guidance_indi_hybrid.c

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/*
 * Copyright (C) 2015 Ewoud Smeur <ewoud.smeur@gmail.com>
 *
 * 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, write to
 * the Free Software Foundation, 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */
 
#include "generated/airframe.h"
#include "firmwares/rotorcraft/guidance/guidance_indi_hybrid.h"
#include "subsystems/ins/ins_int.h"
#include "subsystems/radio_control.h"
#include "state.h"
#include "subsystems/imu.h"
#include "firmwares/rotorcraft/guidance/guidance_h.h"
#include "firmwares/rotorcraft/guidance/guidance_v.h"
#include "firmwares/rotorcraft/stabilization/stabilization_attitude.h"
#include "firmwares/rotorcraft/autopilot_rc_helpers.h"
#include "mcu_periph/sys_time.h"
#include "autopilot.h"
#include "stabilization/stabilization_attitude_ref_quat_int.h"
#include "firmwares/rotorcraft/stabilization.h"
#include "stdio.h"
#include "filters/low_pass_filter.h"
#include "subsystems/abi.h"
#include "firmwares/rotorcraft/stabilization/stabilization_attitude_rc_setpoint.h"
 
 
// The acceleration reference is calculated with these gains. If you use GPS,
// they are probably limited by the update rate of your GPS. The default
// values are tuned for 4 Hz GPS updates. If you have high speed position updates, the
// gains can be higher, depending on the speed of the inner loop.
#ifndef GUIDANCE_INDI_SPEED_GAIN
#define GUIDANCE_INDI_SPEED_GAIN 1.8
#define GUIDANCE_INDI_SPEED_GAINZ 1.8
#endif
 
#ifndef GUIDANCE_INDI_POS_GAIN
#define GUIDANCE_INDI_POS_GAIN = 0.5;
#define GUIDANCE_INDI_POS_GAINZ = 0.5;
#endif
 
struct guidance_indi_hybrid_params gih_params = {
  .pos_gain = GUIDANCE_INDI_POS_GAIN,
  .pos_gainz = GUIDANCE_INDI_POS_GAINZ,
 
  .speed_gain = GUIDANCE_INDI_SPEED_GAIN,
  .speed_gainz = GUIDANCE_INDI_SPEED_GAINZ,
};
 
#ifdef GUIDANCE_INDI_MAX_AIRSPEED
// Max ground speed that will be commanded
#define NAV_MAX_SPEED (GUIDANCE_INDI_MAX_AIRSPEED + 10.0)
float nav_max_speed = NAV_MAX_SPEED;
#endif
#ifndef MAX_DECELERATION
#define MAX_DECELERATION 1.
#endif
 
struct FloatVect3 sp_accel = {0.0,0.0,0.0};
#ifdef GUIDANCE_INDI_SPECIFIC_FORCE_GAIN
float thrust_in_specific_force_gain = GUIDANCE_INDI_SPECIFIC_FORCE_GAIN;
static void guidance_indi_filter_thrust(void);
 
#ifndef GUIDANCE_INDI_THRUST_DYNAMICS
#ifndef STABILIZATION_INDI_ACT_DYN_P
#error "You need to define GUIDANCE_INDI_THRUST_DYNAMICS to be able to use indi vertical control"
#else // assume that the same actuators are used for thrust as for roll (e.g. quadrotor)
#define GUIDANCE_INDI_THRUST_DYNAMICS STABILIZATION_INDI_ACT_DYN_P
#endif
#endif //GUIDANCE_INDI_THRUST_DYNAMICS
 
#endif //GUIDANCE_INDI_SPECIFIC_FORCE_GAIN
 
#ifndef GUIDANCE_INDI_FILTER_CUTOFF
#ifdef STABILIZATION_INDI_FILT_CUTOFF
#define GUIDANCE_INDI_FILTER_CUTOFF STABILIZATION_INDI_FILT_CUTOFF
#else
#define GUIDANCE_INDI_FILTER_CUTOFF 3.0
#endif
#endif
 
#ifndef GUIDANCE_INDI_MAX_AIRSPEED
#error "You must have an airspeed sensor to use this guidance"
#endif
float guidance_indi_max_airspeed = GUIDANCE_INDI_MAX_AIRSPEED;
 
float inv_eff[4];
 
float lift_pitch_eff = GUIDANCE_INDI_PITCH_LIFT_EFF;
 
struct FloatEulers eulers_zxy;
 
float thrust_act = 0;
Butterworth2LowPass filt_accel_ned[3];
Butterworth2LowPass roll_filt;
Butterworth2LowPass pitch_filt;
Butterworth2LowPass thrust_filt;
Butterworth2LowPass accely_filt;
 
struct FloatVect2 desired_airspeed;
 
struct FloatMat33 Ga;
struct FloatMat33 Ga_inv;
struct FloatVect3 euler_cmd;
 
float filter_cutoff = GUIDANCE_INDI_FILTER_CUTOFF;
 
struct FloatEulers guidance_euler_cmd;
float thrust_in;
 
struct FloatVect3 speed_sp = {0.0, 0.0, 0.0};
 
void guidance_indi_propagate_filters(void);
static void guidance_indi_calcg_wing(struct FloatMat33 *Gmat);
static float guidance_indi_get_liftd(float pitch, float theta);
struct FloatVect3 nav_get_speed_sp_from_go(struct EnuCoor_i target, float pos_gain);
struct FloatVect3 nav_get_speed_sp_from_line(struct FloatVect2 line_v_enu, struct FloatVect2 to_end_v_enu, struct EnuCoor_i target, float pos_gain);
struct FloatVect3 nav_get_speed_setpoint(float pos_gain);
 
void guidance_indi_init(void)
{
  /*AbiBindMsgACCEL_SP(GUIDANCE_INDI_ACCEL_SP_ID, &accel_sp_ev, accel_sp_cb);*/
 
  float tau = 1.0/(2.0*M_PI*filter_cutoff);
  float sample_time = 1.0/PERIODIC_FREQUENCY;
  for(int8_t i=0; i<3; i++) {
    init_butterworth_2_low_pass(&filt_accel_ned[i], tau, sample_time, 0.0);
  }
  init_butterworth_2_low_pass(&roll_filt, tau, sample_time, 0.0);
  init_butterworth_2_low_pass(&pitch_filt, tau, sample_time, 0.0);
  init_butterworth_2_low_pass(&thrust_filt, tau, sample_time, 0.0);
  init_butterworth_2_low_pass(&accely_filt, tau, sample_time, 0.0);
}
 
void guidance_indi_enter(void) {
  thrust_in = 0.0;
  thrust_act = 0;
}
 
#include "firmwares/rotorcraft/navigation.h"
void guidance_indi_run(float *heading_sp) {
 
  /*Obtain eulers with zxy rotation order*/
  float_eulers_of_quat_zxy(&eulers_zxy, stateGetNedToBodyQuat_f());
 
  /*Calculate the transition percentage so that the ctrl_effecitveness scheduling works*/
  transition_percentage = BFP_OF_REAL((eulers_zxy.theta/RadOfDeg(-75.0))*100,INT32_PERCENTAGE_FRAC);
  Bound(transition_percentage,0,BFP_OF_REAL(100.0,INT32_PERCENTAGE_FRAC));
  const int32_t max_offset = ANGLE_BFP_OF_REAL(TRANSITION_MAX_OFFSET);
  transition_theta_offset = INT_MULT_RSHIFT((transition_percentage <<
        (INT32_ANGLE_FRAC - INT32_PERCENTAGE_FRAC)) / 100, max_offset, INT32_ANGLE_FRAC);
 
  //filter accel to get rid of noise and filter attitude to synchronize with accel
  guidance_indi_propagate_filters();
 
  //Linear controller to find the acceleration setpoint from position and velocity
  float pos_x_err = POS_FLOAT_OF_BFP(guidance_h.ref.pos.x) - stateGetPositionNed_f()->x;
  float pos_y_err = POS_FLOAT_OF_BFP(guidance_h.ref.pos.y) - stateGetPositionNed_f()->y;
  float pos_z_err = POS_FLOAT_OF_BFP(guidance_v_z_ref - stateGetPositionNed_i()->z);
 
  if(autopilot.mode == AP_MODE_NAV) {
    speed_sp = nav_get_speed_setpoint(gih_params.pos_gain);
  } else{
    speed_sp.x = pos_x_err * gih_params.pos_gain;
    speed_sp.y = pos_y_err * gih_params.pos_gain;
    speed_sp.z = pos_z_err * gih_params.pos_gainz;
  }
 
  //for rc control horizontal, rotate from body axes to NED
  float psi = eulers_zxy.psi;
  /*NAV mode*/
  float speed_sp_b_x = cosf(psi) * speed_sp.x + sinf(psi) * speed_sp.y;
  float speed_sp_b_y =-sinf(psi) * speed_sp.x + cosf(psi) * speed_sp.y;
 
  float airspeed = stateGetAirspeed_f();
 
  struct NedCoor_f *groundspeed = stateGetSpeedNed_f();
  struct FloatVect2 airspeed_v = {cos(psi)*airspeed, sin(psi)*airspeed};
  struct FloatVect2 windspeed;
  VECT2_DIFF(windspeed, *groundspeed, airspeed_v);
 
  VECT2_DIFF(desired_airspeed, speed_sp, windspeed); // Use 2d part of speed_sp
  float norm_des_as = FLOAT_VECT2_NORM(desired_airspeed);
 
  // Make turn instead of straight line
  if((airspeed > 10.0) && (norm_des_as > 12.0)) {
 
  // Give the wind cancellation priority.
    if (norm_des_as > guidance_indi_max_airspeed) {
      float groundspeed_factor = 0.0;
 
      // if the wind is faster than we can fly, just fly in the wind direction
      if(FLOAT_VECT2_NORM(windspeed) < guidance_indi_max_airspeed) {
        float av = speed_sp.x * speed_sp.x + speed_sp.y * speed_sp.y;
        float bv = -2 * (windspeed.x * speed_sp.x + windspeed.y * speed_sp.y);
        float cv = windspeed.x * windspeed.x + windspeed.y * windspeed.y - guidance_indi_max_airspeed * guidance_indi_max_airspeed;
 
        float dv = bv * bv - 4.0 * av * cv;
 
        // dv can only be positive, but just in case
        if(dv < 0) {
          dv = fabs(dv);
        }
        float d_sqrt = sqrtf(dv);
 
        groundspeed_factor = (-bv + d_sqrt)  / (2 * av);
      }
 
      desired_airspeed.x = groundspeed_factor * speed_sp.x - windspeed.x;
      desired_airspeed.y = groundspeed_factor * speed_sp.y - windspeed.y;
 
      speed_sp_b_x = guidance_indi_max_airspeed;
    }
 
    // desired airspeed can not be larger than max airspeed
    speed_sp_b_x = Min(norm_des_as,guidance_indi_max_airspeed);
 
    // Calculate accel sp in body axes, because we need to regulate airspeed
    struct FloatVect2 sp_accel_b;
    // In turn acceleration proportional to heading diff
    sp_accel_b.y = atan2(desired_airspeed.y, desired_airspeed.x) - psi;
    FLOAT_ANGLE_NORMALIZE(sp_accel_b.y);
    sp_accel_b.y *= GUIDANCE_INDI_HEADING_BANK_GAIN;
 
    // Control the airspeed
    sp_accel_b.x = (speed_sp_b_x - airspeed) * gih_params.speed_gain;
 
    sp_accel.x = cosf(psi) * sp_accel_b.x - sinf(psi) * sp_accel_b.y;
    sp_accel.y = sinf(psi) * sp_accel_b.x + cosf(psi) * sp_accel_b.y;
 
    sp_accel.z = (speed_sp.z - stateGetSpeedNed_f()->z) * gih_params.speed_gainz;
  } else { // Go somewhere in the shortest way
 
    if(airspeed > 10.0) {
      // Groundspeed vector in body frame
      float groundspeed_x = cosf(psi) * stateGetSpeedNed_f()->x + sinf(psi) * stateGetSpeedNed_f()->y;
      float speed_increment = speed_sp_b_x - groundspeed_x;
 
      // limit groundspeed setpoint to max_airspeed + (diff gs and airspeed)
      if((speed_increment + airspeed) > guidance_indi_max_airspeed) {
        speed_sp_b_x = guidance_indi_max_airspeed + groundspeed_x - airspeed;
      }
    }
    speed_sp.x = cosf(psi) * speed_sp_b_x - sinf(psi) * speed_sp_b_y;
    speed_sp.y = sinf(psi) * speed_sp_b_x + cosf(psi) * speed_sp_b_y;
 
    sp_accel.x = (speed_sp.x - stateGetSpeedNed_f()->x) * gih_params.speed_gain;
    sp_accel.y = (speed_sp.y - stateGetSpeedNed_f()->y) * gih_params.speed_gain;
    sp_accel.z = (speed_sp.z - stateGetSpeedNed_f()->z) * gih_params.speed_gainz;
  }
 
  // Bound the acceleration setpoint
  float accelbound = 3.0 + airspeed/guidance_indi_max_airspeed*5.0;
  vect_bound_in_2d(&sp_accel, accelbound);
  /*BoundAbs(sp_accel.x, 3.0 + airspeed/guidance_indi_max_airspeed*6.0);*/
  /*BoundAbs(sp_accel.y, 3.0 + airspeed/guidance_indi_max_airspeed*6.0);*/
  BoundAbs(sp_accel.z, 3.0);
 
#if GUIDANCE_INDI_RC_DEBUG
#warning "GUIDANCE_INDI_RC_DEBUG lets you control the accelerations via RC, but disables autonomous flight!"
  //for rc control horizontal, rotate from body axes to NED
  float psi = eulers_zxy.psi;
  float rc_x = -(radio_control.values[RADIO_PITCH]/9600.0)*8.0;
  float rc_y = (radio_control.values[RADIO_ROLL]/9600.0)*8.0;
  sp_accel.x = cosf(psi) * rc_x - sinf(psi) * rc_y;
  sp_accel.y = sinf(psi) * rc_x + cosf(psi) * rc_y;
 
  //for rc vertical control
  sp_accel.z = -(radio_control.values[RADIO_THROTTLE]-4500)*8.0/9600.0;
#endif
 
  //Calculate matrix of partial derivatives
  guidance_indi_calcg_wing(&Ga);
  //Invert this matrix
  MAT33_INV(Ga_inv, Ga);
 
  struct FloatVect3 accel_filt;
  accel_filt.x = filt_accel_ned[0].o[0];
  accel_filt.y = filt_accel_ned[1].o[0];
  accel_filt.z = filt_accel_ned[2].o[0];
 
  struct FloatVect3 a_diff = { sp_accel.x - accel_filt.x, sp_accel.y - accel_filt.y, sp_accel.z - accel_filt.z};
 
  //Bound the acceleration error so that the linearization still holds
  Bound(a_diff.x, -6.0, 6.0);
  Bound(a_diff.y, -6.0, 6.0);
  Bound(a_diff.z, -9.0, 9.0);
 
  //If the thrust to specific force ratio has been defined, include vertical control
  //else ignore the vertical acceleration error
#ifndef GUIDANCE_INDI_SPECIFIC_FORCE_GAIN
#ifndef STABILIZATION_ATTITUDE_INDI_FULL
  a_diff.z = 0.0;
#endif
#endif
 
  //Calculate roll,pitch and thrust command
  MAT33_VECT3_MUL(euler_cmd, Ga_inv, a_diff);
 
  AbiSendMsgTHRUST(THRUST_INCREMENT_ID, euler_cmd.z);
 
  //Coordinated turn
  //feedforward estimate angular rotation omega = g*tan(phi)/v
  float omega;
  const float max_phi = RadOfDeg(60.0);
  float airspeed_turn = airspeed;
  //We are dividing by the airspeed, so a lower bound is important
  Bound(airspeed_turn,10.0,30.0);
 
  guidance_euler_cmd.phi = roll_filt.o[0] + euler_cmd.x;
  guidance_euler_cmd.theta = pitch_filt.o[0] + euler_cmd.y;
 
  //Bound euler angles to prevent flipping
  Bound(guidance_euler_cmd.phi, -GUIDANCE_H_MAX_BANK, GUIDANCE_H_MAX_BANK);
  Bound(guidance_euler_cmd.theta, -RadOfDeg(120.0), RadOfDeg(25.0));
 
  float coordinated_turn_roll = guidance_euler_cmd.phi;
 
  if( (guidance_euler_cmd.theta > 0.0) && ( fabs(guidance_euler_cmd.phi) < guidance_euler_cmd.theta)) {
    coordinated_turn_roll = ((guidance_euler_cmd.phi > 0.0) - (guidance_euler_cmd.phi < 0.0))*guidance_euler_cmd.theta;
  }
 
  if (fabs(coordinated_turn_roll) < max_phi) {
    omega = 9.81 / airspeed_turn * tanf(coordinated_turn_roll);
  } else { //max 60 degrees roll
    omega = 9.81 / airspeed_turn * 1.72305 * ((coordinated_turn_roll > 0.0) - (coordinated_turn_roll < 0.0));
  }
 
#ifdef FWD_SIDESLIP_GAIN
  // Add sideslip correction
  omega -= accely_filt.o[0]*FWD_SIDESLIP_GAIN;
#endif
 
#ifndef KNIFE_EDGE_TEST
  *heading_sp += omega / PERIODIC_FREQUENCY;
  FLOAT_ANGLE_NORMALIZE(*heading_sp);
#endif
 
  guidance_euler_cmd.psi = *heading_sp;
 
#ifdef GUIDANCE_INDI_SPECIFIC_FORCE_GAIN
  guidance_indi_filter_thrust();
 
  //Add the increment in specific force * specific_force_to_thrust_gain to the filtered thrust
  thrust_in = thrust_filt.o[0] + euler_cmd.z*thrust_in_specific_force_gain;
  Bound(thrust_in, 0, 9600);
 
#if GUIDANCE_INDI_RC_DEBUG
  if(radio_control.values[RADIO_THROTTLE]<300) {
    thrust_in = 0;
  }
#endif
 
  //Overwrite the thrust command from guidance_v
  stabilization_cmd[COMMAND_THRUST] = thrust_in;
#endif
 
  // Set the quaternion setpoint from eulers_zxy
  struct FloatQuat sp_quat;
  float_quat_of_eulers_zxy(&sp_quat, &guidance_euler_cmd);
  float_quat_normalize(&sp_quat);
  QUAT_BFP_OF_REAL(stab_att_sp_quat,sp_quat);
}
 
#ifdef GUIDANCE_INDI_SPECIFIC_FORCE_GAIN
 
void guidance_indi_filter_thrust(void)
{
  // Actuator dynamics
  thrust_act = thrust_act + GUIDANCE_INDI_THRUST_DYNAMICS * (thrust_in - thrust_act);
 
  // same filter as for the acceleration
  update_butterworth_2_low_pass(&thrust_filt, thrust_act);
}
#endif
 
void guidance_indi_propagate_filters(void) {
  struct NedCoor_f *accel = stateGetAccelNed_f();
  update_butterworth_2_low_pass(&filt_accel_ned[0], accel->x);
  update_butterworth_2_low_pass(&filt_accel_ned[1], accel->y);
  update_butterworth_2_low_pass(&filt_accel_ned[2], accel->z);
 
  update_butterworth_2_low_pass(&roll_filt, eulers_zxy.phi);
  update_butterworth_2_low_pass(&pitch_filt, eulers_zxy.theta);
 
  // Propagate filter for sideslip correction
  float accely = ACCEL_FLOAT_OF_BFP(stateGetAccelBody_i()->y);
  update_butterworth_2_low_pass(&accely_filt, accely);
}
 
void guidance_indi_calcg_wing(struct FloatMat33 *Gmat) {
 
  /*Pre-calculate sines and cosines*/
  float sphi = sinf(eulers_zxy.phi);
  float cphi = cosf(eulers_zxy.phi);
  float stheta = sinf(eulers_zxy.theta);
  float ctheta = cosf(eulers_zxy.theta);
  float spsi = sinf(eulers_zxy.psi);
  float cpsi = cosf(eulers_zxy.psi);
  //minus gravity is a guesstimate of the thrust force, thrust measurement would be better
 
#ifndef GUIDANCE_INDI_PITCH_EFF_SCALING
#define GUIDANCE_INDI_PITCH_EFF_SCALING 1.0
#endif
 
  /*Amount of lift produced by the wing*/
  float pitch_lift = eulers_zxy.theta;
  Bound(pitch_lift,-M_PI_2,0);
  float lift = sinf(pitch_lift)*9.81;
  float T = cosf(pitch_lift)*-9.81;
 
  // get the derivative of the lift wrt to theta
  float liftd = guidance_indi_get_liftd(stateGetAirspeed_f(), eulers_zxy.theta);
 
  RMAT_ELMT(*Gmat, 0, 0) =  cphi*ctheta*spsi*T + cphi*spsi*lift;
  RMAT_ELMT(*Gmat, 1, 0) = -cphi*ctheta*cpsi*T - cphi*cpsi*lift;
  RMAT_ELMT(*Gmat, 2, 0) = -sphi*ctheta*T -sphi*lift;
  RMAT_ELMT(*Gmat, 0, 1) = (ctheta*cpsi - sphi*stheta*spsi)*T*GUIDANCE_INDI_PITCH_EFF_SCALING + sphi*spsi*liftd;
  RMAT_ELMT(*Gmat, 1, 1) = (ctheta*spsi + sphi*stheta*cpsi)*T*GUIDANCE_INDI_PITCH_EFF_SCALING - sphi*cpsi*liftd;
  RMAT_ELMT(*Gmat, 2, 1) = -cphi*stheta*T*GUIDANCE_INDI_PITCH_EFF_SCALING + cphi*liftd;
  RMAT_ELMT(*Gmat, 0, 2) = stheta*cpsi + sphi*ctheta*spsi;
  RMAT_ELMT(*Gmat, 1, 2) = stheta*spsi - sphi*ctheta*cpsi;
  RMAT_ELMT(*Gmat, 2, 2) = cphi*ctheta;
}
 
float guidance_indi_get_liftd(float airspeed, float theta) {
  float liftd = 0.0;
  if(airspeed < 12) {
    float pitch_interp = DegOfRad(theta);
    Bound(pitch_interp, -80.0, -40.0);
    float ratio = (pitch_interp + 40.0)/(-40.);
    liftd = -24.0*ratio;
  } else {
    liftd = -(airspeed - 8.5)*lift_pitch_eff/M_PI*180.0;
  }
  //TODO: bound liftd
  return liftd;
}
 
struct FloatVect3 nav_get_speed_setpoint(float pos_gain) {
  struct FloatVect3 speed_sp;
  if(horizontal_mode == HORIZONTAL_MODE_ROUTE) {
    speed_sp = nav_get_speed_sp_from_line(line_vect, to_end_vect, navigation_target, pos_gain);
  } else {
    speed_sp = nav_get_speed_sp_from_go(navigation_target, pos_gain);
  }
  return speed_sp;
}
 
struct FloatVect3 nav_get_speed_sp_from_line(struct FloatVect2 line_v_enu, struct FloatVect2 to_end_v_enu, struct EnuCoor_i target, float pos_gain) {
 
  // enu -> ned
  struct FloatVect2 line_v = {line_v_enu.y, line_v_enu.x};
  struct FloatVect2 to_end_v = {to_end_v_enu.y, to_end_v_enu.x};
 
  struct NedCoor_f ned_target;
  // Target in NED instead of ENU
  VECT3_ASSIGN(ned_target, POS_FLOAT_OF_BFP(target.y), POS_FLOAT_OF_BFP(target.x), -POS_FLOAT_OF_BFP(target.z));
 
  // Calculate magnitude of the desired speed vector based on distance to waypoint
  float dist_to_target = float_vect2_norm(&to_end_v);
  float desired_speed;
  if(force_forward) {
    desired_speed = nav_max_speed;
  } else {
    desired_speed = dist_to_target * pos_gain;
    Bound(desired_speed, 0.0, nav_max_speed);
  }
 
  // Calculate length of line segment
  float length_line = float_vect2_norm(&line_v);
  if(length_line < 0.01) {
    length_line = 0.01;
  }
 
  //Normal vector to the line, with length of the line
  struct FloatVect2 normalv;
  VECT2_ASSIGN(normalv, -line_v.y, line_v.x);
  // Length of normal vector is the same as of the line segment
  float length_normalv = length_line;
  if(length_normalv < 0.01) {
    length_normalv = 0.01;
  }
 
  // Distance along the normal vector
  float dist_to_line = (to_end_v.x*normalv.x + to_end_v.y*normalv.y)/length_normalv;
 
  // Normal vector scaled to be the distance to the line
  struct FloatVect2 v_to_line, v_along_line;
  v_to_line.x = dist_to_line*normalv.x/length_normalv;
  v_to_line.y = dist_to_line*normalv.y/length_normalv;
 
  // Depending on the normal vector, the distance could be negative
  float dist_to_line_abs = fabs(dist_to_line);
 
  // The distance that needs to be traveled along the line
  /*float dist_along_line = (line_v.x*to_end_v.x + line_v.y*to_end_v.y)/length_line;*/
  v_along_line.x = line_v.x/length_line*50.0;
  v_along_line.y = line_v.y/length_line*50.0;
 
  // Calculate the desired direction to converge to the line
  struct FloatVect2 direction;
  VECT2_SMUL(direction, v_along_line, (1.0/(1+dist_to_line_abs*0.05)));
  VECT2_ADD(direction, v_to_line);
  float length_direction = float_vect2_norm(&direction);
  if(length_direction < 0.01) {
    length_direction = 0.01;
  }
 
  // Scale to have the desired speed
  struct FloatVect2 final_vector;
  VECT2_SMUL(final_vector, direction, desired_speed/length_direction);
 
  struct FloatVect3 speed_sp_return = {final_vector.x, final_vector.y, gih_params.pos_gainz*(ned_target.z - stateGetPositionNed_f()->z)};
  if((guidance_v_mode == GUIDANCE_V_MODE_NAV) && (vertical_mode == VERTICAL_MODE_CLIMB)) {
    speed_sp_return.z = SPEED_FLOAT_OF_BFP(guidance_v_zd_sp);
  }
 
  // Bound vertical speed setpoint
  if(stateGetAirspeed_f() > 13.0) {
    Bound(speed_sp_return.z, -4.0, 5.0);
  } else {
    Bound(speed_sp_return.z, -nav_climb_vspeed, -nav_descend_vspeed);
  }
 
  return speed_sp_return;
}
 
struct FloatVect3 nav_get_speed_sp_from_go(struct EnuCoor_i target, float pos_gain) {
  // The speed sp that will be returned
  struct FloatVect3 speed_sp_return;
  struct NedCoor_f ned_target;
  // Target in NED instead of ENU
  VECT3_ASSIGN(ned_target, POS_FLOAT_OF_BFP(target.y), POS_FLOAT_OF_BFP(target.x), -POS_FLOAT_OF_BFP(target.z));
 
  // Calculate position error
  struct FloatVect3 pos_error;
  struct NedCoor_f *pos = stateGetPositionNed_f();
  VECT3_DIFF(pos_error, ned_target, *pos);
 
  VECT3_SMUL(speed_sp_return, pos_error, pos_gain);
  speed_sp_return.z = gih_params.pos_gainz*pos_error.z;
 
  if((guidance_v_mode == GUIDANCE_V_MODE_NAV) && (vertical_mode == VERTICAL_MODE_CLIMB)) {
    speed_sp_return.z = SPEED_FLOAT_OF_BFP(guidance_v_zd_sp);
  }
 
  if(force_forward) {
    vect_scale(&speed_sp_return, nav_max_speed);
  } else {
    // Calculate distance to waypoint
    float dist_to_wp = FLOAT_VECT2_NORM(pos_error);
    // Calculate max speed to decelerate from
    float max_speed_decel = sqrt(2*dist_to_wp*MAX_DECELERATION);
 
    // Bound the setpoint velocity vector
    float max_h_speed = Min(nav_max_speed, max_speed_decel);
    vect_bound_in_2d(&speed_sp_return, max_h_speed);
  }
 
  // Bound vertical speed setpoint
  if(stateGetAirspeed_f() > 13.0) {
    Bound(speed_sp_return.z, -4.0, 5.0);
  } else {
    Bound(speed_sp_return.z, -nav_climb_vspeed, -nav_descend_vspeed);
  }
 
  return speed_sp_return;
}