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npfg: rearrange eval method, handle case in front of starting point of path segment

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Thomas Stastny 2021-08-25 00:09:46 +02:00 committed by JaeyoungLim
parent 4d11b4e06c
commit c70df1e324
2 changed files with 84 additions and 35 deletions
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100
src/lib/npfg/npfg.cpp
View File

@ -47,8 +47,9 @@
using matrix::Vector2d;
using matrix::Vector2f;
void NPFG::evaluate(const Vector2f &ground_vel, const Vector2f &wind_vel,
const Vector2f &unit_path_tangent, const float signed_track_error, const float path_curvature)
void NPFG::evaluate(const Vector2f &ground_vel, const Vector2f &wind_vel, Vector2f &unit_path_tangent,
float signed_track_error, const float path_curvature, bool in_front_of_wp /*= false*/,
const Vector2f &bearing_vec_to_point /*= Vector2f{0.0f, 0.0f}*/)
{
const float ground_speed = ground_vel.norm();
@ -62,16 +63,18 @@ void NPFG::evaluate(const Vector2f &ground_vel, const Vector2f &wind_vel,
airspeed_ref_ = airspeed_nom_;
lateral_accel_ = 0.0f;
feas_ = 0.0f;
feas_on_track_ = 0.0f;
return;
}
const float wind_speed = wind_vel.norm();
const float wind_ratio = wind_speed / airspeed;
const float track_error = fabsf(signed_track_error);
float track_error = fabsf(signed_track_error);
const float wind_cross_upt = cross2D(wind_vel, unit_path_tangent);
const float wind_dot_upt = wind_vel.dot(unit_path_tangent);
// on-track wind triangle projections
float wind_cross_upt = cross2D(wind_vel, unit_path_tangent);
float wind_dot_upt = wind_vel.dot(unit_path_tangent);
// calculate the bearing feasibility on the track at the current closest point
feas_on_track_ = bearingFeasibility(wind_cross_upt, wind_dot_upt, wind_speed, wind_ratio);
@ -85,21 +88,55 @@ void NPFG::evaluate(const Vector2f &ground_vel, const Vector2f &wind_vel,
// track error bound is dynamic depending on ground speed
track_error_bound_ = trackErrorBound(ground_speed, time_const_);
const float normalized_track_error = normalizedTrackError(track_error, track_error_bound_);
float normalized_track_error = normalizedTrackError(track_error, track_error_bound_);
// look ahead angle based purely on track proximity
const float look_ahead_ang = lookAheadAngle(normalized_track_error);
float look_ahead_ang = lookAheadAngle(normalized_track_error);
bearing_vec_ = bearingVec(unit_path_tangent, look_ahead_ang, signed_track_error);
float wind_cross_bearing = cross2D(wind_vel, bearing_vec_);
float wind_dot_bearing = wind_vel.dot(bearing_vec_);
// specific waypoint logic complications... handles case where we are following
// waypoints and are in front of the first of the segment.
// TODO: find a way to get this out of the main eval method!
if (in_front_of_wp && unit_path_tangent.dot(bearing_vec_) < unit_path_tangent.dot(bearing_vec_to_point)) {
// we are in front of the first waypoint and the bearing to the point is
// shallower than that to the line. reset path params to fly directly to
// the first waypoint.
// TODO: probably better to blend these instead of hard switching (could
// effect the adaptive tuning if we switch between these cases with wind
// gusts)
// pretend we are on track, recalculate necessary quantities
signed_track_error = 0.0f;
normalized_track_error = 0.0f;
unit_path_tangent = bearing_vec_to_point;
bearing_vec_ = bearing_vec_to_point;
look_ahead_ang = 0.0f;
wind_cross_upt = cross2D(wind_vel, unit_path_tangent);
wind_dot_upt = wind_vel.dot(unit_path_tangent);
feas_on_track_ = bearingFeasibility(wind_cross_upt, wind_dot_upt, wind_speed, wind_ratio);
adapted_period_ = adaptPeriod(ground_speed, airspeed, wind_ratio, track_error,
path_curvature, wind_vel, unit_path_tangent, feas_on_track_);
p_gain_ = pGain(adapted_period_, damping_);
time_const_ = timeConst(adapted_period_, damping_);
}
track_proximity_ = trackProximity(look_ahead_ang);
// wind triangle projections
const float wind_cross_bearing = cross2D(wind_vel, bearing_vec_);
const float wind_dot_bearing = wind_vel.dot(bearing_vec_);
// continuous representation of the bearing feasibility
feas_ = bearingFeasibility(wind_cross_bearing, wind_dot_bearing, wind_speed, wind_ratio);
// we consider feasibility of both the current bearing as well as that on the track at the current closest point
float feas_combined = feas_ * feas_on_track_;
const float feas_combined = feas_ * feas_on_track_;
min_ground_speed_ref_ = minGroundSpeed(normalized_track_error, feas_combined);
@ -110,16 +147,18 @@ void NPFG::evaluate(const Vector2f &ground_vel, const Vector2f &wind_vel,
wind_dot_bearing, wind_speed, min_ground_speed_ref_);
airspeed_ref_ = air_vel_ref_.norm();
track_proximity_ = trackProximity(look_ahead_ang);
// lateral acceleration demand based on heading error
const float lateral_accel = lateralAccel(air_vel, air_vel_ref_, airspeed);
// lateral acceleration needed to stay on curved track (assuming no heading error)
lateral_accel_ff_ = lateralAccelFF(unit_path_tangent, ground_vel,
wind_dot_upt, wind_cross_upt, airspeed, wind_speed, wind_ratio,
signed_track_error, path_curvature, track_proximity_, feas_combined);
lateral_accel_ff_ = lateralAccelFF(unit_path_tangent, ground_vel, wind_dot_upt,
wind_cross_upt, airspeed, wind_speed, wind_ratio, signed_track_error, path_curvature);
// total lateral acceleration to drive aircaft towards track as well as account
// for path curvature
lateral_accel_ = lateralAccel(air_vel, air_vel_ref_, airspeed) + lateral_accel_ff_;
// for path curvature. The full effect of the feed-forward acceleration is smoothly
// ramped in as the vehicle approaches the track and is further smoothly
// zeroed out as the bearing becomes infeasible.
lateral_accel_ = lateral_accel + feas_combined * track_proximity_ * lateral_accel_ff_;
} // evaluate
float NPFG::adaptPeriod(const float ground_speed, const float airspeed, const float wind_ratio,
@ -431,14 +470,14 @@ float NPFG::bearingFeasibility(const float wind_cross_bearing, const float wind_
float NPFG::lateralAccelFF(const Vector2f &unit_path_tangent, const Vector2f &ground_vel,
const float wind_dot_upt, const float wind_cross_upt, const float airspeed,
const float wind_speed, const float wind_ratio, const float signed_track_error,
const float path_curvature, const float track_proximity, const float feas) const
const float path_curvature) const
{
// NOTE: all calculations within this function take place at the closet point
// on the path, as if the aircraft were already tracking the given path at
// this point with zero angular error. this allows us to evaluate curvature
// induced requirements for lateral acceleration incrementation and ramp them
// in with the track proximity. further the bearing feasibility is considered
// in excess wind conditions.
// in with the track proximity and further consider the bearing feasibility
// in excess wind conditions (this is done external to this method).
// path frame curvature is the instantaneous curvature at our current distance
// from the actual path (considering e.g. concentric circles emanating outward/inward)
@ -457,7 +496,7 @@ float NPFG::lateralAccelFF(const Vector2f &unit_path_tangent, const Vector2f &gr
// note the use of airspeed * speed_ratio as oppose to ground_speed^2 here --
// the prior considers that we command lateral acceleration in the air mass
// relative frame while the latter does not
return airspeed * track_proximity * feas * speed_ratio * path_frame_rate;
return airspeed * speed_ratio * path_frame_rate;
} // lateralAccelFF
float NPFG::lateralAccel(const Vector2f &air_vel, const Vector2f &air_vel_ref, const float airspeed) const
@ -486,27 +525,36 @@ void NPFG::navigateWaypoints(const Vector2d &waypoint_A, const Vector2d &waypoin
const Vector2d &vehicle_pos, const Vector2f &ground_vel, const Vector2f &wind_vel)
{
// similar to logic found in ECL_L1_Pos_Controller method of same name
// BUT no arbitrary max approach angle, approach entirely determined by generated
// bearing vectors
path_type_loiter_ = false;
Vector2f vector_A_to_B = getLocalPlanarVector(waypoint_A, waypoint_B);
Vector2f vector_A_to_vehicle = getLocalPlanarVector(waypoint_A, vehicle_pos);
if (vector_A_to_B.norm() < EPSILON || vector_A_to_B.dot(vector_A_to_vehicle) < 0.0f) {
// the waypoints are either on top of each other and should be considered
// as single waypoint, or we are in front of waypoint A. in either case,
// fly directly to A.
if (vector_A_to_B.norm() < EPSILON) {
// the waypoints are on top of each other and should be considered as a
// single waypoint, fly directly to it
unit_path_tangent_ = -vector_A_to_vehicle.normalized();
signed_track_error_ = 0.0f;
evaluate(ground_vel, wind_vel, unit_path_tangent_, signed_track_error_, 0.0f);
} else if (vector_A_to_B.dot(vector_A_to_vehicle) < 0.0f) {
// we are in front of waypoint A, fly directly to it until the bearing generated
// to the line segement between A and B is shallower than that from the
// bearing to the first waypoint (A).
unit_path_tangent_ = vector_A_to_B.normalized();
signed_track_error_ = cross2D(unit_path_tangent_, vector_A_to_vehicle);
evaluate(ground_vel, wind_vel, unit_path_tangent_, signed_track_error_, 0.0f, true, -vector_A_to_vehicle.normalized());
} else {
// track the line segment between A and B
unit_path_tangent_ = vector_A_to_B.normalized();
signed_track_error_ = cross2D(unit_path_tangent_, vector_A_to_vehicle);
evaluate(ground_vel, wind_vel, unit_path_tangent_, signed_track_error_, 0.0f);
}
evaluate(ground_vel, wind_vel, unit_path_tangent_, signed_track_error_, 0.0f);
updateRollSetpoint();
} // navigateWaypoints

19
src/lib/npfg/npfg.hpp
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@ -402,11 +402,17 @@ private:
* @param[in] unit_path_tangent Unit vector tangent to path at closest point
* in direction of path
* @param[in] signed_track_error Signed error to track at closest point (sign
* determined by path normal direction) [m]
* determined by path normal direction) [m]
* @param[in] path_curvature Path curvature at closest point on track [m^-1]
* @param[in] in_front_of_wp True if we are in front of the starting point of
* a path segment
* @param[in] bearing_vec_to_point Bearing vector to starting point of path
* segment, if relevant
*/
void evaluate(const matrix::Vector2f &ground_vel, const matrix::Vector2f &wind_vel,
const matrix::Vector2f &unit_path_tangent, const float signed_track_error, const float path_curvature);
matrix::Vector2f &unit_path_tangent, float signed_track_error,
const float path_curvature, bool in_front_of_wp = false,
const matrix::Vector2f &bearing_vec_to_point = matrix::Vector2f{0.0f, 0.0f});
/*
* Adapts the controller period considering user defined inputs, current flight
@ -625,9 +631,7 @@ private:
/*
* Calculates an additional feed-forward lateral acceleration demand considering
* the path curvature. The full effect of the acceleration increment is smoothly
* ramped in as the vehicle approaches the track and is further smoothly
* zeroed out as the bearing becomes infeasible.
* the path curvature.
*
* @param[in] unit_path_tangent Unit vector tangent to path at closest point
* in direction of path
@ -639,15 +643,12 @@ private:
* @param[in] signed_track_error Signed error to track at closest point (sign
* determined by path normal direction) [m]
* @param[in] path_curvature Path curvature at closest point on track [m^-1]
* @param[in] track_proximity Smoothing parameter based on vehicle proximity
* to track with values between 0 (at track error boundary) and 1 (on track)
* @param[in] feas Bearing feasibility
* @return Feed-forward lateral acceleration command [m/s^2]
*/
float lateralAccelFF(const matrix::Vector2f &unit_path_tangent, const matrix::Vector2f &ground_vel,
const float wind_dot_upt, const float wind_cross_upt, const float airspeed,
const float wind_speed, const float wind_ratio, const float signed_track_error,
const float path_curvature, const float track_proximity, const float feas) const;
const float path_curvature) const;
/*
* Calculates a lateral acceleration demand from the heading error.