[ROS2] Hello World

February 21, 2024 3 분 소요

Intro

C++ 언어로 간단한 구조의 토픽(Topic) 퍼블리셔(Publisher)와 서브스크라이버(Subscriber)를 작성하고 동작시켜보자.

1. Package Directory

📦my_first_ros_rclcpp_pkg
 ┣ 📂include
 ┃ ┗ 📂my_first_ros_rclcpp_pkg
 ┣ 📂src
 ┃ ┣ 📜helloworld_publisher.cpp
 ┃ ┗ 📜helloworld_subscriber.cpp
 ┣ 📜CMakeLists.txt
 ┗ 📜package.xml

2. Code

2.1. CMakeLists.txt

# Default to C++14
if(NOT CMAKE_CXX_STANDARD)
  set(CMAKE_CXX_STANDARD 14)
endif()

if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
  add_compile_options(-Wall -Wextra -Wpedantic)
endif()

# find dependencies
find_package(ament_cmake REQUIRED)
find_package(rclcpp REQUIRED)
find_package(std_msgs REQUIRED)

# Build
add_executable(helloworld_publisher src/helloworld_publisher.cpp)
ament_target_dependencies(helloworld_publisher rclcpp std_msgs)

add_executable(helloworld_subscriber src/helloworld_subscriber.cpp)
ament_target_dependencies(helloworld_subscriber rclcpp std_msgs)

# Install
install(TARGETS
  helloworld_publisher
  helloworld_subscriber
  DESTINATION lib/${PROJECT_NAME})

if(BUILD_TESTING)
  find_package(ament_lint_auto REQUIRED)
  # the following line skips the linter which checks for copyrights
  # uncomment the line when a copyright and license is not present in all source files
  #set(ament_cmake_copyright_FOUND TRUE)
  # the following line skips cpplint (only works in a git repo)
  # uncomment the line when this package is not in a git repo
  #set(ament_cmake_cpplint_FOUND TRUE)
  ament_lint_auto_find_test_dependencies()
endif()

ament_package()

기본 패키지의 CMakeLists.txt 파일에서 아래의 부분을 추가한 것이다.

# Build
add_executable(helloworld_publisher src/helloworld_publisher.cpp)
ament_target_dependencies(helloworld_publisher rclcpp std_msgs)

add_executable(helloworld_subscriber src/helloworld_subscriber.cpp)
ament_target_dependencies(helloworld_subscriber rclcpp std_msgs)

# Install
install(TARGETS
  helloworld_publisher
  helloworld_subscriber
  DESTINATION lib/${PROJECT_NAME})

내용은 다음과 같이 정리할 수 있다.

src/helloworld_publisher.cpp을 컴파일하여 helloworld_publisher 실행파일 생성
src/helloworld_subscriber.cpp을 컴파일하여 helloworld_subscriber 실행파일 생성
실행파일 helloworld_publish과 helloworld_subscriber 은 패키지 rclcpp 과 std_msgs에 의존성을 가짐
실행파일 helloworld_publish과 helloworld_subscriber 은 작업공간(workspace)의 디렉토리 lib/${PROJECT_NAME} 에 저장

빌드를 완료해준 후에 디렉터리를 확인해보면 다음과 같음을 확인할 수 있다.

2.2. helloworld_publisher.cpp

/ Copyright 2016 Open Source Robotics Foundation, Inc.
//
// 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 <chrono>
#include <functional>
#include <memory>
#include <string>

#include "rclcpp/rclcpp.hpp"
#include "std_msgs/msg/string.hpp"

#include <iostream>

using namespace std::chrono_literals;
using namespace std;

class HelloworldPublisher : public rclcpp::Node
{
public:
  HelloworldPublisher()
  : Node("helloworld_publisher"), count_(0)
  {
    auto qos_profile = rclcpp::QoS(rclcpp::KeepLast(10));
    helloworld_publisher_ = this->create_publisher<std_msgs::msg::String>(
      "helloworld", qos_profile);
    timer_ = this->create_wall_timer(
      1s, std::bind(&HelloworldPublisher::publish_helloworld_msg, this));
  }

private:
  void publish_helloworld_msg()
  {
    auto msg = std_msgs::msg::String();
    msg.data = "Hello World: " + std::to_string(count_++);
    RCLCPP_INFO(this->get_logger(), "Published message: '%s'", msg.data.c_str());
    helloworld_publisher_->publish(msg);
  }
  rclcpp::TimerBase::SharedPtr timer_;
  rclcpp::Publisher<std_msgs::msg::String>::SharedPtr helloworld_publisher_;
  size_t count_;
};


int main(int argc, char * argv[])
{
  cout << "PUB: rclcpp::init(argc, argv);\n";
  rclcpp::init(argc, argv);
  auto node = std::make_shared<HelloworldPublisher>();
  cout << "PUB: rclcpp::spin(node);\n";
  rclcpp::spin(node);
  cout << "PUB: rclcpp::shutdown();\n";
  rclcpp::shutdown();
  
  return 0;
}

퍼블리셔 노드의 cpp 내용을 정리하면 다음과 같다.

해당 노드의 메인 클래스는 rclcpp의 Node 클래스를 상속
```
  class HelloworldPublisher : public rclcpp::Node
```
퍼블리셔 의 Qos에서 KeepLast 형태로 depth을 10으로 설정
```
  auto qos_profile = rclcpp::QoS(rclcpp::KeepLast(10));
```
Node 클래스의 create_publisher 함수를 이용하여 퍼블리셔 설정. 매개변수의 토픽 메시지 타입은 String, 토픽 이름은 "helloworld", QoS는 qos_profile
```
  helloworld_publisher_ = this->create_publisher<std_msgs::msg::String>(
    "helloworld", qos_profile);
```

Node 클래스의 create_wall_timer 함수를 이용해 콜백 함수 실행. 주기는 1s.

  timer_ = this->create_wall_timer(
    1s, std::bind(&HelloworldPublisher::publish_helloworld_msg, this));

콜백 함수

  void publish_helloworld_msg()
{
  auto msg = std_msgs::msg::String();
  msg.data = "Hello World: " + std::to_string(count_++);
  RCLCPP_INFO(this->get_logger(), "Published message: '%s'", msg.data.c_str());
  helloworld_publisher_->publish(msg);
}

2.3. helloworld_subscriber.cpp

서브스크라이브 함수도 퍼블리시 함수와 비슷하다.

// Copyright 2016 Open Source Robotics Foundation, Inc.
//
// 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 <functional>
#include <memory>

#include "rclcpp/rclcpp.hpp"
#include "std_msgs/msg/string.hpp"

#include <iostream>

using std::placeholders::_1;
using namespace std;

class HelloworldSubscriber : public rclcpp::Node
{
public:
  HelloworldSubscriber()
  : Node("Helloworld_subscriber")
  {
    auto qos_profile = rclcpp::QoS(rclcpp::KeepLast(10));
    helloworld_subscriber_ = this->create_subscription<std_msgs::msg::String>(
      "helloworld",
      qos_profile,
      std::bind(&HelloworldSubscriber::subscribe_topic_message, this, _1));
  }

private:
  void subscribe_topic_message(const std_msgs::msg::String::SharedPtr msg) const
  {
    RCLCPP_INFO(this->get_logger(), "Received message: '%s'", msg->data.c_str());
  }
  rclcpp::Subscription<std_msgs::msg::String>::SharedPtr helloworld_subscriber_;
};


int main(int argc, char * argv[])
{
  cout << "SUB: rclcpp::init(argc, argv);\n";
  rclcpp::init(argc, argv);
  auto node = std::make_shared<HelloworldSubscriber>();
  cout << "SUB: rclcpp::spin(node);\n";
  rclcpp::spin(node);
  cout << "SUB: rclcpp::shutdown();\n";
  rclcpp::shutdown();
  return 0;
}

3. Run

빌드를 진행한 뒤에 실행을 시켜보면 다음과 같다. 함수 호출 순서를 확인해 보기 위해서 cout 부분을 추가하였다.

rqt_graph 를 통해서 노드와 토픽을 살펴보자.

Reference

ROS 2로 시작하는 로봇 프로그래밍 | 표윤석

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Kim Jyeonghyeon

[ROS2] Hello World

Intro

1. Package Directory

2. Code

2.1. CMakeLists.txt

2.2. helloworld_publisher.cpp

2.3. helloworld_subscriber.cpp

3. Run

Reference

공유하기

참고

[ROS2] Issues

[ROS2] 빌드 설정 파일(CMakeLists.txt)

[ROS2] Modeling Packages

[ROS2] xacro