/**************************************************************************** * * Copyright (c) 2013 Estimation and Control Library (ECL). All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in * the documentation and/or other materials provided with the * distribution. * 3. Neither the name ECL nor the names of its contributors may be * used to endorse or promote products derived from this software * without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE * POSSIBILITY OF SUCH DAMAGE. * ****************************************************************************/ /** * @file ecl_l1_pos_controller.h * Implementation of L1 position control. * Authors and acknowledgements in header. * */ #include #include "ecl_l1_pos_controller.h" float ECL_L1_Pos_Controller::nav_roll() { float ret = atanf(_lateral_accel * 1.0f / CONSTANTS_ONE_G); ret = math::constrain(ret, -_roll_lim_rad, _roll_lim_rad); return ret; } float ECL_L1_Pos_Controller::nav_lateral_acceleration_demand() { return _lateral_accel; } float ECL_L1_Pos_Controller::nav_bearing() { return _wrap_pi(_nav_bearing); } float ECL_L1_Pos_Controller::bearing_error() { return _bearing_error; } float ECL_L1_Pos_Controller::target_bearing() { return _target_bearing; } float ECL_L1_Pos_Controller::switch_distance(float wp_radius) { /* following [2], switching on L1 distance */ return math::min(wp_radius, _L1_distance); } bool ECL_L1_Pos_Controller::reached_loiter_target() { return _circle_mode; } float ECL_L1_Pos_Controller::crosstrack_error() { return _crosstrack_error; } void ECL_L1_Pos_Controller::navigate_waypoints(const math::Vector<2> &vector_A, const math::Vector<2> &vector_B, const math::Vector<2> &vector_curr_position, const math::Vector<2> &ground_speed_vector) { /* this follows the logic presented in [1] */ float eta; float xtrack_vel; float ltrack_vel; /* get the direction between the last (visited) and next waypoint */ _target_bearing = get_bearing_to_next_waypoint(vector_curr_position(0), vector_curr_position(1), vector_B(0), vector_B(1)); /* enforce a minimum ground speed of 0.1 m/s to avoid singularities */ float ground_speed = math::max(ground_speed_vector.length(), 0.1f); /* calculate the L1 length required for the desired period */ _L1_distance = _L1_ratio * ground_speed; /* calculate vector from A to B */ math::Vector<2> vector_AB = get_local_planar_vector(vector_A, vector_B); /* * check if waypoints are on top of each other. If yes, * skip A and directly continue to B */ if (vector_AB.length() < 1.0e-6f) { vector_AB = get_local_planar_vector(vector_curr_position, vector_B); } vector_AB.normalize(); /* calculate the vector from waypoint A to the aircraft */ math::Vector<2> vector_A_to_airplane = get_local_planar_vector(vector_A, vector_curr_position); /* calculate crosstrack error (output only) */ _crosstrack_error = vector_AB % vector_A_to_airplane; /* * If the current position is in a +-135 degree angle behind waypoint A * and further away from A than the L1 distance, then A becomes the L1 point. * If the aircraft is already between A and B normal L1 logic is applied. */ float distance_A_to_airplane = vector_A_to_airplane.length(); float alongTrackDist = vector_A_to_airplane * vector_AB; /* estimate airplane position WRT to B */ math::Vector<2> vector_B_to_P_unit = get_local_planar_vector(vector_B, vector_curr_position).normalized(); /* calculate angle of airplane position vector relative to line) */ // XXX this could probably also be based solely on the dot product float AB_to_BP_bearing = atan2f(vector_B_to_P_unit % vector_AB, vector_B_to_P_unit * vector_AB); /* extension from [2], fly directly to A */ if (distance_A_to_airplane > _L1_distance && alongTrackDist / math::max(distance_A_to_airplane , 1.0f) < -0.7071f) { /* calculate eta to fly to waypoint A */ /* unit vector from waypoint A to current position */ math::Vector<2> vector_A_to_airplane_unit = vector_A_to_airplane.normalized(); /* velocity across / orthogonal to line */ xtrack_vel = ground_speed_vector % (-vector_A_to_airplane_unit); /* velocity along line */ ltrack_vel = ground_speed_vector * (-vector_A_to_airplane_unit); eta = atan2f(xtrack_vel, ltrack_vel); /* bearing from current position to L1 point */ _nav_bearing = atan2f(-vector_A_to_airplane_unit(1) , -vector_A_to_airplane_unit(0)); /* * If the AB vector and the vector from B to airplane point in the same * direction, we have missed the waypoint. At +- 90 degrees we are just passing it. */ } else if (fabsf(AB_to_BP_bearing) < math::radians(100.0f)) { /* * Extension, fly back to waypoint. * * This corner case is possible if the system was following * the AB line from waypoint A to waypoint B, then is * switched to manual mode (or otherwise misses the waypoint) * and behind the waypoint continues to follow the AB line. */ /* calculate eta to fly to waypoint B */ /* velocity across / orthogonal to line */ xtrack_vel = ground_speed_vector % (-vector_B_to_P_unit); /* velocity along line */ ltrack_vel = ground_speed_vector * (-vector_B_to_P_unit); eta = atan2f(xtrack_vel, ltrack_vel); /* bearing from current position to L1 point */ _nav_bearing = atan2f(-vector_B_to_P_unit(1) , -vector_B_to_P_unit(0)); } else { /* calculate eta to fly along the line between A and B */ /* velocity across / orthogonal to line */ xtrack_vel = ground_speed_vector % vector_AB; /* velocity along line */ ltrack_vel = ground_speed_vector * vector_AB; /* calculate eta2 (angle of velocity vector relative to line) */ float eta2 = atan2f(xtrack_vel, ltrack_vel); /* calculate eta1 (angle to L1 point) */ float xtrackErr = vector_A_to_airplane % vector_AB; float sine_eta1 = xtrackErr / math::max(_L1_distance , 0.1f); /* limit output to 45 degrees */ sine_eta1 = math::constrain(sine_eta1, -0.7071f, 0.7071f); //sin(pi/4) = 0.7071 float eta1 = asinf(sine_eta1); eta = eta1 + eta2; /* bearing from current position to L1 point */ _nav_bearing = atan2f(vector_AB(1), vector_AB(0)) + eta1; } /* limit angle to +-90 degrees */ eta = math::constrain(eta, (-M_PI_F) / 2.0f, +M_PI_F / 2.0f); _lateral_accel = _K_L1 * ground_speed * ground_speed / _L1_distance * sinf(eta); /* flying to waypoints, not circling them */ _circle_mode = false; /* the bearing angle, in NED frame */ _bearing_error = eta; } void ECL_L1_Pos_Controller::navigate_loiter(const math::Vector<2> &vector_A, const math::Vector<2> &vector_curr_position, float radius, int8_t loiter_direction, const math::Vector<2> &ground_speed_vector) { /* the complete guidance logic in this section was proposed by [2] */ /* calculate the gains for the PD loop (circle tracking) */ float omega = (2.0f * M_PI_F / _L1_period); float K_crosstrack = omega * omega; float K_velocity = 2.0f * _L1_damping * omega; /* update bearing to next waypoint */ _target_bearing = get_bearing_to_next_waypoint(vector_curr_position(0), vector_curr_position(1), vector_A(0), vector_A(1)); /* ground speed, enforce minimum of 0.1 m/s to avoid singularities */ float ground_speed = math::max(ground_speed_vector.length() , 0.1f); /* calculate the L1 length required for the desired period */ _L1_distance = _L1_ratio * ground_speed; /* calculate the vector from waypoint A to current position */ math::Vector<2> vector_A_to_airplane = get_local_planar_vector(vector_A, vector_curr_position); math::Vector<2> vector_A_to_airplane_unit; /* prevent NaN when normalizing */ if (vector_A_to_airplane.length() > FLT_EPSILON) { /* store the normalized vector from waypoint A to current position */ vector_A_to_airplane_unit = vector_A_to_airplane.normalized(); } else { vector_A_to_airplane_unit = vector_A_to_airplane; } /* calculate eta angle towards the loiter center */ /* velocity across / orthogonal to line from waypoint to current position */ float xtrack_vel_center = vector_A_to_airplane_unit % ground_speed_vector; /* velocity along line from waypoint to current position */ float ltrack_vel_center = - (ground_speed_vector * vector_A_to_airplane_unit); float eta = atan2f(xtrack_vel_center, ltrack_vel_center); /* limit eta to 90 degrees */ eta = math::constrain(eta, -M_PI_F / 2.0f, +M_PI_F / 2.0f); /* calculate the lateral acceleration to capture the center point */ float lateral_accel_sp_center = _K_L1 * ground_speed * ground_speed / _L1_distance * sinf(eta); /* for PD control: Calculate radial position and velocity errors */ /* radial velocity error */ float xtrack_vel_circle = -ltrack_vel_center; /* radial distance from the loiter circle (not center) */ float xtrack_err_circle = vector_A_to_airplane.length() - radius; /* cross track error for feedback */ _crosstrack_error = xtrack_err_circle; /* calculate PD update to circle waypoint */ float lateral_accel_sp_circle_pd = (xtrack_err_circle * K_crosstrack + xtrack_vel_circle * K_velocity); /* calculate velocity on circle / along tangent */ float tangent_vel = xtrack_vel_center * loiter_direction; /* prevent PD output from turning the wrong way */ if (tangent_vel < 0.0f) { lateral_accel_sp_circle_pd = math::max(lateral_accel_sp_circle_pd , 0.0f); } /* calculate centripetal acceleration setpoint */ float lateral_accel_sp_circle_centripetal = tangent_vel * tangent_vel / math::max((0.5f * radius) , (radius + xtrack_err_circle)); /* add PD control on circle and centripetal acceleration for total circle command */ float lateral_accel_sp_circle = loiter_direction * (lateral_accel_sp_circle_pd + lateral_accel_sp_circle_centripetal); /* * Switch between circle (loiter) and capture (towards waypoint center) mode when * the commands switch over. Only fly towards waypoint if outside the circle. */ // XXX check switch over if ((lateral_accel_sp_center < lateral_accel_sp_circle && loiter_direction > 0 && xtrack_err_circle > 0.0f) || (lateral_accel_sp_center > lateral_accel_sp_circle && loiter_direction < 0 && xtrack_err_circle > 0.0f)) { _lateral_accel = lateral_accel_sp_center; _circle_mode = false; /* angle between requested and current velocity vector */ _bearing_error = eta; /* bearing from current position to L1 point */ _nav_bearing = atan2f(-vector_A_to_airplane_unit(1) , -vector_A_to_airplane_unit(0)); } else { _lateral_accel = lateral_accel_sp_circle; _circle_mode = true; _bearing_error = 0.0f; /* bearing from current position to L1 point */ _nav_bearing = atan2f(-vector_A_to_airplane_unit(1) , -vector_A_to_airplane_unit(0)); } } void ECL_L1_Pos_Controller::navigate_heading(float navigation_heading, float current_heading, const math::Vector<2> &ground_speed_vector) { /* the complete guidance logic in this section was proposed by [2] */ float eta; /* * As the commanded heading is the only reference * (and no crosstrack correction occurs), * target and navigation bearing become the same */ _target_bearing = _nav_bearing = _wrap_pi(navigation_heading); eta = _target_bearing - _wrap_pi(current_heading); eta = _wrap_pi(eta); /* consequently the bearing error is exactly eta: */ _bearing_error = eta; /* ground speed is the length of the ground speed vector */ float ground_speed = ground_speed_vector.length(); /* adjust L1 distance to keep constant frequency */ _L1_distance = ground_speed / _heading_omega; float omega_vel = ground_speed * _heading_omega; /* not circling a waypoint */ _circle_mode = false; /* navigating heading means by definition no crosstrack error */ _crosstrack_error = 0; /* limit eta to 90 degrees */ eta = math::constrain(eta, (-M_PI_F) / 2.0f, +M_PI_F / 2.0f); _lateral_accel = 2.0f * sinf(eta) * omega_vel; } void ECL_L1_Pos_Controller::navigate_level_flight(float current_heading) { /* the logic in this section is trivial, but originally proposed by [2] */ /* reset all heading / error measures resulting in zero roll */ _target_bearing = current_heading; _nav_bearing = current_heading; _bearing_error = 0; _crosstrack_error = 0; _lateral_accel = 0; /* not circling a waypoint when flying level */ _circle_mode = false; } math::Vector<2> ECL_L1_Pos_Controller::get_local_planar_vector(const math::Vector<2> &origin, const math::Vector<2> &target) const { /* this is an approximation for small angles, proposed by [2] */ math::Vector<2> out(math::radians((target(0) - origin(0))), math::radians((target(1) - origin(1))*cosf(math::radians(origin(0))))); return out * static_cast(CONSTANTS_RADIUS_OF_EARTH); }