approach_moving_target.c

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/*
 * Copyright (C) 2021 Ewoud Smeur <e.j.j.smeur@tudelft.nl>
 *
 * This file is part of paparazzi
 *
 * paparazzi is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * paparazzi is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with paparazzi; see the file COPYING.  If not, see
 * <http://www.gnu.org/licenses/>.
 */
#include "generated/airframe.h"
 
#include "approach_moving_target.h"
 
#include "generated/modules.h"
#include "modules/core/abi.h"
#include "filters/low_pass_filter.h"
 
 
// Filter value in Hz
#ifndef APPROACH_MOVING_TARGET_CUTOFF_FREQ_FILTERS_HZ
#define APPROACH_MOVING_TARGET_CUTOFF_FREQ_FILTERS_HZ 0.5
#endif
 
// Approach slope angle in degrees
#ifndef APPROACH_MOVING_TARGET_SLOPE
#define APPROACH_MOVING_TARGET_SLOPE 35.0
#endif
 
// Approach initial distance in meters
#ifndef APPROACH_MOVING_TARGET_DISTANCE
#define APPROACH_MOVING_TARGET_DISTANCE 60.0
#endif
 
// Approach speed in meters per second along the slope
#ifndef APPROACH_MOVING_TARGET_SPEED
#define APPROACH_MOVING_TARGET_SPEED -1.0
#endif
 
// Gains
#ifndef APPROACH_MOVING_TARGET_ERR_SLOWDOWN_GAIN
#define APPROACH_MOVING_TARGET_ERR_SLOWDOWN_GAIN 0.25
#endif
 
#ifndef APPROACH_MOVING_TARGET_POS_GAIN
#define APPROACH_MOVING_TARGET_POS_GAIN 0.3
#endif
 
#ifndef APPROACH_MOVING_TARGET_SPEED_GAIN
#define APPROACH_MOVING_TARGET_SPEED_GAIN 1.0
#endif
 
#ifndef APPROACH_MOVING_TARGET_RELVEL_GAIN
#define APPROACH_MOVING_TARGET_RELVEL_GAIN 1.0
#endif
 
Butterworth2LowPass target_pos_filt[3];
Butterworth2LowPass target_vel_filt[3];
Butterworth2LowPass target_heading_filt;
 
#define DEBUG_AMT TRUE
#include <stdio.h>
 
struct Amt amt = {
  .distance               = APPROACH_MOVING_TARGET_DISTANCE,
  .speed                  = APPROACH_MOVING_TARGET_SPEED,
  .psi_ref                = 180.0,
  .slope_ref              = APPROACH_MOVING_TARGET_SLOPE,
  .err_slowdown_gain      = APPROACH_MOVING_TARGET_ERR_SLOWDOWN_GAIN,
  .pos_gain               = APPROACH_MOVING_TARGET_POS_GAIN,
  .speed_gain             = APPROACH_MOVING_TARGET_SPEED_GAIN,
  .relvel_gain            = APPROACH_MOVING_TARGET_RELVEL_GAIN,
  .cutoff_freq_filters_hz = APPROACH_MOVING_TARGET_CUTOFF_FREQ_FILTERS_HZ,
  .enabled_time           = 0,
  .wp_id                  = 0,
};
 
struct AmtTelem {
  struct FloatVect3 des_pos;
  struct FloatVect3 des_vel;
};
 
struct AmtTelem amt_telem;
bool approach_moving_target_enabled = false;
 
struct FloatVect3 nav_get_speed_sp_from_diagonal(struct EnuCoor_i target, float pos_gain, float rope_heading);
void update_waypoint(uint8_t wp_id, struct FloatVect3 *target_ned);
 
#if PERIODIC_TELEMETRY
#include "modules/datalink/telemetry.h"
static void send_approach_moving_target(struct transport_tx *trans, struct link_device *dev)
{
  pprz_msg_send_APPROACH_MOVING_TARGET(trans, dev, AC_ID,
                                       &amt_telem.des_pos.x,
                                       &amt_telem.des_pos.y,
                                       &amt_telem.des_pos.z,
                                       &amt_telem.des_vel.x,
                                       &amt_telem.des_vel.y,
                                       &amt_telem.des_vel.z,
                                       &amt.distance);
}
#endif
 
void approach_moving_target_init(void)
{
  approach_moving_target_set_low_pass_freq(amt.cutoff_freq_filters_hz);
#if PERIODIC_TELEMETRY
  register_periodic_telemetry(DefaultPeriodic, PPRZ_MSG_ID_APPROACH_MOVING_TARGET, send_approach_moving_target);
#endif
}
 
void approach_moving_target_set_low_pass_freq(float filter_freq)
{
  amt.cutoff_freq_filters_hz = filter_freq;
  // tau = 1/(2*pi*Fc)
  float tau = 1.0 / (2.0 * M_PI * amt.cutoff_freq_filters_hz);
  float sample_time = 1.0 / FOLLOW_DIAGONAL_APPROACH_FREQ;
  for (uint8_t i = 0; i < 3; i++) {
    init_butterworth_2_low_pass(&target_pos_filt[i], tau, sample_time, 0.0);
    init_butterworth_2_low_pass(&target_vel_filt[i], tau, sample_time, 0.0);
  }
  init_butterworth_2_low_pass(&target_heading_filt, tau, sample_time, 0.0);
 
}
 
// Update a waypoint such that you can see on the GCS where the drone wants to go
void update_waypoint(uint8_t wp_id, struct FloatVect3 *target_ned)
{
 
  // Update the waypoint
  struct EnuCoor_f target_enu;
  ENU_OF_TO_NED(target_enu, *target_ned);
  waypoint_set_enu(wp_id, &target_enu);
 
  // Send waypoint update every half second
  RunOnceEvery(100 / 2, {
    // Send to the GCS that the waypoint has been moved
    DOWNLINK_SEND_WP_MOVED_ENU(DefaultChannel, DefaultDevice, &wp_id,
                               &waypoints[wp_id].enu_i.x,
                               &waypoints[wp_id].enu_i.y,
                               &waypoints[wp_id].enu_i.z);
  });
}
 
// Function to enable from flight plan (call repeatedly!)
void approach_moving_target_enable(uint8_t wp_id)
{
  amt.enabled_time = get_sys_time_msec();
  amt.wp_id = wp_id;
}
 
void follow_diagonal_approach(void)
{
 
  // Check if the flight plan recently called the enable function
  if ((get_sys_time_msec() - amt.enabled_time) > (2000 / NAVIGATION_FREQUENCY)) {
    return;
  }
 
  // Get the target position, velocity and heading
  struct NedCoor_f target_pos, target_vel = {0};
  float target_heading;
  if (!target_get_pos(&target_pos, &target_heading)) {
    // TODO: What to do? Same can be checked for the velocity
    return;
  }
  if (target_heading > 360.f) {
    // TODO: We got an invalid heading and need to do something with it
    return;
  }
  target_get_vel(&target_vel);
 
  // filter target values
  update_butterworth_2_low_pass(&target_pos_filt[0], target_pos.x);
  update_butterworth_2_low_pass(&target_pos_filt[1], target_pos.y);
  update_butterworth_2_low_pass(&target_pos_filt[2], target_pos.z);
 
  update_butterworth_2_low_pass(&target_vel_filt[0], target_vel.x);
  update_butterworth_2_low_pass(&target_vel_filt[1], target_vel.y);
  update_butterworth_2_low_pass(&target_vel_filt[2], target_vel.z);
 
  // just filtering the heading will go wrong if it wraps, instead do:
  // take the diff with current heading_filtered, wrap that, add to current, insert in filter and wrap again?
  // example: target_heading - target_heading_filt (170 - -170 = 340), -> -20 -> -190 -> into filter -> wrap
  float heading_diff = target_heading - target_heading_filt.o[0];
  FLOAT_ANGLE_NORMALIZE(heading_diff);
  float target_heading_input = target_heading_filt.o[0] + heading_diff;
  update_butterworth_2_low_pass(&target_heading_filt, target_heading_input);
  float target_heading_filt_wrapped = target_heading_filt.o[0];
  FLOAT_ANGLE_NORMALIZE(target_heading_filt_wrapped);
 
  target_pos.x = target_pos_filt[0].o[0];
  target_pos.y = target_pos_filt[1].o[0];
  target_pos.z = target_pos_filt[2].o[0];
 
  target_vel.x = target_vel_filt[0].o[0];
  target_vel.y = target_vel_filt[1].o[0];
  target_vel.z = target_vel_filt[2].o[0];
 
  VECT3_SMUL(target_vel, target_vel, amt.speed_gain);
 
  // Reference model
  float gamma_ref = RadOfDeg(amt.slope_ref);
  float psi_ref = RadOfDeg(target_heading_filt_wrapped + amt.psi_ref);
 
  amt.rel_unit_vec.x = cosf(gamma_ref) * cosf(psi_ref);
  amt.rel_unit_vec.y = cosf(gamma_ref) * sinf(psi_ref);
  amt.rel_unit_vec.z = -sinf(gamma_ref);
 
  // desired position = rel_pos + target_pos
  struct FloatVect3 ref_relpos;
  VECT3_SMUL(ref_relpos, amt.rel_unit_vec, amt.distance);
 
  // ATTENTION, target_pos is already relative now!
  struct FloatVect3 des_pos;
  VECT3_SUM(des_pos, ref_relpos, target_pos);
 
  struct FloatVect3 ref_relvel;
  VECT3_SMUL(ref_relvel, amt.rel_unit_vec, amt.speed * amt.relvel_gain);
 
  // error controller
  struct FloatVect3 pos_err;
  struct FloatVect3 ec_vel;
  struct NedCoor_f *drone_pos = stateGetPositionNed_f();
  // ATTENTION, target_pos is already relative now!
  // VECT3_DIFF(pos_err, des_pos, *drone_pos);
  VECT3_COPY(pos_err, des_pos);
  VECT3_SMUL(ec_vel, pos_err, amt.pos_gain);
 
  // desired velocity = rel_vel + target_vel + error_controller(using NED position)
  struct FloatVect3 des_vel = {
    ref_relvel.x + target_vel.x + ec_vel.x,
    ref_relvel.y + target_vel.y + ec_vel.y,
    ref_relvel.z + target_vel.z + ec_vel.z,
  };
 
  float_vect3_bound_in_3d(&des_vel, 10.0);
 
  // Bound vertical speed setpoint
  if (stateGetAirspeed_f() > 13.0) {
    Bound(des_vel.z, -4.0, 5.0);
  } else {
    Bound(des_vel.z, -nav.climb_vspeed, -nav.descend_vspeed);
  }
 
  AbiSendMsgVEL_SP(VEL_SP_FCR_ID, &des_vel);
 
  /* limit the speed such that the vertical component is small enough
  * and doesn't outrun the vehicle
  */
  float min_speed;
  float sin_gamma_ref = sinf(gamma_ref);
  if (sin_gamma_ref > 0.05) {
    min_speed = (nav.descend_vspeed + 0.1) / sin_gamma_ref;
  } else {
    min_speed = -5.0; // prevent dividing by zero
  }
 
  // The upper bound is not very important
  Bound(amt.speed, min_speed, 4.0);
 
  // Reduce approach speed if the error is large
  float norm_pos_err_sq = VECT3_NORM2(pos_err);
  float int_speed = amt.speed / (norm_pos_err_sq * amt.err_slowdown_gain + 1.0);
 
  // integrate speed to get the distance
  float dt = FOLLOW_DIAGONAL_APPROACH_PERIOD;
  amt.distance += int_speed * dt;
 
  // For display purposes
  struct FloatVect3 disp_pos_target;
  VECT3_SUM(disp_pos_target, des_pos, *drone_pos);
  update_waypoint(amt.wp_id, &disp_pos_target);
 
  // Debug target pos:
  VECT3_DIFF(amt_telem.des_pos, *drone_pos, target_pos);
 
  // Update values for telemetry
  VECT3_COPY(amt_telem.des_pos, des_pos);
  VECT3_COPY(amt_telem.des_vel, des_vel);
}