PX4-Autopilot/src/modules/flight_mode_manager/tasks/AutoLineSmoothVel/TrajectoryConstraints.hpp

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#pragma once

#include <px4_defines.h>

#include <matrix/math.hpp>
#include <mathlib/mathlib.h>

namespace math
{
namespace trajectory
{
using matrix::Vector3f;
using matrix::Vector2f;

struct VehicleDynamicLimits {
	float z_accept_rad;
	float xy_accept_rad;

	float max_acc_xy;
	float max_jerk;

	float max_speed_xy;

	// TODO: remove this
	float max_acc_xy_radius_scale;
};

/*
 * Compute the maximum allowed speed at the waypoint assuming that we want to
 * connect the two lines (current-target and target-next)
 * with a tangent circle with constant speed and desired centripetal acceleration: a_centripetal = speed^2 / radius
 * The circle should in theory start and end at the intersection of the lines and the waypoint's acceptance radius.
 * This is not exactly true in reality since Navigator switches the waypoint so we have to take in account that
 * the real acceptance radius is smaller.
 *
 */
inline float computeStartXYSpeedFromWaypoints(const Vector3f &start_position, const Vector3f &target,
		const Vector3f &next_target, float exit_speed, const VehicleDynamicLimits &config)
{
	const float distance_target_next = (target - next_target).xy().norm();

	const bool target_next_different = distance_target_next  > 0.001f;
	const bool waypoint_overlap = distance_target_next < config.xy_accept_rad;
	const bool has_reached_altitude = fabsf(target(2) - start_position(2)) < config.z_accept_rad;
	const bool altitude_stays_same = fabsf(next_target(2) - target(2)) < config.z_accept_rad;

	float speed_at_target = 0.0f;

	if (target_next_different &&
	    !waypoint_overlap &&
	    has_reached_altitude &&
	    altitude_stays_same
	   ) {
		const float alpha = acosf(Vector2f((target - start_position).xy()).unit_or_zero().dot(
						  Vector2f((target - next_target).xy()).unit_or_zero()));
		const float safe_alpha = constrain(alpha, 0.f, M_PI_F - FLT_EPSILON);
		float accel_tmp = config.max_acc_xy_radius_scale * config.max_acc_xy;
		float max_speed_in_turn = computeMaxSpeedInWaypoint(safe_alpha, accel_tmp, config.xy_accept_rad);
		speed_at_target = min(min(max_speed_in_turn, exit_speed), config.max_speed_xy);
	}

	float start_to_target = (start_position - target).xy().norm();
	float max_speed = computeMaxSpeedFromDistance(config.max_jerk, config.max_acc_xy, start_to_target, speed_at_target);

	return min(config.max_speed_xy, max_speed);
}

/*
 * This function computes the maximum speed XY that can be travelled, given a set of waypoints and vehicle dynamics
 *
 * The first waypoint should be the starting location, and the later waypoints the desired points to be followed.
 *
 * @param waypoints the list of waypoints to be followed, the first of which should be the starting location
 * @param config the vehicle dynamic limits
 *
 * @return the maximum speed at waypoint[0] which allows it to follow the trajectory while respecting the dynamic limits
 */
template <size_t N>
float computeXYSpeedFromWaypoints(const Vector3f waypoints[N], const VehicleDynamicLimits &config)
{
	static_assert(N >= 2, "Need at least 2 points to compute speed");

	float max_speed = 0.f;

	for (size_t j = 0; j < N - 1; j++) {
		size_t i = N - 2 - j;
		max_speed = computeStartXYSpeedFromWaypoints(waypoints[i],
				waypoints[i + 1],
				waypoints[min(i + 2, N - 1)],
				max_speed, config);
	}

	return max_speed;
}

/*
 * Constrain the 3D vector given a maximum XY norm
 * If the XY norm of the 3D vector is larger than the maximum norm, the whole vector
 * is scaled down to respect the constraint.
 * If the maximum norm is small (defined by the "accuracy" parameter),
 * only the XY components are scaled down to avoid affecting
 * Z in case of numerical issues
 */
inline void clampToXYNorm(Vector3f &target, float max_xy_norm, float accuracy = FLT_EPSILON)
{
	const float xynorm = target.xy().norm();
	const float scale_factor = (xynorm > FLT_EPSILON)
				   ? max_xy_norm / xynorm
				   : 1.f;

	if (scale_factor < 1.f) {
		if (max_xy_norm < accuracy && xynorm < accuracy) {
			target.xy() = Vector2f(target) * scale_factor;

		} else {
			target *= scale_factor;
		}
	}
}

/*
 * Constrain the 3D vector given a maximum Z norm
 * If the Z component of the 3D vector is larger than the maximum norm, the whole vector
 * is scaled down to respect the constraint.
 * If the maximum norm is small (defined by the "accuracy parameter),
 * only the Z component is scaled down to avoid affecting
 * XY in case of numerical issues
 */
inline void clampToZNorm(Vector3f &target, float max_z_norm, float accuracy = FLT_EPSILON)
{
	const float znorm = fabs(target(2));
	const float scale_factor = (znorm > FLT_EPSILON)
				   ? max_z_norm / znorm
				   : 1.f;

	if (scale_factor < 1.f) {
		if (max_z_norm < accuracy && znorm < accuracy) {
			target(2) *= scale_factor;

		} else {
			target *= scale_factor;
		}
	}
}

}
}