graceful_controller.cpp

// Copyright (c) 2023 Alberto J. Tudela Roldán
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
 
#include <memory>
#include <mutex>
 
#include "angles/angles.h"
#include "nav2_core/controller_exceptions.hpp"
#include "nav2_util/geometry_utils.hpp"
#include "nav2_util/controller_utils.hpp"
#include "nav2_util/path_utils.hpp"
#include "nav2_graceful_controller/graceful_controller.hpp"
#include "nav2_costmap_2d/costmap_filters/filter_values.hpp"
#include "nav2_ros_common/tf2_factories.hpp"
 
namespace nav2_graceful_controller
{
 
void GracefulController::configure(
  const nav2::LifecycleNode::WeakPtr & parent,
  std::string name, const nav2::TransformBuffer::SharedPtr tf,
  const std::shared_ptr<nav2_costmap_2d::Costmap2DROS> costmap_ros)
{
  nav2::LifecycleNode::SharedPtr node = parent.lock();
  if (!node) {
    throw nav2_core::ControllerException("Unable to lock node!");
  }
 
  costmap_ros_ = costmap_ros;
  tf_buffer_ = tf;
  plugin_name_ = name;
  logger_ = node->get_logger();
 
  // Handles storage and dynamic configuration of parameters.
  // Returns pointer to data current param settings.
  param_handler_ = std::make_unique<ParameterHandler>(
    node, plugin_name_, logger_);
  params_ = param_handler_->getParams();
 
  // Handles the control law to generate the velocity commands
  control_law_ = std::make_unique<SmoothControlLaw>(
    params_->k_phi, params_->k_delta, params_->beta, params_->lambda,
    params_->slowdown_radius, params_->deceleration_max,
    params_->v_linear_min, params_->v_linear_max, params_->v_angular_max);
 
  // Initialize footprint collision checker
  if (params_->use_collision_detection) {
    collision_checker_ = std::make_unique<nav2_costmap_2d::
        FootprintCollisionChecker<nav2_costmap_2d::Costmap2D *>>(costmap_ros_->getCostmap());
  }
 
  double max_valid_cost = costmap_ros_->getUseRadius() ?
    static_cast<double>(nav2_costmap_2d::MAX_NON_OBSTACLE) :
    static_cast<double>(nav2_costmap_2d::INSCRIBED_INFLATED_OBSTACLE);
  if (max_valid_cost - static_cast<double>(params_->obstacle_cost_margin) < 0.0) {
    RCLCPP_WARN(
      logger_, "obstacle_cost_margin (%d) is higher than max cost (%d).",
      params_->obstacle_cost_margin, nav2_costmap_2d::MAX_NON_OBSTACLE);
    throw nav2_core::ControllerException("obstacle_cost_margin is higher than max cost.");
  }
 
  // Publishers
  local_plan_pub_ = node->create_publisher<nav_msgs::msg::Path>("local_plan");
  motion_target_pub_ = node->create_publisher<geometry_msgs::msg::PoseStamped>("motion_target");
  slowdown_pub_ = node->create_publisher<visualization_msgs::msg::Marker>("slowdown");
 
  RCLCPP_INFO(logger_, "Configured Graceful Motion Controller: %s", plugin_name_.c_str());
}
 
void GracefulController::cleanup()
{
  RCLCPP_INFO(
    logger_,
    "Cleaning up controller: %s of type graceful_controller::GracefulController",
    plugin_name_.c_str());
  local_plan_pub_.reset();
  motion_target_pub_.reset();
  slowdown_pub_.reset();
  collision_checker_.reset();
  param_handler_.reset();
  control_law_.reset();
}
 
void GracefulController::activate()
{
  RCLCPP_INFO(
    logger_,
    "Activating controller: %s of type nav2_graceful_controller::GracefulController",
    plugin_name_.c_str());
  local_plan_pub_->on_activate();
  motion_target_pub_->on_activate();
  slowdown_pub_->on_activate();
  param_handler_->activate();
}
 
void GracefulController::deactivate()
{
  RCLCPP_INFO(
    logger_,
    "Deactivating controller: %s of type nav2_graceful_controller::GracefulController",
    plugin_name_.c_str());
  local_plan_pub_->on_deactivate();
  motion_target_pub_->on_deactivate();
  slowdown_pub_->on_deactivate();
  param_handler_->deactivate();
}
 
geometry_msgs::msg::TwistStamped GracefulController::computeVelocityCommands(
  const geometry_msgs::msg::PoseStamped & pose,
  const geometry_msgs::msg::Twist & velocity,
  nav2_core::GoalChecker * goal_checker,
  const nav_msgs::msg::Path & transformed_global_plan,
  const geometry_msgs::msg::PoseStamped & global_goal)
{
  std::lock_guard<std::mutex> param_lock(param_handler_->getMutex());
 
  geometry_msgs::msg::TwistStamped cmd_vel;
  cmd_vel.header = pose.header;
 
  // Transform the plan from costmap's global frame to robot base frame
  nav_msgs::msg::Path transformed_plan;
  if (!nav2_util::transformPathInTargetFrame(
      transformed_global_plan, transformed_plan, *tf_buffer_,
      costmap_ros_->getBaseFrameID(), costmap_ros_->getTransformTolerance()))
  {
    throw nav2_core::ControllerTFError(
    "Unable to transform plan pose into local frame");
  }
 
  // Update the smooth control law with the new params
  control_law_->setCurvatureConstants(
    params_->k_phi, params_->k_delta, params_->beta, params_->lambda);
  control_law_->setSlowdownRadius(params_->slowdown_radius);
  control_law_->setMaxDeceleration(params_->deceleration_max);
  control_law_->setSpeedLimit(params_->v_linear_min, params_->v_linear_max, params_->v_angular_max);
  // Add proper orientations to plan, if needed
  validateOrientations(transformed_plan.poses);
 
  // ControllerServer supplies pose in the local costmap's global frame, so it already
  // represents the transform from the robot base frame to the costmap's global frame.
  geometry_msgs::msg::TransformStamped costmap_transform = nav2_util::poseToTransformStamped(pose,
      costmap_ros_->getBaseFrameID());
 
  // Compute distance to goal as the path's integrated distance to account for path curvatures
  double dist_to_goal = nav2_util::geometry_utils::calculate_path_length(transformed_plan);
 
  // If we've reached the XY goal tolerance, just rotate.
  // Feed the goal checker the GLOBAL-frame plan (same frame as `pose` / `global_goal`), not the
  // base_link-frame `transformed_plan` used for control.
  if (goal_checker->isGoalXYReached(pose.pose, global_goal.pose, velocity,
      transformed_global_plan))
  {
    double angle_to_goal = tf2::getYaw(transformed_plan.poses.back().pose.orientation);
    // Check for collisions between our current pose and goal pose
    size_t num_steps = fabs(angle_to_goal) / params_->in_place_collision_resolution;
    // Need to check at least the end pose
    num_steps = std::max(static_cast<size_t>(1), num_steps);
    bool collision_free = true;
    for (size_t i = 1; i <= num_steps; ++i) {
      double step = static_cast<double>(i) / static_cast<double>(num_steps);
      double yaw = step * angle_to_goal;
      geometry_msgs::msg::PoseStamped next_pose;
      next_pose.header.frame_id = costmap_ros_->getBaseFrameID();
      next_pose.pose.orientation = nav2_util::geometry_utils::orientationAroundZAxis(yaw);
      geometry_msgs::msg::PoseStamped costmap_pose;
      tf2::doTransform(next_pose, costmap_pose, costmap_transform);
      if (params_->use_collision_detection && inCollision(
          costmap_pose.pose.position.x, costmap_pose.pose.position.y,
          tf2::getYaw(costmap_pose.pose.orientation)))
      {
        collision_free = false;
        break;
      }
    }
    // Compute velocity if rotation is possible
    if (collision_free) {
      cmd_vel.twist = rotateToTarget(angle_to_goal);
      return cmd_vel;
    }
    // Else, fall through and see if we should follow control law longer
  }
 
  // Find a valid target pose and its trajectory
  nav_msgs::msg::Path local_plan;
  geometry_msgs::msg::PoseStamped target_pose;
 
  double dist_to_target;
  std::vector<double> target_distances;
  computeDistanceAlongPath(transformed_plan.poses, target_distances);
 
  bool is_first_iteration = true;
  for (int i = transformed_plan.poses.size() - 1; i >= 0; --i) {
    if (is_first_iteration) {
      // Calculate target pose through lookahead interpolation to get most accurate
      // lookahead point, if possible
      dist_to_target = params_->max_lookahead;
      // Interpolate after goal false for graceful controller
      // Requires interpolating the orientation which is not yet implemented
      // Updates dist_to_target for target_pose returned if using the point on the path
      target_pose = nav2_util::getLookAheadPoint(dist_to_target, transformed_plan, false);
      is_first_iteration = false;
    } else {
      // Underlying control law needs a single target pose, which should:
      //  * Be as far away as possible from the robot (for smoothness)
      //  * But no further than the max_lookahed_ distance
      //  * Be feasible to reach in a collision free manner
      dist_to_target = target_distances[i];
      target_pose = transformed_plan.poses[i];
    }
 
    // Compute velocity at this moment if valid target pose is found
    if (
      validateTargetPoseOnApproach(target_pose, dist_to_target, dist_to_goal, local_plan,
        costmap_transform, cmd_vel) ||
      validateTargetPose(target_pose, dist_to_target, local_plan, costmap_transform, cmd_vel))
    {
      // Publish the selected target_pose
      motion_target_pub_->publish(std::make_unique<geometry_msgs::msg::PoseStamped>(target_pose));
      // Publish marker for slowdown radius around motion target for debugging / visualization
      auto slowdown_marker = nav2_graceful_controller::createSlowdownMarker(
        target_pose, params_->slowdown_radius);
      slowdown_pub_->publish(std::make_unique<visualization_msgs::msg::Marker>(slowdown_marker));
      // Publish the local plan
      local_plan.header = transformed_plan.header;
      local_plan_pub_->publish(std::make_unique<nav_msgs::msg::Path>(local_plan));
      // Successfully found velocity command
      return cmd_vel;
    }
  }
 
  throw nav2_core::NoValidControl("Collision detected in trajectory");
}
 
void GracefulController::newPathReceived(const nav_msgs::msg::Path & /*raw_global_path*/)
{
  do_initial_rotation_ = true;
  safe_approach_angle_.reset();
}
 
void GracefulController::setSpeedLimit(
  const double & speed_limit, const bool & percentage)
{
  std::lock_guard<std::mutex> param_lock(param_handler_->getMutex());
 
  if (speed_limit == nav2_costmap_2d::NO_SPEED_LIMIT) {
    params_->v_linear_max = params_->v_linear_max_initial;
    params_->v_angular_max = params_->v_angular_max_initial;
  } else {
    if (percentage) {
      // Speed limit is expressed in % from maximum speed of robot
      params_->v_linear_max = std::max(
        params_->v_linear_max_initial * speed_limit / 100.0, params_->v_linear_min);
      params_->v_angular_max = params_->v_angular_max_initial * speed_limit / 100.0;
    } else {
      // Speed limit is expressed in m/s
      params_->v_linear_max = std::max(speed_limit, params_->v_linear_min);
      // Limit the angular velocity to be proportional to the linear velocity
      params_->v_angular_max = params_->v_angular_max_initial *
        speed_limit / params_->v_linear_max_initial;
    }
  }
}
 
bool GracefulController::validateTargetPose(
  geometry_msgs::msg::PoseStamped & target_pose, double dist_to_target,
  nav_msgs::msg::Path & trajectory, geometry_msgs::msg::TransformStamped & costmap_transform,
  geometry_msgs::msg::TwistStamped & cmd_vel)
{
  // Continue if target_pose is too far away from robot
  if (dist_to_target > params_->max_lookahead) {
    return false;
  }
 
  // Flip the orientation of the motion target if the robot is moving backwards
  bool reversing = false;
  if (params_->allow_backward && target_pose.pose.position.x < 0.0) {
    reversing = true;
    target_pose.pose.orientation = nav2_util::geometry_utils::orientationAroundZAxis(
      tf2::getYaw(target_pose.pose.orientation) + M_PI);
  }
 
  // Actually simulate the path
  double sim_linear_velocity = params_->v_linear_max;
  do {
    control_law_->setSpeedLimit(params_->v_linear_min, sim_linear_velocity, params_->v_angular_max);
    if (simulateTrajectory(target_pose, costmap_transform, trajectory, cmd_vel, reversing)) {
      // Successfully simulated to target_pose
      return true;
    }
    // Reduce velocity and try again for same target_pose
    sim_linear_velocity -= params_->footprint_scaling_step;
  } while (sim_linear_velocity >= params_->footprint_scaling_linear_vel);
 
  // Validation not successful
  return false;
}
 
bool GracefulController::validateTargetPoseOnApproach(
  geometry_msgs::msg::PoseStamped & target_pose, double dist_to_target, double dist_to_goal,
  nav_msgs::msg::Path & trajectory, geometry_msgs::msg::TransformStamped & costmap_transform,
  geometry_msgs::msg::TwistStamped & cmd_vel)
{
  // Not approaching goal with large lookahead and don't evaluate shortcut trajectories
  // when we do not prefer rotating to goal at the end.
  if (dist_to_goal >= params_->max_lookahead || !params_->prefer_final_rotation) {
    return false;
  }
  // Avoid instability and big sweeping turns at the end of paths by
  // ignoring final heading
  double yaw = std::atan2(target_pose.pose.position.y, target_pose.pose.position.x);
  target_pose.pose.orientation =
    nav2_util::geometry_utils::orientationAroundZAxis(yaw);
 
  if (validateTargetPose(target_pose, dist_to_target, trajectory, costmap_transform, cmd_vel)) {
    // Determine the maximum valid cost based on robot footprint type
    double max_valid_cost =
      costmap_ros_->getUseRadius() ? static_cast<double>(nav2_costmap_2d::MAX_NON_OBSTACLE) :
      static_cast<double>(nav2_costmap_2d::INSCRIBED_INFLATED_OBSTACLE);
 
    // Check if the final rotation path is risky
    double safety_threshold = max_valid_cost - static_cast<double>(params_->obstacle_cost_margin);
    if (getMaxCost(trajectory, costmap_transform) >= safety_threshold) {
      // Try to find a better approach by searching spiral curves
      findBestApproachTrajectory(
            target_pose, dist_to_target, costmap_transform, max_valid_cost, trajectory, cmd_vel);
    }
    return true;
  }
  return false;
}
 
bool GracefulController::simulateTrajectory(
  const geometry_msgs::msg::PoseStamped & motion_target,
  const geometry_msgs::msg::TransformStamped & costmap_transform,
  nav_msgs::msg::Path & trajectory,
  geometry_msgs::msg::TwistStamped & cmd_vel,
  bool backward)
{
  trajectory.poses.clear();
 
  // First pose is robot current pose
  geometry_msgs::msg::PoseStamped next_pose;
  next_pose.header.frame_id = costmap_ros_->getBaseFrameID();
  next_pose.pose.orientation.w = 1.0;
 
  // Should we simulate rotation initially?
  bool sim_initial_rotation = do_initial_rotation_ && params_->initial_rotation;
  double angle_to_target =
    std::atan2(motion_target.pose.position.y, motion_target.pose.position.x);
  if (fabs(angle_to_target) < params_->initial_rotation_tolerance) {
    sim_initial_rotation = false;
    do_initial_rotation_ = false;
  }
 
  double distance = std::numeric_limits<double>::max();
  double resolution = costmap_ros_->getCostmap()->getResolution();
  double dt = (params_->v_linear_max > 0.0) ? resolution / params_->v_linear_max : 0.0;
 
  // Set max iter to avoid infinite loop
  unsigned int max_iter = 3 *
    std::hypot(motion_target.pose.position.x, motion_target.pose.position.y) / resolution;
 
  // Generate path
  do{
    if (sim_initial_rotation) {
      // Compute rotation velocity
      double next_pose_yaw = tf2::getYaw(next_pose.pose.orientation);
      auto cmd = rotateToTarget(angle_to_target - next_pose_yaw);
 
      // If this is first iteration, this is our current target velocity
      if (trajectory.poses.empty()) {cmd_vel.twist = cmd;}
 
      // Are we done simulating initial rotation?
      if (fabs(angle_to_target - next_pose_yaw) < params_->initial_rotation_tolerance) {
        sim_initial_rotation = false;
      }
 
      // Forward simulate rotation command
      next_pose_yaw += cmd_vel.twist.angular.z * dt;
      next_pose.pose.orientation = nav2_util::geometry_utils::orientationAroundZAxis(next_pose_yaw);
    } else {
      // If this is first iteration, this is our current target velocity
      if (trajectory.poses.empty()) {
        cmd_vel.twist = control_law_->calculateRegularVelocity(
          motion_target.pose, next_pose.pose, backward);
      }
 
      // Apply velocities to calculate next pose
      next_pose.pose = control_law_->calculateNextPose(
        dt, motion_target.pose, next_pose.pose, backward);
    }
 
    // Add the pose to the trajectory for visualization
    trajectory.poses.push_back(next_pose);
 
    // Compute footprint scaling
    double footprint_scaling = 1.0;
    if (cmd_vel.twist.linear.x > params_->footprint_scaling_linear_vel) {
      // Scaling = (vel_x - scaling_vel_x) / (max_vel_x - scaling_vel_x)
      double ratio = params_->v_linear_max - params_->footprint_scaling_linear_vel;
      // Avoid divide by zero
      if (ratio > 0) {
        ratio = (cmd_vel.twist.linear.x - params_->footprint_scaling_linear_vel) / ratio;
        footprint_scaling += ratio * params_->footprint_scaling_factor;
      }
    }
 
    // Check for collision
    geometry_msgs::msg::PoseStamped global_pose;
    tf2::doTransform(next_pose, global_pose, costmap_transform);
    if (params_->use_collision_detection && inCollision(
        global_pose.pose.position.x, global_pose.pose.position.y,
        tf2::getYaw(global_pose.pose.orientation), footprint_scaling))
    {
      return false;
    }
 
    // Check if we reach the goal
    distance = nav2_util::geometry_utils::euclidean_distance(motion_target.pose, next_pose.pose);
  }while(distance > resolution && trajectory.poses.size() < max_iter);
 
  return true;
}
 
geometry_msgs::msg::Twist GracefulController::rotateToTarget(double angle_to_target)
{
  geometry_msgs::msg::Twist vel;
  vel.linear.x = 0.0;
  vel.angular.z = params_->rotation_scaling_factor * angle_to_target * params_->v_angular_max;
  vel.angular.z = std::copysign(1.0, vel.angular.z) * std::max(
    abs(vel.angular.z),
    params_->v_angular_min_in_place);
  return vel;
}
 
double GracefulController::getMaxCost(
  const nav_msgs::msg::Path & path, geometry_msgs::msg::TransformStamped & costmap_transform)
{
  double max_cost = 0.0;
 
  for (const auto & pose : path.poses) {
    geometry_msgs::msg::PoseStamped costmap_pose;
    tf2::doTransform(pose, costmap_pose, costmap_transform);
    unsigned int mx, my;
    if (costmap_ros_->getCostmap()->worldToMap(costmap_pose.pose.position.x,
        costmap_pose.pose.position.y, mx, my))
    {
      max_cost = std::max(max_cost, collision_checker_->pointCost(mx, my));
    }
  }
 
  return max_cost;
}
 
bool GracefulController::inCollision(
  const double & x, const double & y, const double & theta,
  double inflation_scale)
{
  unsigned int mx, my;
  if (!costmap_ros_->getCostmap()->worldToMap(x, y, mx, my)) {
    RCLCPP_WARN(
      logger_, "The path is not in the costmap. Cannot check for collisions. "
      "Proceed at your own risk, slow the robot, or increase your costmap size.");
    return false;
  }
 
  if (inflation_scale < 1.0) {
    RCLCPP_WARN(logger_, "Inflation ratio cannot be less than 1.0");
    throw nav2_core::NoValidControl("Inflation ratio less than 1.0");
  }
 
  // Calculate the cost of the footprint at the robot's current position depending
  // on the shape of the footprint
  bool is_tracking_unknown =
    costmap_ros_->getLayeredCostmap()->isTrackingUnknown();
  bool consider_footprint = !costmap_ros_->getUseRadius();
 
  double footprint_cost;
  if (consider_footprint) {
    std::vector<geometry_msgs::msg::Point> spec = costmap_ros_->getRobotFootprint();
    if (spec.size() > 3) {
      for (auto & point : spec) {
        point.x *= inflation_scale;
        point.y *= inflation_scale;
      }
    }
    footprint_cost = collision_checker_->footprintCostAtPose(x, y, theta, spec);
  } else {
    footprint_cost = collision_checker_->pointCost(mx, my);
  }
 
  switch (static_cast<unsigned char>(footprint_cost)) {
    case (nav2_costmap_2d::LETHAL_OBSTACLE):
      return true;
    case (nav2_costmap_2d::INSCRIBED_INFLATED_OBSTACLE):
      return consider_footprint ? false : true;
    case (nav2_costmap_2d::NO_INFORMATION):
      return is_tracking_unknown ? false : true;
  }
 
  return false;
}
 
void GracefulController::computeDistanceAlongPath(
  const std::vector<geometry_msgs::msg::PoseStamped> & poses,
  std::vector<double> & distances)
{
  distances.resize(poses.size());
  // Do the first pose from robot
  double d = std::hypot(poses[0].pose.position.x, poses[0].pose.position.y);
  distances[0] = d;
  // Compute remaining poses
  for (size_t i = 1; i < poses.size(); ++i) {
    d += nav2_util::geometry_utils::euclidean_distance(poses[i - 1].pose, poses[i].pose);
    distances[i] = d;
  }
}
 
void GracefulController::validateOrientations(
  std::vector<geometry_msgs::msg::PoseStamped> & path)
{
  // We never change the orientation of the first & last pose
  // So we need at least three poses to do anything here
  if (path.size() < 3) {return;}
 
  // Check if we actually need to add orientations
  double initial_yaw = tf2::getYaw(path[1].pose.orientation);
  for (size_t i = 2; i < path.size() - 1; ++i) {
    double this_yaw = tf2::getYaw(path[i].pose.orientation);
    if (angles::shortest_angular_distance(this_yaw, initial_yaw) > 1e-6) {return;}
  }
 
  // For each pose, point at the next one
  // NOTE: control loop will handle reversing logic
  for (size_t i = 0; i < path.size() - 1; ++i) {
    // Get relative yaw angle
    double dx = path[i + 1].pose.position.x - path[i].pose.position.x;
    double dy = path[i + 1].pose.position.y - path[i].pose.position.y;
    double yaw = std::atan2(dy, dx);
    path[i].pose.orientation = nav2_util::geometry_utils::orientationAroundZAxis(yaw);
  }
}
 
bool GracefulController::findBestApproachTrajectory(
  geometry_msgs::msg::PoseStamped & target_pose, double dist_to_target,
  geometry_msgs::msg::TransformStamped & costmap_transform, double safety_cost,
  nav_msgs::msg::Path & best_trajectory, geometry_msgs::msg::TwistStamped & best_cmd_vel)
{
  bool found_valid = false;
  double best_eta = std::numeric_limits<double>::max();
 
  for (int i = 0; i < 2 * M_PI / params_->final_rotation_search_step; ++i) {
    double angle = static_cast<double>(i) * params_->final_rotation_search_step;
    // Prioritize previously selected approach angles
    if (safe_approach_angle_.has_value()) {
      angle += safe_approach_angle_.value();
    }
 
    // Create candidate pose
    auto candidate_pose = target_pose;
    candidate_pose.pose.orientation = nav2_util::geometry_utils::orientationAroundZAxis(angle);
 
    nav_msgs::msg::Path candidate_path = best_trajectory;
    geometry_msgs::msg::TwistStamped candidate_cmd_vel = best_cmd_vel;
 
    // Validate the candidate
    if (validateTargetPose(
          candidate_pose, dist_to_target, candidate_path, costmap_transform,
          candidate_cmd_vel))
    {
      double candidate_cost = getMaxCost(candidate_path, costmap_transform);
 
      bool reversing = false;
      if (params_->allow_backward && target_pose.pose.position.x < 0.0) {
        reversing = true;
      }
      // Calculate ETA
      double eta = 0.0;
      for (size_t j = 1; j < candidate_path.poses.size(); ++j) {
        auto current_pose = candidate_path.poses[j - 1];
        auto next_pose = candidate_path.poses[j];
        auto cmd = control_law_->calculateRegularVelocity(candidate_pose.pose, current_pose.pose,
          reversing);
        double speed = std::abs(cmd.linear.x);
        // Avoid division by zero
        speed = std::max(speed, 1e-3);
        double step_dist = nav2_util::geometry_utils::euclidean_distance(
          current_pose.pose, next_pose.pose);
        double step_time = step_dist / speed;
        eta += step_time;
      }
 
      // Selection logic: Pick the fastest among the safe ones
      if (eta < best_eta) {
        best_eta = eta;
        if (candidate_cost < safety_cost) {
          best_trajectory = candidate_path;
          best_cmd_vel = candidate_cmd_vel;
          target_pose = candidate_pose;
          found_valid = true;
          // Reuse known safe approach angle if still valid
          if (safe_approach_angle_.value_or(1e3 /*Never in (-PI, PI]*/) == angle) {
            break;
          }
          safe_approach_angle_ = angle;
        }
      }
    }
  }
 
  return found_valid;
}
 
}  // namespace nav2_graceful_controller
 
// Register this controller as a nav2_core plugin
PLUGINLIB_EXPORT_CLASS(
  nav2_graceful_controller::GracefulController,
  nav2_core::Controller)