diff --git a/src/modules/sensors/vehicle_gps_position/CMakeLists.txt b/src/modules/sensors/vehicle_gps_position/CMakeLists.txt index f8665f0360..c3c55e1ab3 100644 --- a/src/modules/sensors/vehicle_gps_position/CMakeLists.txt +++ b/src/modules/sensors/vehicle_gps_position/CMakeLists.txt @@ -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) diff --git a/src/modules/sensors/vehicle_gps_position/gps_blending.cpp b/src/modules/sensors/vehicle_gps_position/gps_blending.cpp index e3f13212dc..86b26a5277 100644 --- a/src/modules/sensors/vehicle_gps_position/gps_blending.cpp +++ b/src/modules/sensors/vehicle_gps_position/gps_blending.cpp @@ -36,555 +36,3 @@ */ #include "gps_blending.hpp" - -#include -#include -#include - -using matrix::Vector2f; -using math::constrain; - -template class GpsBlending<2>; - -template -void GpsBlending::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 -bool GpsBlending::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 -sensor_gps_s GpsBlending::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 -void GpsBlending::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 -void GpsBlending::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; -} diff --git a/src/modules/sensors/vehicle_gps_position/gps_blending.hpp b/src/modules/sensors/vehicle_gps_position/gps_blending.hpp index e713128330..607957f0c0 100644 --- a/src/modules/sensors/vehicle_gps_position/gps_blending.hpp +++ b/src/modules/sensors/vehicle_gps_position/gps_blending.hpp @@ -42,6 +42,13 @@ #include #include +#include +#include +#include + +using matrix::Vector2f; +using math::constrain; + using namespace time_literals; template @@ -129,3 +136,546 @@ private: float _blending_time_constant{0.f}; }; + +template +void GpsBlending::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 +bool GpsBlending::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 +sensor_gps_s GpsBlending::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 +void GpsBlending::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 +void GpsBlending::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; +}