ardupilot/libraries/AP_InertialNav/AP_InertialNav.cpp

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/// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
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#include <AP_HAL.h>
#include <AP_InertialNav.h>
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extern const AP_HAL::HAL& hal;
// table of user settable parameters
const AP_Param::GroupInfo AP_InertialNav::var_info[] PROGMEM = {
// start numbering at 1 because 0 was previous used for body frame accel offsets
// @Param: TC_XY
// @DisplayName: Horizontal Time Constant
// @Description: Time constant for GPS and accel mixing. Higher TC decreases GPS impact on position estimate
// @Range: 0 10
// @Increment: 0.1
AP_GROUPINFO("TC_XY", 1, AP_InertialNav, _time_constant_xy, AP_INTERTIALNAV_TC_XY),
// @Param: TC_Z
// @DisplayName: Vertical Time Constant
// @Description: Time constant for baro and accel mixing. Higher TC decreases barometers impact on altitude estimate
// @Range: 0 10
// @Increment: 0.1
AP_GROUPINFO("TC_Z", 2, AP_InertialNav, _time_constant_z, AP_INTERTIALNAV_TC_Z),
AP_GROUPEND
};
// init - initialise library
void AP_InertialNav::init()
{
// recalculate the gains
update_gains();
}
// update - updates velocities and positions using latest info from ahrs and barometer if new data is available;
void AP_InertialNav::update(float dt)
{
// discard samples where dt is too large
if( dt > 0.1f ) {
return;
}
// decrement ignore error count if required
if (_flags.ignore_error > 0) {
_flags.ignore_error--;
}
// check if new baro readings have arrived and use them to correct vertical accelerometer offsets.
check_baro();
// check if new gps readings have arrived and use them to correct position estimates
check_gps();
Vector3f accel_ef = _ahrs.get_accel_ef();
// remove influence of gravity
accel_ef.z += GRAVITY_MSS;
accel_ef *= 100;
// remove xy if not enabled
if( !_xy_enabled ) {
accel_ef.x = 0;
accel_ef.y = 0;
}
//Convert North-East-Down to North-East-Up
accel_ef.z = -accel_ef.z;
float tmp = _k3_xy * dt;
accel_correction_ef.x += _position_error.x * tmp;
accel_correction_ef.y += _position_error.y * tmp;
accel_correction_ef.z += _position_error.z * _k3_z * dt;
tmp = _k2_xy * dt;
_velocity.x += _position_error.x * tmp;
_velocity.y += _position_error.y * tmp;
_velocity.z += _position_error.z * _k2_z * dt;
tmp = _k1_xy * dt;
_position_correction.x += _position_error.x * tmp;
_position_correction.y += _position_error.y * tmp;
_position_correction.z += _position_error.z * _k1_z * dt;
// calculate velocity increase adding new acceleration from accelerometers
const Vector3f &velocity_increase = (accel_ef + accel_correction_ef) * dt;
// calculate new estimate of position
_position_base += (_velocity + velocity_increase*0.5) * dt;
// update the corrected position estimate
_position = _position_base + _position_correction;
// calculate new velocity
_velocity += velocity_increase;
// store 3rd order estimate (i.e. estimated vertical position) for future use
_hist_position_estimate_z.push_back(_position_base.z);
// store 3rd order estimate (i.e. horizontal position) for future use at 10hz
_historic_xy_counter++;
if( _historic_xy_counter >= AP_INTERTIALNAV_SAVE_POS_AFTER_ITERATIONS ) {
_historic_xy_counter = 0;
_hist_position_estimate_x.push_back(_position_base.x);
_hist_position_estimate_y.push_back(_position_base.y);
}
}
//
// XY Axis specific methods
//
// set time constant - set timeconstant used by complementary filter
void AP_InertialNav::set_time_constant_xy( float time_constant_in_seconds )
{
// ensure it's a reasonable value
if( time_constant_in_seconds > 0 && time_constant_in_seconds < 30 ) {
_time_constant_xy = time_constant_in_seconds;
update_gains();
}
}
// position_ok - return true if position has been initialised and have received gps data within 3 seconds
bool AP_InertialNav::position_ok() const
{
return _xy_enabled;
}
// check_gps - check if new gps readings have arrived and use them to correct position estimates
void AP_InertialNav::check_gps()
{
const uint32_t now = hal.scheduler->millis();
// compare gps time to previous reading
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const AP_GPS &gps = _ahrs.get_gps();
if(gps.last_fix_time_ms() != _gps_last_time ) {
// call position correction method
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correct_with_gps(now, gps.location().lng, gps.location().lat);
// record gps time and system time of this update
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_gps_last_time = gps.last_fix_time_ms();
}else{
// if GPS updates stop arriving degrade position error to 10% over 2 seconds (assumes 100hz update rate)
if (now - _gps_last_update > AP_INTERTIALNAV_GPS_TIMEOUT_MS) {
_position_error.x *= 0.9886;
_position_error.y *= 0.9886;
// increment error count
if (_flags.ignore_error == 0 && _error_count < 255 && _xy_enabled) {
_error_count++;
}
}
}
}
// correct_with_gps - modifies accelerometer offsets using gps
void AP_InertialNav::correct_with_gps(uint32_t now, int32_t lon, int32_t lat)
{
float dt,x,y;
float hist_position_base_x, hist_position_base_y;
// calculate time since last gps reading
dt = (float)(now - _gps_last_update) * 0.001f;
// update last gps update time
_gps_last_update = now;
// discard samples where dt is too large
if( dt > 1.0f || dt == 0 || !_xy_enabled) {
return;
}
// calculate distance from base location
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x = (float)(lat - _ahrs.get_home().lat) * LATLON_TO_CM;
y = (float)(lon - _ahrs.get_home().lng) * _lon_to_cm_scaling;
// sanity check the gps position. Relies on the main code calling GPS_Glitch::check_position() immediatley after a GPS update
if (_glitch_detector.glitching()) {
// failed sanity check so degrate position_error to 10% over 2 seconds (assumes 5hz update rate)
_position_error.x *= 0.7943;
_position_error.y *= 0.7943;
}else{
// if our internal glitching flag (from previous iteration) is true we have just recovered from a glitch
// reset the inertial nav position and velocity to gps values
if (_flags.gps_glitching) {
set_position_xy(x,y);
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set_velocity_xy(_ahrs.get_gps().velocity().x * 100.0f,
_ahrs.get_gps().velocity().y * 100.0f);
_position_error.x = 0;
_position_error.y = 0;
}else{
// ublox gps positions are delayed by 400ms
// we store historical position at 10hz so 4 iterations ago
if( _hist_position_estimate_x.is_full()) {
hist_position_base_x = _hist_position_estimate_x.front();
hist_position_base_y = _hist_position_estimate_y.front();
}else{
hist_position_base_x = _position_base.x;
hist_position_base_y = _position_base.y;
}
// calculate error in position from gps with our historical estimate
_position_error.x = x - (hist_position_base_x + _position_correction.x);
_position_error.y = y - (hist_position_base_y + _position_correction.y);
}
}
// update our internal record of glitching flag so that we can notice a change
_flags.gps_glitching = _glitch_detector.glitching();
}
// get accel based latitude
int32_t AP_InertialNav::get_latitude() const
{
// make sure we've been initialised
if( !_xy_enabled ) {
return 0;
}
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return _ahrs.get_home().lat + (int32_t)(_position.x/LATLON_TO_CM);
}
// get accel based longitude
int32_t AP_InertialNav::get_longitude() const
{
// make sure we've been initialised
if( !_xy_enabled ) {
return 0;
}
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return _ahrs.get_home().lng + (int32_t)(_position.y / _lon_to_cm_scaling);
}
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// setup_home_position - reset state for home position change
void AP_InertialNav::setup_home_position(void)
{
// set longitude to meters scaling to offset the shrinking longitude as we go towards the poles
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_lon_to_cm_scaling = longitude_scale(_ahrs.get_home()) * LATLON_TO_CM;
// reset corrections to base position to zero
_position_base.x = 0;
_position_base.y = 0;
_position_correction.x = 0;
_position_correction.y = 0;
_position.x = 0;
_position.y = 0;
// clear historic estimates
_hist_position_estimate_x.clear();
_hist_position_estimate_y.clear();
// set xy as enabled
_xy_enabled = true;
}
// get accel based latitude
float AP_InertialNav::get_latitude_diff() const
{
// make sure we've been initialised
if( !_xy_enabled ) {
return 0;
}
return (_position.x/LATLON_TO_CM);
}
// get accel based longitude
float AP_InertialNav::get_longitude_diff() const
{
// make sure we've been initialised
if( !_xy_enabled ) {
return 0;
}
return (_position.y / _lon_to_cm_scaling);
}
// set_velocity_xy - set velocity in latitude & longitude directions (in cm/s)
void AP_InertialNav::set_velocity_xy(float x, float y)
{
_velocity.x = x;
_velocity.y = y;
}
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// set_velocity_xy - set velocity in latitude & longitude directions (in cm/s)
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float AP_InertialNav::get_velocity_xy() const
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{
return pythagorous2(_velocity.x, _velocity.y);
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}
//
// Z Axis methods
//
// set time constant - set timeconstant used by complementary filter
void AP_InertialNav::set_time_constant_z( float time_constant_in_seconds )
{
// ensure it's a reasonable value
if( time_constant_in_seconds > 0 && time_constant_in_seconds < 30 ) {
_time_constant_z = time_constant_in_seconds;
update_gains();
}
}
// check_baro - check if new baro readings have arrived and use them to correct vertical accelerometer offsets
void AP_InertialNav::check_baro()
{
uint32_t baro_update_time;
// calculate time since last baro reading (in ms)
baro_update_time = _baro.get_last_update();
if( baro_update_time != _baro_last_update ) {
const float dt = (float)(baro_update_time - _baro_last_update) * 0.001f; // in seconds
// call correction method
correct_with_baro(_baro.get_altitude()*100, dt);
_baro_last_update = baro_update_time;
}
}
// correct_with_baro - modifies accelerometer offsets using barometer. dt is time since last baro reading
void AP_InertialNav::correct_with_baro(float baro_alt, float dt)
{
static uint8_t first_reads = 0;
// discard samples where dt is too large
if( dt > 0.5f ) {
return;
}
// discard first 10 reads but perform some initialisation
if( first_reads <= 10 ) {
set_altitude(baro_alt);
first_reads++;
}
// 3rd order samples (i.e. position from baro) are delayed by 150ms (15 iterations at 100hz)
// so we should calculate error using historical estimates
float hist_position_base_z;
if( _hist_position_estimate_z.is_full() ) {
hist_position_base_z = _hist_position_estimate_z.front();
}else{
hist_position_base_z = _position_base.z;
}
// calculate error in position from baro with our estimate
_position_error.z = baro_alt - (hist_position_base_z + _position_correction.z);
}
// set_altitude - set base altitude estimate in cm
void AP_InertialNav::set_altitude( float new_altitude)
{
_position_base.z = new_altitude;
_position_correction.z = 0;
_position.z = new_altitude; // _position = _position_base + _position_correction
}
//
// Private methods
//
// update_gains - update gains from time constant (given in seconds)
void AP_InertialNav::update_gains()
{
// X & Y axis time constant
if( _time_constant_xy == 0 ) {
_k1_xy = _k2_xy = _k3_xy = 0;
}else{
_k1_xy = 3 / _time_constant_xy;
_k2_xy = 3 / (_time_constant_xy*_time_constant_xy);
_k3_xy = 1 / (_time_constant_xy*_time_constant_xy*_time_constant_xy);
}
// Z axis time constant
if( _time_constant_z == 0 ) {
_k1_z = _k2_z = _k3_z = 0;
}else{
_k1_z = 3 / _time_constant_z;
_k2_z = 3 / (_time_constant_z*_time_constant_z);
_k3_z = 1 / (_time_constant_z*_time_constant_z*_time_constant_z);
}
}
// set_velocity_z - get latest climb rate (in cm/s)
void AP_InertialNav::set_velocity_z(float z )
{
_velocity.z = z;
}
// set_position_xy - sets inertial navigation position to given xy coordinates from home
void AP_InertialNav::set_position_xy(float x, float y)
{
// reset position from home
_position_base.x = x;
_position_base.y = y;
_position_correction.x = 0;
_position_correction.y = 0;
// clear historic estimates
_hist_position_estimate_x.clear();
_hist_position_estimate_y.clear();
// add new position for future use
_historic_xy_counter = 0;
_hist_position_estimate_x.push_back(_position_base.x);
_hist_position_estimate_y.push_back(_position_base.y);
}