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Diffstat (limited to 'src/lib/ecl/l1/ecl_l1_pos_controller.cpp')
| -rw-r--r-- | src/lib/ecl/l1/ecl_l1_pos_controller.cpp | 366 |
1 files changed, 366 insertions, 0 deletions
diff --git a/src/lib/ecl/l1/ecl_l1_pos_controller.cpp b/src/lib/ecl/l1/ecl_l1_pos_controller.cpp new file mode 100644 index 000000000..27d76f959 --- /dev/null +++ b/src/lib/ecl/l1/ecl_l1_pos_controller.cpp @@ -0,0 +1,366 @@ +/**************************************************************************** + * + * 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 "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::max(wp_radius, _L1_distance); +} + +bool ECL_L1_Pos_Controller::reached_loiter_target(void) +{ + return _circle_mode; +} + +float ECL_L1_Pos_Controller::crosstrack_error(void) +{ + return _crosstrack_error; +} + +void ECL_L1_Pos_Controller::navigate_waypoints(const math::Vector2f &vector_A, const math::Vector2f &vector_B, const math::Vector2f &vector_curr_position, + const math::Vector2f &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.getX(), vector_curr_position.getY(), vector_B.getX(), vector_B.getY()); + + /* 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::Vector2f 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::Vector2f 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::Vector2f 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::Vector2f 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.getY() , -vector_A_to_airplane_unit.getX()); + + /* + * 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.getY() , -vector_B_to_P_unit.getX()); + + } 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.getY(), vector_AB.getX()) + 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::Vector2f &vector_A, const math::Vector2f &vector_curr_position, float radius, int8_t loiter_direction, + const math::Vector2f &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.getX(), vector_curr_position.getY(), vector_A.getX(), vector_A.getY()); + + /* 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::Vector2f vector_A_to_airplane = get_local_planar_vector(vector_A, vector_curr_position); + + /* store the normalized vector from waypoint A to current position */ + math::Vector2f vector_A_to_airplane_unit = (vector_A_to_airplane).normalized(); + + /* 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.getY() , -vector_A_to_airplane_unit.getX()); + + } 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.getY() , -vector_A_to_airplane_unit.getX()); + } +} + + +void ECL_L1_Pos_Controller::navigate_heading(float navigation_heading, float current_heading, const math::Vector2f &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::Vector2f ECL_L1_Pos_Controller::get_local_planar_vector(const math::Vector2f &origin, const math::Vector2f &target) const +{ + /* this is an approximation for small angles, proposed by [2] */ + + math::Vector2f out; + + out.setX(math::radians((target.getX() - origin.getX()))); + out.setY(math::radians((target.getY() - origin.getY())*cosf(math::radians(origin.getX())))); + + return out * static_cast<float>(CONSTANTS_RADIUS_OF_EARTH); +} + |