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gps blend: move definition to header file

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bresch 2021-01-28 18:21:09 +01:00 committed by Lorenz Meier
parent 1333664a14
commit 1cde5074ea
3 changed files with 552 additions and 552 deletions
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2
src/modules/sensors/vehicle_gps_position/CMakeLists.txt
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@ -38,3 +38,5 @@ px4_add_library(vehicle_gps_position
gps_blending.hpp
)
target_link_libraries(vehicle_gps_position PRIVATE ecl_geo px4_work_queue)
px4_add_functional_gtest(SRC gps_blending_test.cpp LINKLIBS ecl_geo)

552
src/modules/sensors/vehicle_gps_position/gps_blending.cpp
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@ -36,555 +36,3 @@
*/
#include "gps_blending.hpp"
#include <float.h>
#include <lib/ecl/geo/geo.h>
#include <lib/mathlib/mathlib.h>
using matrix::Vector2f;
using math::constrain;
template class GpsBlending<2>;
template <int GPS_MAX_RECEIVERS>
void GpsBlending<GPS_MAX_RECEIVERS>::update()
{
_is_new_output_data_available = false;
// blend multiple receivers if available
if (!blend_gps_data()) {
// Only use selected receiver data if it has been updated
uint8_t gps_select_index = 0;
// Find the single "best" GPS from the data we have
// First, find the GPS(s) with the best fix
uint8_t best_fix = 0;
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
if (_gps_state[i].fix_type > best_fix) {
best_fix = _gps_state[i].fix_type;
}
}
// Second, compare GPS's with best fix and take the one with most satellites
uint8_t max_sats = 0;
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
if (_gps_state[i].fix_type == best_fix && _gps_state[i].satellites_used > max_sats) {
max_sats = _gps_state[i].satellites_used;
gps_select_index = i;
}
}
// Check for new data on selected GPS, and clear blend offsets
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
_NE_pos_offset_m[i].zero();
_hgt_offset_mm[i] = 0.0f;
}
// re-publish current best GPS
_selected_gps = gps_select_index;
_is_new_output_data_available = _gps_updated[gps_select_index];
}
}
template <int GPS_MAX_RECEIVERS>
bool GpsBlending<GPS_MAX_RECEIVERS>::blend_gps_data()
{
/*
* If both receivers have the same update rate, use the oldest non-zero time.
* If two receivers with different update rates are used, use the slowest.
* If time difference is excessive, use newest to prevent a disconnected receiver
* from blocking updates.
*/
// Calculate the time step for each receiver with some filtering to reduce the effects of jitter
// Find the largest and smallest time step.
float dt_max = 0.0f;
float dt_min = GPS_TIMEOUT_S;
uint8_t gps_count = 0; // Count of receivers which have an active >=2D fix
const hrt_abstime hrt_now = hrt_absolute_time();
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
const float raw_dt = 1e-6f * (float)(_gps_state[i].timestamp - _time_prev_us[i]);
const float present_dt = 1e-6f * (float)(hrt_now - _gps_state[i].timestamp);
if (raw_dt > 0.0f && raw_dt < GPS_TIMEOUT_S) {
_gps_dt[i] = 0.1f * raw_dt + 0.9f * _gps_dt[i];
} else if (present_dt >= GPS_TIMEOUT_S) {
// Timed out - kill the stored fix for this receiver and don't track its (stale) gps_dt
_gps_state[i].timestamp = 0;
_gps_state[i].fix_type = 0;
_gps_state[i].satellites_used = 0;
_gps_state[i].vel_ned_valid = 0;
continue;
}
// Only count GPSs with at least a 2D fix for blending purposes
if (_gps_state[i].fix_type < 2) {
continue;
}
if (_gps_dt[i] > dt_max) {
dt_max = _gps_dt[i];
_gps_slowest_index = i;
}
if (_gps_dt[i] < dt_min) {
dt_min = _gps_dt[i];
}
gps_count++;
}
// Find the receiver that is last be updated
uint64_t max_us = 0; // newest non-zero system time of arrival of a GPS message
uint64_t min_us = -1; // oldest non-zero system time of arrival of a GPS message
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
// Find largest and smallest times
if (_gps_state[i].timestamp > max_us) {
max_us = _gps_state[i].timestamp;
_gps_newest_index = i;
}
if ((_gps_state[i].timestamp < min_us) && (_gps_state[i].timestamp > 0)) {
min_us = _gps_state[i].timestamp;
}
}
if (gps_count < 2) {
// Less than 2 receivers left, so fall out of blending
return false;
}
/*
* If the largest dt is less than 20% greater than the smallest, then we have receivers
* running at the same rate then we wait until we have two messages with an arrival time
* difference that is less than 50% of the smallest time step and use the time stamp from
* the newest data.
* Else we have two receivers at different update rates and use the slowest receiver
* as the timing reference.
*/
bool gps_new_output_data = false;
if ((dt_max - dt_min) < 0.2f * dt_min) {
// both receivers assumed to be running at the same rate
if ((max_us - min_us) < (uint64_t)(5e5f * dt_min)) {
// data arrival within a short time window enables the two measurements to be blended
_gps_time_ref_index = _gps_newest_index;
gps_new_output_data = true;
}
} else {
// both receivers running at different rates
_gps_time_ref_index = _gps_slowest_index;
if (_gps_state[_gps_time_ref_index].timestamp > _time_prev_us[_gps_time_ref_index]) {
// blend data at the rate of the slower receiver
gps_new_output_data = true;
}
}
if (gps_new_output_data) {
// calculate the sum squared speed accuracy across all GPS sensors
float speed_accuracy_sum_sq = 0.0f;
if (_blend_use_spd_acc) {
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
if (_gps_state[i].fix_type >= 3 && _gps_state[i].s_variance_m_s > 0.0f) {
speed_accuracy_sum_sq += _gps_state[i].s_variance_m_s * _gps_state[i].s_variance_m_s;
}
}
}
// calculate the sum squared horizontal position accuracy across all GPS sensors
float horizontal_accuracy_sum_sq = 0.0f;
if (_blend_use_hpos_acc) {
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
if (_gps_state[i].fix_type >= 2 && _gps_state[i].eph > 0.0f) {
horizontal_accuracy_sum_sq += _gps_state[i].eph * _gps_state[i].eph;
}
}
}
// calculate the sum squared vertical position accuracy across all GPS sensors
float vertical_accuracy_sum_sq = 0.0f;
if (_blend_use_vpos_acc) {
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
if (_gps_state[i].fix_type >= 3 && _gps_state[i].epv > 0.0f) {
vertical_accuracy_sum_sq += _gps_state[i].epv * _gps_state[i].epv;
}
}
}
// Check if we can do blending using reported accuracy
bool can_do_blending = (horizontal_accuracy_sum_sq > 0.0f || vertical_accuracy_sum_sq > 0.0f
|| speed_accuracy_sum_sq > 0.0f);
// if we can't do blending using reported accuracy, return false and hard switch logic will be used instead
if (!can_do_blending) {
return false;
}
float sum_of_all_weights = 0.0f;
// calculate a weighting using the reported speed accuracy
float spd_blend_weights[GPS_MAX_RECEIVERS] {};
if (speed_accuracy_sum_sq > 0.0f && _blend_use_spd_acc) {
// calculate the weights using the inverse of the variances
float sum_of_spd_weights = 0.0f;
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
if (_gps_state[i].fix_type >= 3 && _gps_state[i].s_variance_m_s >= 0.001f) {
spd_blend_weights[i] = 1.0f / (_gps_state[i].s_variance_m_s * _gps_state[i].s_variance_m_s);
sum_of_spd_weights += spd_blend_weights[i];
}
}
// normalise the weights
if (sum_of_spd_weights > 0.0f) {
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
spd_blend_weights[i] = spd_blend_weights[i] / sum_of_spd_weights;
}
sum_of_all_weights += 1.0f;
}
}
// calculate a weighting using the reported horizontal position
float hpos_blend_weights[GPS_MAX_RECEIVERS] {};
if (horizontal_accuracy_sum_sq > 0.0f && _blend_use_hpos_acc) {
// calculate the weights using the inverse of the variances
float sum_of_hpos_weights = 0.0f;
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
if (_gps_state[i].fix_type >= 2 && _gps_state[i].eph >= 0.001f) {
hpos_blend_weights[i] = horizontal_accuracy_sum_sq / (_gps_state[i].eph * _gps_state[i].eph);
sum_of_hpos_weights += hpos_blend_weights[i];
}
}
// normalise the weights
if (sum_of_hpos_weights > 0.0f) {
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
hpos_blend_weights[i] = hpos_blend_weights[i] / sum_of_hpos_weights;
}
sum_of_all_weights += 1.0f;
}
}
// calculate a weighting using the reported vertical position accuracy
float vpos_blend_weights[GPS_MAX_RECEIVERS] = {};
if (vertical_accuracy_sum_sq > 0.0f && _blend_use_vpos_acc) {
// calculate the weights using the inverse of the variances
float sum_of_vpos_weights = 0.0f;
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
if (_gps_state[i].fix_type >= 3 && _gps_state[i].epv >= 0.001f) {
vpos_blend_weights[i] = vertical_accuracy_sum_sq / (_gps_state[i].epv * _gps_state[i].epv);
sum_of_vpos_weights += vpos_blend_weights[i];
}
}
// normalise the weights
if (sum_of_vpos_weights > 0.0f) {
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
vpos_blend_weights[i] = vpos_blend_weights[i] / sum_of_vpos_weights;
}
sum_of_all_weights += 1.0f;
};
}
// blend weight for each GPS. The blend weights must sum to 1.0 across all instances.
float blend_weights[GPS_MAX_RECEIVERS];
// calculate an overall weight
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
blend_weights[i] = (hpos_blend_weights[i] + vpos_blend_weights[i] + spd_blend_weights[i]) / sum_of_all_weights;
}
// With updated weights we can calculate a blended GPS solution and
// offsets for each physical receiver
sensor_gps_s gps_blended_state = gps_blend_states(blend_weights);
update_gps_offsets(gps_blended_state);
// calculate a blended output from the offset corrected receiver data
// publish if blending was successful
calc_gps_blend_output(gps_blended_state, blend_weights);
_gps_blended_state = gps_blended_state;
_selected_gps = GPS_MAX_RECEIVERS;
_is_new_output_data_available = true;
}
return true;
}
template <int GPS_MAX_RECEIVERS>
sensor_gps_s GpsBlending<GPS_MAX_RECEIVERS>::gps_blend_states(float blend_weights[GPS_MAX_RECEIVERS]) const
{
// initialise the blended states so we can accumulate the results using the weightings for each GPS receiver.
sensor_gps_s gps_blended_state{};
gps_blended_state.eph = FLT_MAX;
gps_blended_state.epv = FLT_MAX;
gps_blended_state.s_variance_m_s = FLT_MAX;
gps_blended_state.vel_ned_valid = true;
gps_blended_state.hdop = FLT_MAX;
gps_blended_state.vdop = FLT_MAX;
// combine the the GPS states into a blended solution using the weights calculated in calc_blend_weights()
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
// blend the timing data
gps_blended_state.timestamp += (uint64_t)((double)_gps_state[i].timestamp * (double)blend_weights[i]);
// use the highest status
if (_gps_state[i].fix_type > gps_blended_state.fix_type) {
gps_blended_state.fix_type = _gps_state[i].fix_type;
}
// Assume blended error magnitude, DOP and sat count is equal to the best value from contributing receivers
// If any receiver contributing has an invalid velocity, then report blended velocity as invalid
if (blend_weights[i] > 0.0f) {
// calculate a blended average speed and velocity vector
gps_blended_state.vel_m_s += _gps_state[i].vel_m_s * blend_weights[i];
gps_blended_state.vel_n_m_s += _gps_state[i].vel_n_m_s * blend_weights[i];
gps_blended_state.vel_e_m_s += _gps_state[i].vel_e_m_s * blend_weights[i];
gps_blended_state.vel_d_m_s += _gps_state[i].vel_d_m_s * blend_weights[i];
if (_gps_state[i].eph > 0.0f
&& _gps_state[i].eph < gps_blended_state.eph) {
gps_blended_state.eph = _gps_state[i].eph;
}
if (_gps_state[i].epv > 0.0f
&& _gps_state[i].epv < gps_blended_state.epv) {
gps_blended_state.epv = _gps_state[i].epv;
}
if (_gps_state[i].s_variance_m_s > 0.0f
&& _gps_state[i].s_variance_m_s < gps_blended_state.s_variance_m_s) {
gps_blended_state.s_variance_m_s = _gps_state[i].s_variance_m_s;
}
if (_gps_state[i].hdop > 0
&& _gps_state[i].hdop < gps_blended_state.hdop) {
gps_blended_state.hdop = _gps_state[i].hdop;
}
if (_gps_state[i].vdop > 0
&& _gps_state[i].vdop < gps_blended_state.vdop) {
gps_blended_state.vdop = _gps_state[i].vdop;
}
if (_gps_state[i].satellites_used > 0
&& _gps_state[i].satellites_used > gps_blended_state.satellites_used) {
gps_blended_state.satellites_used = _gps_state[i].satellites_used;
}
if (!_gps_state[i].vel_ned_valid) {
gps_blended_state.vel_ned_valid = false;
}
}
// TODO read parameters for individual GPS antenna positions and blend
// Vector3f temp_antenna_offset = _antenna_offset[i];
// temp_antenna_offset *= blend_weights[i];
// _blended_antenna_offset += temp_antenna_offset;
}
/*
* Calculate the instantaneous weighted average location using available GPS instances and store in _gps_state.
* This is statistically the most likely location, but may not be stable enough for direct use by the EKF.
*/
// Use the GPS with the highest weighting as the reference position
float best_weight = 0.0f;
// index of the physical receiver with the lowest reported error
uint8_t gps_best_index = 0;
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
if (blend_weights[i] > best_weight) {
best_weight = blend_weights[i];
gps_best_index = i;
gps_blended_state.lat = _gps_state[i].lat;
gps_blended_state.lon = _gps_state[i].lon;
gps_blended_state.alt = _gps_state[i].alt;
}
}
// Convert each GPS position to a local NEU offset relative to the reference position
Vector2f blended_NE_offset_m{0, 0};
float blended_alt_offset_mm = 0.0f;
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
if ((blend_weights[i] > 0.0f) && (i != gps_best_index)) {
// calculate the horizontal offset
Vector2f horiz_offset{};
get_vector_to_next_waypoint((gps_blended_state.lat / 1.0e7), (gps_blended_state.lon / 1.0e7),
(_gps_state[i].lat / 1.0e7), (_gps_state[i].lon / 1.0e7),
&horiz_offset(0), &horiz_offset(1));
// sum weighted offsets
blended_NE_offset_m += horiz_offset * blend_weights[i];
// calculate vertical offset
float vert_offset = (float)(_gps_state[i].alt - gps_blended_state.alt);
// sum weighted offsets
blended_alt_offset_mm += vert_offset * blend_weights[i];
}
}
// Add the sum of weighted offsets to the reference position to obtain the blended position
const double lat_deg_now = (double)gps_blended_state.lat * 1.0e-7;
const double lon_deg_now = (double)gps_blended_state.lon * 1.0e-7;
double lat_deg_res = 0;
double lon_deg_res = 0;
add_vector_to_global_position(lat_deg_now, lon_deg_now,
blended_NE_offset_m(0), blended_NE_offset_m(1),
&lat_deg_res, &lon_deg_res);
gps_blended_state.lat = (int32_t)(1.0E7 * lat_deg_res);
gps_blended_state.lon = (int32_t)(1.0E7 * lon_deg_res);
gps_blended_state.alt += (int32_t)blended_alt_offset_mm;
// Take GPS heading from the highest weighted receiver that is publishing a valid .heading value
uint8_t gps_best_yaw_index = 0;
float best_yaw_weight = 0.0f;
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
if (PX4_ISFINITE(_gps_state[i].heading) && (blend_weights[i] > best_yaw_weight)) {
best_yaw_weight = blend_weights[i];
gps_best_yaw_index = i;
}
}
gps_blended_state.heading = _gps_state[gps_best_yaw_index].heading;
gps_blended_state.heading_offset = _gps_state[gps_best_yaw_index].heading_offset;
return gps_blended_state;
}
template <int GPS_MAX_RECEIVERS>
void GpsBlending<GPS_MAX_RECEIVERS>::update_gps_offsets(const sensor_gps_s &gps_blended_state)
{
// Calculate filter coefficients to be applied to the offsets for each GPS position and height offset
// A weighting of 1 will make the offset adjust the slowest, a weighting of 0 will make it adjust with zero filtering
float alpha[GPS_MAX_RECEIVERS] {};
float omega_lpf = 1.0f / fmaxf(_blending_time_constant, 1.0f);
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
if (_gps_state[i].timestamp - _time_prev_us[i] > 0) {
// calculate the filter coefficient that achieves the time constant specified by the user adjustable parameter
alpha[i] = constrain(omega_lpf * 1e-6f * (float)(_gps_state[i].timestamp - _time_prev_us[i]),
0.0f, 1.0f);
_time_prev_us[i] = _gps_state[i].timestamp;
}
}
// Calculate a filtered position delta for each GPS relative to the blended solution state
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
Vector2f offset;
get_vector_to_next_waypoint((_gps_state[i].lat / 1.0e7), (_gps_state[i].lon / 1.0e7),
(gps_blended_state.lat / 1.0e7), (gps_blended_state.lon / 1.0e7),
&offset(0), &offset(1));
_NE_pos_offset_m[i] = offset * alpha[i] + _NE_pos_offset_m[i] * (1.0f - alpha[i]);
_hgt_offset_mm[i] = (float)(gps_blended_state.alt - _gps_state[i].alt) * alpha[i] +
_hgt_offset_mm[i] * (1.0f - alpha[i]);
}
// calculate offset limits from the largest difference between receivers
Vector2f max_ne_offset{};
float max_alt_offset = 0;
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
for (uint8_t j = i; j < GPS_MAX_RECEIVERS; j++) {
if (i != j) {
Vector2f offset;
get_vector_to_next_waypoint((_gps_state[i].lat / 1.0e7), (_gps_state[i].lon / 1.0e7),
(_gps_state[j].lat / 1.0e7), (_gps_state[j].lon / 1.0e7),
&offset(0), &offset(1));
max_ne_offset(0) = fmaxf(max_ne_offset(0), fabsf(offset(0)));
max_ne_offset(1) = fmaxf(max_ne_offset(1), fabsf(offset(1)));
max_alt_offset = fmaxf(max_alt_offset, fabsf((float)(_gps_state[i].alt - _gps_state[j].alt)));
}
}
}
// apply offset limits
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
_NE_pos_offset_m[i](0) = constrain(_NE_pos_offset_m[i](0), -max_ne_offset(0), max_ne_offset(0));
_NE_pos_offset_m[i](1) = constrain(_NE_pos_offset_m[i](1), -max_ne_offset(1), max_ne_offset(1));
_hgt_offset_mm[i] = constrain(_hgt_offset_mm[i], -max_alt_offset, max_alt_offset);
}
}
template <int GPS_MAX_RECEIVERS>
void GpsBlending<GPS_MAX_RECEIVERS>::calc_gps_blend_output(sensor_gps_s &gps_blended_state,
float blend_weights[GPS_MAX_RECEIVERS]) const
{
// Convert each GPS position to a local NEU offset relative to the reference position
// which is defined as the positon of the blended solution calculated from non offset corrected data
Vector2f blended_NE_offset_m{0, 0};
float blended_alt_offset_mm = 0.0f;
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
if (blend_weights[i] > 0.0f) {
// Add the sum of weighted offsets to the reference position to obtain the blended position
const double lat_deg_orig = (double)_gps_state[i].lat * 1.0e-7;
const double lon_deg_orig = (double)_gps_state[i].lon * 1.0e-7;
double lat_deg_offset_res = 0;
double lon_deg_offset_res = 0;
add_vector_to_global_position(lat_deg_orig, lon_deg_orig,
_NE_pos_offset_m[i](0), _NE_pos_offset_m[i](1),
&lat_deg_offset_res, &lon_deg_offset_res);
float alt_offset = _gps_state[i].alt + (int32_t)_hgt_offset_mm[i];
// calculate the horizontal offset
Vector2f horiz_offset{};
get_vector_to_next_waypoint((gps_blended_state.lat / 1.0e7), (gps_blended_state.lon / 1.0e7),
lat_deg_offset_res, lon_deg_offset_res,
&horiz_offset(0), &horiz_offset(1));
// sum weighted offsets
blended_NE_offset_m += horiz_offset * blend_weights[i];
// calculate vertical offset
float vert_offset = alt_offset - gps_blended_state.alt;
// sum weighted offsets
blended_alt_offset_mm += vert_offset * blend_weights[i];
}
}
// Add the sum of weighted offsets to the reference position to obtain the blended position
const double lat_deg_now = (double)gps_blended_state.lat * 1.0e-7;
const double lon_deg_now = (double)gps_blended_state.lon * 1.0e-7;
double lat_deg_res = 0;
double lon_deg_res = 0;
add_vector_to_global_position(lat_deg_now, lon_deg_now,
blended_NE_offset_m(0), blended_NE_offset_m(1),
&lat_deg_res, &lon_deg_res);
gps_blended_state.lat = (int32_t)(1.0E7 * lat_deg_res);
gps_blended_state.lon = (int32_t)(1.0E7 * lon_deg_res);
gps_blended_state.alt = gps_blended_state.alt + (int32_t)blended_alt_offset_mm;
}

550
src/modules/sensors/vehicle_gps_position/gps_blending.hpp
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@ -42,6 +42,13 @@
#include <px4_platform_common/defines.h>
#include <uORB/topics/sensor_gps.h>
#include <float.h>
#include <lib/ecl/geo/geo.h>
#include <lib/mathlib/mathlib.h>
using matrix::Vector2f;
using math::constrain;
using namespace time_literals;
template<int GPS_MAX_RECEIVERS>
@ -129,3 +136,546 @@ private:
float _blending_time_constant{0.f};
};
template <int GPS_MAX_RECEIVERS>
void GpsBlending<GPS_MAX_RECEIVERS>::update()
{
_is_new_output_data_available = false;
// blend multiple receivers if available
if (!blend_gps_data()) {
// Only use selected receiver data if it has been updated
uint8_t gps_select_index = 0;
// Find the single "best" GPS from the data we have
// First, find the GPS(s) with the best fix
uint8_t best_fix = 0;
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
if (_gps_state[i].fix_type > best_fix) {
best_fix = _gps_state[i].fix_type;
}
}
// Second, compare GPS's with best fix and take the one with most satellites
uint8_t max_sats = 0;
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
if (_gps_state[i].fix_type == best_fix && _gps_state[i].satellites_used > max_sats) {
max_sats = _gps_state[i].satellites_used;
gps_select_index = i;
}
}
// Check for new data on selected GPS, and clear blend offsets
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
_NE_pos_offset_m[i].zero();
_hgt_offset_mm[i] = 0.0f;
}
// re-publish current best GPS
_selected_gps = gps_select_index;
_is_new_output_data_available = _gps_updated[gps_select_index];
}
}
template <int GPS_MAX_RECEIVERS>
bool GpsBlending<GPS_MAX_RECEIVERS>::blend_gps_data()
{
/*
* If both receivers have the same update rate, use the oldest non-zero time.
* If two receivers with different update rates are used, use the slowest.
* If time difference is excessive, use newest to prevent a disconnected receiver
* from blocking updates.
*/
// Calculate the time step for each receiver with some filtering to reduce the effects of jitter
// Find the largest and smallest time step.
float dt_max = 0.0f;
float dt_min = GPS_TIMEOUT_S;
uint8_t gps_count = 0; // Count of receivers which have an active >=2D fix
const hrt_abstime hrt_now = hrt_absolute_time();
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
const float raw_dt = 1e-6f * (float)(_gps_state[i].timestamp - _time_prev_us[i]);
const float present_dt = 1e-6f * (float)(hrt_now - _gps_state[i].timestamp);
if (raw_dt > 0.0f && raw_dt < GPS_TIMEOUT_S) {
_gps_dt[i] = 0.1f * raw_dt + 0.9f * _gps_dt[i];
} else if (present_dt >= GPS_TIMEOUT_S) {
// Timed out - kill the stored fix for this receiver and don't track its (stale) gps_dt
_gps_state[i].timestamp = 0;
_gps_state[i].fix_type = 0;
_gps_state[i].satellites_used = 0;
_gps_state[i].vel_ned_valid = 0;
continue;
}
// Only count GPSs with at least a 2D fix for blending purposes
if (_gps_state[i].fix_type < 2) {
continue;
}
if (_gps_dt[i] > dt_max) {
dt_max = _gps_dt[i];
_gps_slowest_index = i;
}
if (_gps_dt[i] < dt_min) {
dt_min = _gps_dt[i];
}
gps_count++;
}
// Find the receiver that is last be updated
uint64_t max_us = 0; // newest non-zero system time of arrival of a GPS message
uint64_t min_us = -1; // oldest non-zero system time of arrival of a GPS message
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
// Find largest and smallest times
if (_gps_state[i].timestamp > max_us) {
max_us = _gps_state[i].timestamp;
_gps_newest_index = i;
}
if ((_gps_state[i].timestamp < min_us) && (_gps_state[i].timestamp > 0)) {
min_us = _gps_state[i].timestamp;
}
}
if (gps_count < 2) {
// Less than 2 receivers left, so fall out of blending
return false;
}
/*
* If the largest dt is less than 20% greater than the smallest, then we have receivers
* running at the same rate then we wait until we have two messages with an arrival time
* difference that is less than 50% of the smallest time step and use the time stamp from
* the newest data.
* Else we have two receivers at different update rates and use the slowest receiver
* as the timing reference.
*/
bool gps_new_output_data = false;
if ((dt_max - dt_min) < 0.2f * dt_min) {
// both receivers assumed to be running at the same rate
if ((max_us - min_us) < (uint64_t)(5e5f * dt_min)) {
// data arrival within a short time window enables the two measurements to be blended
_gps_time_ref_index = _gps_newest_index;
gps_new_output_data = true;
}
} else {
// both receivers running at different rates
_gps_time_ref_index = _gps_slowest_index;
if (_gps_state[_gps_time_ref_index].timestamp > _time_prev_us[_gps_time_ref_index]) {
// blend data at the rate of the slower receiver
gps_new_output_data = true;
}
}
if (gps_new_output_data) {
// calculate the sum squared speed accuracy across all GPS sensors
float speed_accuracy_sum_sq = 0.0f;
if (_blend_use_spd_acc) {
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
if (_gps_state[i].fix_type >= 3 && _gps_state[i].s_variance_m_s > 0.0f) {
speed_accuracy_sum_sq += _gps_state[i].s_variance_m_s * _gps_state[i].s_variance_m_s;
}
}
}
// calculate the sum squared horizontal position accuracy across all GPS sensors
float horizontal_accuracy_sum_sq = 0.0f;
if (_blend_use_hpos_acc) {
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
if (_gps_state[i].fix_type >= 2 && _gps_state[i].eph > 0.0f) {
horizontal_accuracy_sum_sq += _gps_state[i].eph * _gps_state[i].eph;
}
}
}
// calculate the sum squared vertical position accuracy across all GPS sensors
float vertical_accuracy_sum_sq = 0.0f;
if (_blend_use_vpos_acc) {
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
if (_gps_state[i].fix_type >= 3 && _gps_state[i].epv > 0.0f) {
vertical_accuracy_sum_sq += _gps_state[i].epv * _gps_state[i].epv;
}
}
}
// Check if we can do blending using reported accuracy
bool can_do_blending = (horizontal_accuracy_sum_sq > 0.0f || vertical_accuracy_sum_sq > 0.0f
|| speed_accuracy_sum_sq > 0.0f);
// if we can't do blending using reported accuracy, return false and hard switch logic will be used instead
if (!can_do_blending) {
return false;
}
float sum_of_all_weights = 0.0f;
// calculate a weighting using the reported speed accuracy
float spd_blend_weights[GPS_MAX_RECEIVERS] {};
if (speed_accuracy_sum_sq > 0.0f && _blend_use_spd_acc) {
// calculate the weights using the inverse of the variances
float sum_of_spd_weights = 0.0f;
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
if (_gps_state[i].fix_type >= 3 && _gps_state[i].s_variance_m_s >= 0.001f) {
spd_blend_weights[i] = 1.0f / (_gps_state[i].s_variance_m_s * _gps_state[i].s_variance_m_s);
sum_of_spd_weights += spd_blend_weights[i];
}
}
// normalise the weights
if (sum_of_spd_weights > 0.0f) {
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
spd_blend_weights[i] = spd_blend_weights[i] / sum_of_spd_weights;
}
sum_of_all_weights += 1.0f;
}
}
// calculate a weighting using the reported horizontal position
float hpos_blend_weights[GPS_MAX_RECEIVERS] {};
if (horizontal_accuracy_sum_sq > 0.0f && _blend_use_hpos_acc) {
// calculate the weights using the inverse of the variances
float sum_of_hpos_weights = 0.0f;
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
if (_gps_state[i].fix_type >= 2 && _gps_state[i].eph >= 0.001f) {
hpos_blend_weights[i] = horizontal_accuracy_sum_sq / (_gps_state[i].eph * _gps_state[i].eph);
sum_of_hpos_weights += hpos_blend_weights[i];
}
}
// normalise the weights
if (sum_of_hpos_weights > 0.0f) {
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
hpos_blend_weights[i] = hpos_blend_weights[i] / sum_of_hpos_weights;
}
sum_of_all_weights += 1.0f;
}
}
// calculate a weighting using the reported vertical position accuracy
float vpos_blend_weights[GPS_MAX_RECEIVERS] = {};
if (vertical_accuracy_sum_sq > 0.0f && _blend_use_vpos_acc) {
// calculate the weights using the inverse of the variances
float sum_of_vpos_weights = 0.0f;
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
if (_gps_state[i].fix_type >= 3 && _gps_state[i].epv >= 0.001f) {
vpos_blend_weights[i] = vertical_accuracy_sum_sq / (_gps_state[i].epv * _gps_state[i].epv);
sum_of_vpos_weights += vpos_blend_weights[i];
}
}
// normalise the weights
if (sum_of_vpos_weights > 0.0f) {
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
vpos_blend_weights[i] = vpos_blend_weights[i] / sum_of_vpos_weights;
}
sum_of_all_weights += 1.0f;
};
}
// blend weight for each GPS. The blend weights must sum to 1.0 across all instances.
float blend_weights[GPS_MAX_RECEIVERS];
// calculate an overall weight
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
blend_weights[i] = (hpos_blend_weights[i] + vpos_blend_weights[i] + spd_blend_weights[i]) / sum_of_all_weights;
}
// With updated weights we can calculate a blended GPS solution and
// offsets for each physical receiver
sensor_gps_s gps_blended_state = gps_blend_states(blend_weights);
update_gps_offsets(gps_blended_state);
// calculate a blended output from the offset corrected receiver data
// publish if blending was successful
calc_gps_blend_output(gps_blended_state, blend_weights);
_gps_blended_state = gps_blended_state;
_selected_gps = GPS_MAX_RECEIVERS;
_is_new_output_data_available = true;
}
return true;
}
template <int GPS_MAX_RECEIVERS>
sensor_gps_s GpsBlending<GPS_MAX_RECEIVERS>::gps_blend_states(float blend_weights[GPS_MAX_RECEIVERS]) const
{
// initialise the blended states so we can accumulate the results using the weightings for each GPS receiver.
sensor_gps_s gps_blended_state{};
gps_blended_state.eph = FLT_MAX;
gps_blended_state.epv = FLT_MAX;
gps_blended_state.s_variance_m_s = FLT_MAX;
gps_blended_state.vel_ned_valid = true;
gps_blended_state.hdop = FLT_MAX;
gps_blended_state.vdop = FLT_MAX;
// combine the the GPS states into a blended solution using the weights calculated in calc_blend_weights()
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
// blend the timing data
gps_blended_state.timestamp += (uint64_t)((double)_gps_state[i].timestamp * (double)blend_weights[i]);
// use the highest status
if (_gps_state[i].fix_type > gps_blended_state.fix_type) {
gps_blended_state.fix_type = _gps_state[i].fix_type;
}
// Assume blended error magnitude, DOP and sat count is equal to the best value from contributing receivers
// If any receiver contributing has an invalid velocity, then report blended velocity as invalid
if (blend_weights[i] > 0.0f) {
// calculate a blended average speed and velocity vector
gps_blended_state.vel_m_s += _gps_state[i].vel_m_s * blend_weights[i];
gps_blended_state.vel_n_m_s += _gps_state[i].vel_n_m_s * blend_weights[i];
gps_blended_state.vel_e_m_s += _gps_state[i].vel_e_m_s * blend_weights[i];
gps_blended_state.vel_d_m_s += _gps_state[i].vel_d_m_s * blend_weights[i];
if (_gps_state[i].eph > 0.0f
&& _gps_state[i].eph < gps_blended_state.eph) {
gps_blended_state.eph = _gps_state[i].eph;
}
if (_gps_state[i].epv > 0.0f
&& _gps_state[i].epv < gps_blended_state.epv) {
gps_blended_state.epv = _gps_state[i].epv;
}
if (_gps_state[i].s_variance_m_s > 0.0f
&& _gps_state[i].s_variance_m_s < gps_blended_state.s_variance_m_s) {
gps_blended_state.s_variance_m_s = _gps_state[i].s_variance_m_s;
}
if (_gps_state[i].hdop > 0
&& _gps_state[i].hdop < gps_blended_state.hdop) {
gps_blended_state.hdop = _gps_state[i].hdop;
}
if (_gps_state[i].vdop > 0
&& _gps_state[i].vdop < gps_blended_state.vdop) {
gps_blended_state.vdop = _gps_state[i].vdop;
}
if (_gps_state[i].satellites_used > 0
&& _gps_state[i].satellites_used > gps_blended_state.satellites_used) {
gps_blended_state.satellites_used = _gps_state[i].satellites_used;
}
if (!_gps_state[i].vel_ned_valid) {
gps_blended_state.vel_ned_valid = false;
}
}
// TODO read parameters for individual GPS antenna positions and blend
// Vector3f temp_antenna_offset = _antenna_offset[i];
// temp_antenna_offset *= blend_weights[i];
// _blended_antenna_offset += temp_antenna_offset;
}
/*
* Calculate the instantaneous weighted average location using available GPS instances and store in _gps_state.
* This is statistically the most likely location, but may not be stable enough for direct use by the EKF.
*/
// Use the GPS with the highest weighting as the reference position
float best_weight = 0.0f;
// index of the physical receiver with the lowest reported error
uint8_t gps_best_index = 0;
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
if (blend_weights[i] > best_weight) {
best_weight = blend_weights[i];
gps_best_index = i;
gps_blended_state.lat = _gps_state[i].lat;
gps_blended_state.lon = _gps_state[i].lon;
gps_blended_state.alt = _gps_state[i].alt;
}
}
// Convert each GPS position to a local NEU offset relative to the reference position
Vector2f blended_NE_offset_m{0, 0};
float blended_alt_offset_mm = 0.0f;
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
if ((blend_weights[i] > 0.0f) && (i != gps_best_index)) {
// calculate the horizontal offset
Vector2f horiz_offset{};
get_vector_to_next_waypoint((gps_blended_state.lat / 1.0e7), (gps_blended_state.lon / 1.0e7),
(_gps_state[i].lat / 1.0e7), (_gps_state[i].lon / 1.0e7),
&horiz_offset(0), &horiz_offset(1));
// sum weighted offsets
blended_NE_offset_m += horiz_offset * blend_weights[i];
// calculate vertical offset
float vert_offset = (float)(_gps_state[i].alt - gps_blended_state.alt);
// sum weighted offsets
blended_alt_offset_mm += vert_offset * blend_weights[i];
}
}
// Add the sum of weighted offsets to the reference position to obtain the blended position
const double lat_deg_now = (double)gps_blended_state.lat * 1.0e-7;
const double lon_deg_now = (double)gps_blended_state.lon * 1.0e-7;
double lat_deg_res = 0;
double lon_deg_res = 0;
add_vector_to_global_position(lat_deg_now, lon_deg_now,
blended_NE_offset_m(0), blended_NE_offset_m(1),
&lat_deg_res, &lon_deg_res);
gps_blended_state.lat = (int32_t)(1.0E7 * lat_deg_res);
gps_blended_state.lon = (int32_t)(1.0E7 * lon_deg_res);
gps_blended_state.alt += (int32_t)blended_alt_offset_mm;
// Take GPS heading from the highest weighted receiver that is publishing a valid .heading value
uint8_t gps_best_yaw_index = 0;
float best_yaw_weight = 0.0f;
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
if (PX4_ISFINITE(_gps_state[i].heading) && (blend_weights[i] > best_yaw_weight)) {
best_yaw_weight = blend_weights[i];
gps_best_yaw_index = i;
}
}
gps_blended_state.heading = _gps_state[gps_best_yaw_index].heading;
gps_blended_state.heading_offset = _gps_state[gps_best_yaw_index].heading_offset;
return gps_blended_state;
}
template <int GPS_MAX_RECEIVERS>
void GpsBlending<GPS_MAX_RECEIVERS>::update_gps_offsets(const sensor_gps_s &gps_blended_state)
{
// Calculate filter coefficients to be applied to the offsets for each GPS position and height offset
// A weighting of 1 will make the offset adjust the slowest, a weighting of 0 will make it adjust with zero filtering
float alpha[GPS_MAX_RECEIVERS] {};
float omega_lpf = 1.0f / fmaxf(_blending_time_constant, 1.0f);
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
if (_gps_state[i].timestamp - _time_prev_us[i] > 0) {
// calculate the filter coefficient that achieves the time constant specified by the user adjustable parameter
alpha[i] = constrain(omega_lpf * 1e-6f * (float)(_gps_state[i].timestamp - _time_prev_us[i]),
0.0f, 1.0f);
_time_prev_us[i] = _gps_state[i].timestamp;
}
}
// Calculate a filtered position delta for each GPS relative to the blended solution state
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
Vector2f offset;
get_vector_to_next_waypoint((_gps_state[i].lat / 1.0e7), (_gps_state[i].lon / 1.0e7),
(gps_blended_state.lat / 1.0e7), (gps_blended_state.lon / 1.0e7),
&offset(0), &offset(1));
_NE_pos_offset_m[i] = offset * alpha[i] + _NE_pos_offset_m[i] * (1.0f - alpha[i]);
_hgt_offset_mm[i] = (float)(gps_blended_state.alt - _gps_state[i].alt) * alpha[i] +
_hgt_offset_mm[i] * (1.0f - alpha[i]);
}
// calculate offset limits from the largest difference between receivers
Vector2f max_ne_offset{};
float max_alt_offset = 0;
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
for (uint8_t j = i; j < GPS_MAX_RECEIVERS; j++) {
if (i != j) {
Vector2f offset;
get_vector_to_next_waypoint((_gps_state[i].lat / 1.0e7), (_gps_state[i].lon / 1.0e7),
(_gps_state[j].lat / 1.0e7), (_gps_state[j].lon / 1.0e7),
&offset(0), &offset(1));
max_ne_offset(0) = fmaxf(max_ne_offset(0), fabsf(offset(0)));
max_ne_offset(1) = fmaxf(max_ne_offset(1), fabsf(offset(1)));
max_alt_offset = fmaxf(max_alt_offset, fabsf((float)(_gps_state[i].alt - _gps_state[j].alt)));
}
}
}
// apply offset limits
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
_NE_pos_offset_m[i](0) = constrain(_NE_pos_offset_m[i](0), -max_ne_offset(0), max_ne_offset(0));
_NE_pos_offset_m[i](1) = constrain(_NE_pos_offset_m[i](1), -max_ne_offset(1), max_ne_offset(1));
_hgt_offset_mm[i] = constrain(_hgt_offset_mm[i], -max_alt_offset, max_alt_offset);
}
}
template <int GPS_MAX_RECEIVERS>
void GpsBlending<GPS_MAX_RECEIVERS>::calc_gps_blend_output(sensor_gps_s &gps_blended_state,
float blend_weights[GPS_MAX_RECEIVERS]) const
{
// Convert each GPS position to a local NEU offset relative to the reference position
// which is defined as the positon of the blended solution calculated from non offset corrected data
Vector2f blended_NE_offset_m{0, 0};
float blended_alt_offset_mm = 0.0f;
for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
if (blend_weights[i] > 0.0f) {
// Add the sum of weighted offsets to the reference position to obtain the blended position
const double lat_deg_orig = (double)_gps_state[i].lat * 1.0e-7;
const double lon_deg_orig = (double)_gps_state[i].lon * 1.0e-7;
double lat_deg_offset_res = 0;
double lon_deg_offset_res = 0;
add_vector_to_global_position(lat_deg_orig, lon_deg_orig,
_NE_pos_offset_m[i](0), _NE_pos_offset_m[i](1),
&lat_deg_offset_res, &lon_deg_offset_res);
float alt_offset = _gps_state[i].alt + (int32_t)_hgt_offset_mm[i];
// calculate the horizontal offset
Vector2f horiz_offset{};
get_vector_to_next_waypoint((gps_blended_state.lat / 1.0e7), (gps_blended_state.lon / 1.0e7),
lat_deg_offset_res, lon_deg_offset_res,
&horiz_offset(0), &horiz_offset(1));
// sum weighted offsets
blended_NE_offset_m += horiz_offset * blend_weights[i];
// calculate vertical offset
float vert_offset = alt_offset - gps_blended_state.alt;
// sum weighted offsets
blended_alt_offset_mm += vert_offset * blend_weights[i];
}
}
// Add the sum of weighted offsets to the reference position to obtain the blended position
const double lat_deg_now = (double)gps_blended_state.lat * 1.0e-7;
const double lon_deg_now = (double)gps_blended_state.lon * 1.0e-7;
double lat_deg_res = 0;
double lon_deg_res = 0;
add_vector_to_global_position(lat_deg_now, lon_deg_now,
blended_NE_offset_m(0), blended_NE_offset_m(1),
&lat_deg_res, &lon_deg_res);
gps_blended_state.lat = (int32_t)(1.0E7 * lat_deg_res);
gps_blended_state.lon = (int32_t)(1.0E7 * lon_deg_res);
gps_blended_state.alt = gps_blended_state.alt + (int32_t)blended_alt_offset_mm;
}