`/follow_path`#

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/follow_path Quick Facts

Category: 🧭 Navigation
Message type: nav2_msgs/action/FollowPath

Nav2 Action Server implemented by the nav2_controller package. Executes a given Path using the Controller (Local Planner).

Quick snippets#

Send a goal from the command-line#

$ ros2 action send_goal /follow_path nav2_msgs/action/FollowPath # press Tab to complete the message prototype

How to use in your code#

Call the action from a Python script#

#!/usr/bin/env python

import rclpy
from rclpy.action import ActionClient
from rclpy.node import Node

from nav2_msgs.action import FollowPath

class FollowPathActionClient(Node):

    def __init__(self):
        super().__init__('follow_path_client')
        self._action_client = ActionClient(self, FollowPath, '/follow_path')

    def send_goal(self, a, b):
        goal_msg = FollowPath.Goal()

        # TODO: adapt to the action's parameters
        # check https://docs.ros2.org/latest/api/nav2_msgs/action/FollowPath.html
        # for the possible goal parameters
        # goal_msg.a = a
        # goal_msg.b = b

        self._action_client.wait_for_server()

        return self._action_client.send_goal_async(goal_msg)

if __name__ == '__main__':
    rclpy.init(args=args)

    action_client = FollowPathActionClient()

    # TODO: adapt to your action's parameters
    future = action_client.send_goal(a, b)

    rclpy.spin_until_future_complete(action_client, future)

    rclpy.shutdown()

Call the action from a C++ program#

#include <functional>
#include <future>
#include <memory>
#include <string>
#include <sstream>
#include <chrono>

#include "nav2_msgs/action/follow_path.hpp"

#include "rclcpp/rclcpp.hpp"
#include "rclcpp_action/rclcpp_action.hpp"
#include "rclcpp_components/register_node_macro.hpp"

using namespace std::chrono_literals;
using namespace std;

class FollowPathActionClient : public rclcpp::Node
{
public:
  using FollowPath = nav2_msgs::action::FollowPath;
  using GoalHandleFollowPath = rclcpp_action::ClientGoalHandle<FollowPath>;

  explicit FollowPathActionClient(const rclcpp::NodeOptions & options)
  : Node("follow_path_action_client", options)
  {
    this->client_ptr_ = rclcpp_action::create_client<FollowPath>(
            this,
            "/follow_path");

    this->timer_ = this->create_wall_timer(
            500ms,
            bind(&FollowPathActionClient::send_goal, this));
  }

  void send_goal()
  {
    using namespace std::placeholders;

    this->timer_->cancel();

    if (!this->client_ptr_->wait_for_action_server()) {
      RCLCPP_ERROR(this->get_logger(), "Action server not available after waiting");
      rclcpp::shutdown();
    }

    auto goal_msg = FollowPath::Goal();

    // check https://docs.ros2.org/latest/api/nav2_msgs/action/FollowPath.html
    // for the possible goal parameters
    // goal_msg.... = ...;

    RCLCPP_INFO(this->get_logger(), "Sending goal");

    auto send_goal_options = rclcpp_action::Client<FollowPath>::SendGoalOptions();

    send_goal_options.goal_response_callback =
        bind(&FollowPathActionClient::goal_response_callback, this, _1);

    send_goal_options.feedback_callback =
        bind(&FollowPathActionClient::feedback_callback, this, _1, _2);

    send_goal_options.result_callback =
        bind(&FollowPathActionClient::result_callback, this, _1);


    this->client_ptr_->async_send_goal(goal_msg, send_goal_options);
  }

private:
  rclcpp_action::Client<FollowPath>::SharedPtr client_ptr_;
  rclcpp::TimerBase::SharedPtr timer_;

  void goal_response_callback(const GoalHandleFollowPath::SharedPtr & goal_handle)
  {
    if (!goal_handle) {
      RCLCPP_ERROR(this->get_logger(), "Goal was rejected by server");
    } else {
      RCLCPP_INFO(this->get_logger(), "Goal accepted by server, waiting for result");
    }
  }

  void feedback_callback(
      GoalHandleFollowPath::SharedPtr,
      const shared_ptr<const FollowPath::Feedback> feedback)
  {
    stringstream ss;
    ss << "Next number in sequence received: ";
    for (auto number : feedback->partial_sequence) {
      ss << number << " ";
    }
    RCLCPP_INFO(this->get_logger(), ss.str().c_str());
  }

  void result_callback(const GoalHandleFollowPath::WrappedResult & result)
  {
    switch (result.code) {
      case rclcpp_action::ResultCode::SUCCEEDED:
          break;
      case rclcpp_action::ResultCode::ABORTED:
          RCLCPP_ERROR(this->get_logger(), "Goal was aborted");
          return;
      case rclcpp_action::ResultCode::CANCELED:
          RCLCPP_ERROR(this->get_logger(), "Goal was canceled");
          return;
      default:
          RCLCPP_ERROR(this->get_logger(), "Unknown result code");
          return;
    }
    stringstream ss;
    ss << "Result received: ";
    for (auto number : result.result->sequence) {
      ss << number << " ";
    }
    RCLCPP_INFO(this->get_logger(), ss.str().c_str());
    rclcpp::shutdown();
  }
};  // class FollowPathActionClient


RCLCPP_COMPONENTS_REGISTER_NODE(FollowPathActionClient)

/follow_path#

Quick snippets#

How to use in your code#

`/follow_path`#