algorithm for Estimation of Aerodynamic Angles in Mini Aerial Vehicle" by
* C.Ramprasadh and Hemendra Arya
*
* "ANGLE OF ATTACK AND SIDESLIP ESTIMATION USING AN INERTIAL REFERENCE PLATFORM" by
* JOSEPH E. ZEIS, JR., CAPTAIN, USAF
*/
void AP_AHRS::update_AOA_SSA(void)
{
#if APM_BUILD_TYPE(APM_BUILD_ArduPlane)
const uint32_t now = AP_HAL::millis();
if (now - _last_AOA_update_ms < 50) {
// don't update at more than 20Hz
return;
}
_last_AOA_update_ms = now;
Vector3f aoa_velocity, aoa_wind;
// get velocity and wind
if (get_velocity_NED(aoa_velocity) == false) {
return;
}
aoa_wind = wind_estimate();
// Rotate vectors to the body frame and calculate velocity and wind
const Matrix3f &rot = get_rotation_body_to_ned();
aoa_velocity = rot.mul_transpose(aoa_velocity);
aoa_wind = rot.mul_transpose(aoa_wind);
// calculate relative velocity in body coordinates
aoa_velocity = aoa_velocity - aoa_wind;
const float vel_len = aoa_velocity.length();
// do not calculate if speed is too low
if (vel_len < 2.0) {
_AOA = 0;
_SSA = 0;
return;
}
// Calculate AOA and SSA
if (aoa_velocity.x > 0) {
_AOA = degrees(atanf(aoa_velocity.z / aoa_velocity.x));
} else {
_AOA = 0;
}
_SSA = degrees(safe_asin(aoa_velocity.y / vel_len));
#endif
}
// perform drift correction. This function aims to update _omega_P and
// _omega_I with our best estimate of the short term and long term
// gyro error. The _omega_P value is what pulls our attitude solution
// back towards the reference vector quickly. The _omega_I term is an
// attempt to learn the long term drift rate of the gyros.
//
// This drift correction implementation is based on a paper
// by Bill Premerlani from here:
// http://gentlenav.googlecode.com/files/RollPitchDriftCompensation.pdf
void
AP_AHRS_DCM::drift_correction(float deltat)
{
Vector3f velocity;
uint32_t last_correction_time;
// perform yaw drift correction if we have a new yaw reference
// vector
drift_correction_yaw();
const AP_InertialSensor &_ins = AP::ins();
// rotate accelerometer values into the earth frame
for (uint8_t i=0; i<_ins.get_accel_count(); i++) {
if (_ins.get_accel_health(i)) {
/*
by using get_delta_velocity() instead of get_accel() the
accel value is sampled over the right time delta for
each sensor, which prevents an aliasing effect
*/
Vector3f delta_velocity;
_ins.get_delta_velocity(i, delta_velocity);
const float delta_velocity_dt = _ins.get_delta_velocity_dt(i);
if (delta_velocity_dt > 0) {
_accel_ef[i] = _dcm_matrix * (delta_velocity / delta_velocity_dt);
// integrate the accel vector in the earth frame between GPS readings
_ra_sum[i] += _accel_ef[i] * deltat;
}
}
}
//update _accel_ef_blended
if (_ins.get_accel_count() == 2 && _ins.use_accel(0) && _ins.use_accel(1)) {
const float imu1_weight_target = _active_accel_instance == 0 ? 1.0f : 0.0f;
// slew _imu1_weight over one second
_imu1_weight += constrain_float(imu1_weight_target-_imu1_weight, -deltat, deltat);
_accel_ef_blended = _accel_ef[0] * _imu1_weight + _accel_ef[1] * (1.0f - _imu1_weight);
} else {
_accel_ef_blended = _accel_ef[_ins.get_primary_accel()];
}
// keep a sum of the deltat values, so we know how much time
// we have integrated over
_ra_deltat += deltat;
const AP_GPS &_gps = AP::gps();
if (!have_gps() ||
_gps.status() < AP_GPS::GPS_OK_FIX_3D ||
_gps.num_sats() < _gps_minsats) {
// no GPS, or not a good lock. From experience we need at
// least 6 satellites to get a really reliable velocity number
// from the GPS.
//
// As a fallback we use the fixed wing acceleration correction
// if we have an airspeed estimate (which we only have if
// _fly_forward is set), otherwise no correction
if (_ra_deltat < 0.2f) {
// not enough time has accumulated
return;
}
float airspeed;
if (airspeed_sensor_enabled()) {
airspeed = _airspeed->get_airspeed();
} else {
airspeed = _last_airspeed;
}
// use airspeed to estimate our ground velocity in
// earth frame by subtracting the wind
velocity = _dcm_matrix.colx() * airspeed;
// add in wind estimate
velocity += _wind;
last_correction_time = AP_HAL::millis();
_have_gps_lock = false;
} else {
if (_gps.last_fix_time_ms() == _ra_sum_start) {
// we don't have a new GPS fix - nothing more to do
return;
}
velocity = _gps.velocity();
last_correction_time = _gps.last_fix_time_ms();
if (_have_gps_lock == false) {
// if we didn't have GPS lock in the last drift
// correction interval then set the velocities equal
_last_velocity = velocity;
}
_have_gps_lock = true;
// keep last airspeed estimate for dead-reckoning purposes
Vector3f airspeed = velocity - _wind;
// rotate vector to body frame
const Matrix3f &rot = get_rotation_body_to_ned();
airspeed = rot.mul_transpose(airspeed);
// take positive component in X direction. This mimics a pitot
// tube
_last_airspeed = MAX(airspeed.x, 0);
}
if (have_gps()) {
// use GPS for positioning with any fix, even a 2D fix
_last_lat = _gps.location().lat;
_last_lng = _gps.location().lng;
_position_offset_north = 0;
_position_offset_east = 0;
// once we have a single GPS lock, we can update using
// dead-reckoning from then on
_have_position = true;
} else {
// update dead-reckoning position estimate
_position_offset_north += velocity.x * _ra_deltat;
_position_offset_east += velocity.y * _ra_deltat;
}
// see if this is our first time through - in which case we
// just setup the start times and return
if (_ra_sum_start == 0) {
_ra_sum_start = last_correction_time;
_last_velocity = velocity;
return;
}
// equation 9: get the corrected acceleration vector in earth frame. Units
// are m/s/s
Vector3f GA_e(0.0f, 0.0f, -1.0f);
if (_ra_deltat <= 0) {
// waiting for more data
return;
}
bool using_gps_corrections = false;
float ra_scale = 1.0f/(_ra_deltat*GRAVITY_MSS);
if (_flags.correct_centrifugal && (_have_gps_lock || _flags.fly_forward)) {
const float v_scale = gps_gain.get() * ra_scale;
const Vector3f vdelta = (velocity - _last_velocity) * v_scale;
GA_e += vdelta;
GA_e.normalize();
if (GA_e.is_inf()) {
// wait for some non-zero acceleration information
_last_failure_ms = AP_HAL::millis();
return;
}
using_gps_corrections = true;
}
// calculate the error term in earth frame.
// we do this for each available accelerometer then pick the
// accelerometer that leads to the smallest error term. This takes
// advantage of the different sample rates on different
// accelerometers to dramatically reduce the impact of aliasing
// due to harmonics of vibrations that match closely the sampling
// rate of our accelerometers. On the Pixhawk we have the LSM303D
// running at 800Hz and the MPU6000 running at 1kHz, by combining
// the two the effects of aliasing are greatly reduced.
Vector3f error[INS_MAX_INSTANCES];
float error_dirn[INS_MAX_INSTANCES];
Vector3f GA_b[INS_MAX_INSTANCES];
int8_t besti = -1;
float best_error = 0;
for (uint8_t i=0; i<_ins.get_accel_count(); i++) {
if (!_ins.get_accel_health(i)) {
// only use healthy sensors
continue;
}
_ra_sum[i] *= ra_scale;
// get the delayed ra_sum to match the GPS lag
if (using_gps_corrections) {
GA_b[i] = ra_delayed(i, _ra_sum[i]);
} else {
GA_b[i] = _ra_sum[i];
}
if (GA_b[i].is_zero()) {
// wait for some non-zero acceleration information
continue;
}
GA_b[i].normalize();
if (GA_b[i].is_inf()) {
// wait for some non-zero acceleration information
continue;
}
error[i] = GA_b[i] % GA_e;
// Take dot product to catch case vectors are opposite sign and parallel
error_dirn[i] = GA_b[i] * GA_e;
const float error_length = error[i].length();
if (besti == -1 || error_length < best_error) {
besti = i;
best_error = error_length;
}
// Catch case where orientation is 180 degrees out
if (error_dirn[besti] < 0.0f) {
best_error = 1.0f;
}
}
if (besti == -1) {
// no healthy accelerometers!
_last_failure_ms = AP_HAL::millis();
return;
}
_active_accel_instance = besti;
#define YAW_INDEPENDENT_DRIFT_CORRECTION 0
#if YAW_INDEPENDENT_DRIFT_CORRECTION
// step 2 calculate earth_error_Z
const float earth_error_Z = error.z;
// equation 10
const float tilt = norm(GA_e.x, GA_e.y);
// equation 11
const float theta = atan2f(GA_b[besti].y, GA_b[besti].x);
// equation 12
const Vector3f GA_e2 = Vector3f(cosf(theta)*tilt, sinf(theta)*tilt, GA_e.z);
// step 6
error = GA_b[besti] % GA_e2;
error.z = earth_error_Z;
#endif // YAW_INDEPENDENT_DRIFT_CORRECTION
// to reduce the impact of two competing yaw controllers, we
// reduce the impact of the gps/accelerometers on yaw when we are
// flat, but still allow for yaw correction using the
// accelerometers at high roll angles as long as we have a GPS
if (AP_AHRS_DCM::use_compass()) {
if (have_gps() && is_equal(gps_gain.get(), 1.0f)) {
error[besti].z *= sinf(fabsf(roll));
} else {
error[besti].z = 0;
}
}
// if ins is unhealthy then stop attitude drift correction and
// hope the gyros are OK for a while. Just slowly reduce _omega_P
// to prevent previous bad accels from throwing us off
if (!_ins.healthy()) {
error[besti].zero();
} else {
// convert the error term to body frame
error[besti] = _dcm_matrix.mul_transpose(error[besti]);
}
if (error[besti].is_nan() || error[besti].is_inf()) {
// don't allow bad values
check_matrix();
_last_failure_ms = AP_HAL::millis();
return;
}
_error_rp = 0.8f * _error_rp + 0.2f * best_error;
// base the P gain on the spin rate
const float spin_rate = _omega.length();
// sanity check _kp value
if (_kp < AP_AHRS_RP_P_MIN) {
_kp = AP_AHRS_RP_P_MIN;
}
// we now want to calculate _omega_P and _omega_I. The
// _omega_P value is what drags us quickly to the
// accelerometer reading.
_omega_P = error[besti] * _P_gain(spin_rate) * _kp;
if (use_fast_gains()) {
_omega_P *= 8;
}
if (_flags.fly_forward && _gps.status() >= AP_GPS::GPS_OK_FIX_2D &&
_gps.ground_speed() < GPS_SPEED_MIN &&
_ins.get_accel().x >= 7 &&
pitch_sensor > -3000 && pitch_sensor < 3000) {
// assume we are in a launch acceleration, and reduce the
// rp gain by 50% to reduce the impact of GPS lag on
// takeoff attitude when using a catapult
_omega_P *= 0.5f;
}
// accumulate some integrator error
if (spin_rate < ToRad(SPIN_RATE_LIMIT)) {
_omega_I_sum += error[besti] * _ki * _ra_deltat;
_omega_I_sum_time += _ra_deltat;
}
if (_omega_I_sum_time >= 5) {
// limit the rate of change of omega_I to the hardware
// reported maximum gyro drift rate. This ensures that
// short term errors don't cause a buildup of omega_I
// beyond the physical limits of the device
const float change_limit = _gyro_drift_limit * _omega_I_sum_time;
_omega_I_sum.x = constrain_float(_omega_I_sum.x, -change_limit, change_limit);
_omega_I_sum.y = constrain_float(_omega_I_sum.y, -change_limit, change_limit);
_omega_I_sum.z = constrain_float(_omega_I_sum.z, -change_limit, change_limit);
_omega_I += _omega_I_sum;
_omega_I_sum.zero();
_omega_I_sum_time = 0;
}
// zero our accumulator ready for the next GPS step
memset((void *)&_ra_sum[0], 0, sizeof(_ra_sum));
_ra_deltat = 0;
_ra_sum_start = last_correction_time;
// remember the velocity for next time
_last_velocity = velocity;
}
