Sachin Kumar Follow Making Robots Smarter

Create ROS2 pkg to build c++ and python files

The Robot Operating System (ROS) is a set of software libraries and tools for building robot applications. From drivers to state-of-the-art algorithms, and with powerful developer tools, ROS has what you need for your next robotics project. And it’s all open source.

ROS2 is the next version of ROS which provides more features and deals with limitations from the previous version. ROS2 provides three types of build-depends as ament_cmake, ament_python, and cmake. Recently I was working on a ROS2 project in which I was using ROS2 python to create the node. In this, I need to create a custom ROS2 msg-type. I searched for the tutorials and documents to create custom msgs in the ros2 pkg with build type ament_python. But I didn’t find any way to build a custom msg in the python build type pkg. So, to solve this problem, I created a new pkg in ros2 with build_type ament_cmake to build the custom messages. That’s how I solved the problem. But that is not all. This is not how it should work. We can need to find a way to build the msgs, c++ files, and even python scripts. Luckily, I found this and will share the process.

Create a ros2 pkg inside your colcon_ws

$ ros2 create pkg my_ros2_pkg --build-type --ament-cmake

Build the pkg

$ colcon build

Create a custom msg

Make a folder msg in the ros2 pkg and add file Num.msg

int64 num

Create a Publisher in C++ in src

make a file ros2_publisher.cpp in the src folder

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

#include "rclcpp/rclcpp.hpp"
#include "std_msgs/msg/string.hpp"
#include "my_ros2_pkg/msg/num.hpp"

using namespace std::chrono_literals;

class Ros2Publisher : public rclcpp::Node
{
	public:
		Ros2Publisher()
			: Node("ros2_publisher"), count_(0)
		{
			publisher_ = this->create_publisher<std_msgs::msg::String>("topic", 10);
			num_publisher_ = this->create_publisher<my_ros2_pkg::msg::Num>("num", 10);
			timer_ = this->create_wall_timer(
					500ms, std::bind(&Ros2Publisher::timer_callback, this));
		}

	private:
		void timer_callback()
		{
			auto message = std_msgs::msg::String();
			message.data = "Hello, world! " + std::to_string(count_++);
			auto num_msg = my_ros2_pkg::msg::Num();
			num_msg.num = 100;
			RCLCPP_INFO(this->get_logger(), "Publishing: '%s'", message.data.c_str());
			publisher_->publish(message);
			num_publisher_->publish(num_msg);
		}

		rclcpp::TimerBase::SharedPtr timer_;
		rclcpp::Publisher<std_msgs::msg::String>::SharedPtr publisher_;
		rclcpp::Publisher<my_ros2_pkg::msg::Num>::SharedPtr num_publisher_;
		size_t count_;
};

int main(int argc, char * argv[])
{
	rclcpp::init(argc, argv);
	rclcpp::spin(std::make_shared<Ros2Publisher>());
	rclcpp::shutdown();
	return 0;
}

Create a subscriber in Python in scripts

create a folder named same as pkg e.g. my_ros2_pkg and inside this folder create a file init.py and add the files you want to use as modules

make a file ros2_subscriber.py in the folder scripts

#!/usr/bin/env python3

import rclpy
from rclpy.node import Node

from std_msgs.msg import String


class Ros2Subscriber(Node):
    def __init__(self):
        super().__init__('ros2_subscriber')
        self.subscription = self.create_subscription(
            String,
            'topic',
            self.listener_callback,
            10)
        self.subscription

    def listener_callback(self, msg):
        self.get_logger().info('I heard: "%s"' % msg.data)


def main(args=None):
    rclpy.init(args=args)
    ros2_subscriber = Ros2Subscriber()

    rclpy.spin(ros2_subscriber)

    ros2_subscriber.destroy_node()

    rclpy.shutdown()


if __name__ == '__main__':
    main()

Modify package.xml

<?xml version="1.0"?>
<?xml-model href="http://download.ros.org/schema/package_format3.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
<package format="3">
	<name>my_ros2_pkg</name>
	<version>0.0.0</version>
	<description>TODO: Package description</description>
	<maintainer email="sachinkum123567@gmail.com">hunter</maintainer>
	<license>TODO: License declaration</license>

	<buildtool_depend>ament_cmake</buildtool_depend>
	<buildtool_depend>ament_cmake_python</buildtool_depend>

	<depend>rclcpp</depend>
	<depend>rclpy</depend>


	<test_depend>ament_lint_auto</test_depend>
	<test_depend>ament_lint_common</test_depend>

	<build_depend>rosidl_default_generators</build_depend>

	<exec_depend>rosidl_default_runtime</exec_depend>

	<member_of_group>rosidl_interface_packages</member_of_group>


	<export>
		<build_type>ament_cmake</build_type>


	</export>
</package>

Modify CMakeList.xml

cmake_minimum_required(VERSION 3.5)
project(my_ros2_pkg)

# Default to C99
if(NOT CMAKE_C_STANDARD)
  set(CMAKE_C_STANDARD 99)
endif()

# 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(ament_cmake_python REQUIRED)
find_package(rclcpp REQUIRED)
find_package(rclcpp REQUIRED)
find_package(my_ros2_pkg REQUIRED)

rosidl_generate_interfaces(${PROJECT_NAME}
  "msg/Num.msg"
 )

# uncomment the following section in order to fill in
# further dependencies manually.
# find_package(<dependency> REQUIRED)

# Include cpp "include" directory
include_directories(include)

# Create Cpp executable
add_executable(ros2_publisher src/ros2_publisher.cpp)
ament_target_dependencies(ros2_publisher rclcpp my_ros2_pkg)

# Install Cpp executables
install(TARGETS
	ros2_publisher
	DESTINATION lib/${PROJECT_NAME}
	)

# Install Python modules
ament_python_install_package(${PROJECT_NAME})

# Install Python executables
install(PROGRAMS
	scripts/ros2_subscriber.py
	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()

Test ros2 publisher node, subscriber node and custom msg

Publisher

$ ros2 run my_ros2_pkg ros2_publisher 
[INFO] [1614431609.679963831] [ros2_publisher]: Publishing: 'Hello, world! 0'
[INFO] [1614431610.180021664] [ros2_publisher]: Publishing: 'Hello, world! 1'
[INFO] [1614431610.679854568] [ros2_publisher]: Publishing: 'Hello, world! 2'
[INFO] [1614431611.179983858] [ros2_publisher]: Publishing: 'Hello, world! 3'
[INFO] [1614431611.679797258] [ros2_publisher]: Publishing: 'Hello, world! 4'
[INFO] [1614431612.179901033] [ros2_publisher]: Publishing: 'Hello, world! 5'
[INFO] [1614431612.679918919] [ros2_publisher]: Publishing: 'Hello, world! 6'
[INFO] [1614431613.179945430] [ros2_publisher]: Publishing: 'Hello, world! 7'
[INFO] [1614431613.679860337] [ros2_publisher]: Publishing: 'Hello, world! 8'
[INFO] [1614431614.179820863] [ros2_publisher]: Publishing: 'Hello, world! 9'
[INFO] [1614431614.679830158] [ros2_publisher]: Publishing: 'Hello, world! 10'
[INFO] [1614431615.179736326] [ros2_publisher]: Publishing: 'Hello, world! 11'
[INFO] [1614431615.679892254] [ros2_publisher]: Publishing: 'Hello, world! 12'
[INFO] [1614431616.179879969] [ros2_publisher]: Publishing: 'Hello, world! 13'
[INFO] [1614431616.679818267] [ros2_publisher]: Publishing: 'Hello, world! 14'
^C[INFO] [1614431617.169909878] [rclcpp]: signal_handler(signal_value=2)

Subscriber

$ ros2 run my_ros2_pkg ros2_subscriber.py 
[INFO] [1614431612.224064221] [ros2_subscriber]: I heard: "Hello, world! 5"
[INFO] [1614431612.683359069] [ros2_subscriber]: I heard: "Hello, world! 6"
[INFO] [1614431613.183585038] [ros2_subscriber]: I heard: "Hello, world! 7"
[INFO] [1614431613.682893150] [ros2_subscriber]: I heard: "Hello, world! 8"
[INFO] [1614431614.182802153] [ros2_subscriber]: I heard: "Hello, world! 9"
[INFO] [1614431614.681286602] [ros2_subscriber]: I heard: "Hello, world! 10"
[INFO] [1614431615.180778766] [ros2_subscriber]: I heard: "Hello, world! 11"
[INFO] [1614431615.683260114] [ros2_subscriber]: I heard: "Hello, world! 12"
[INFO] [1614431616.183141831] [ros2_subscriber]: I heard: "Hello, world! 13"
[INFO] [1614431616.683013687] [ros2_subscriber]: I heard: "Hello, world! 14"

ROS2 custom msg

$ ros2 topic echo /num
num: 100
---
num: 100
---
num: 100
---
num: 100
---
num: 100
---
num: 100
---
num: 100
---

That’s all! For ros2 pkg that can build custom msgs and srvs and even build C++ file with includes and Python scripts with modules. ❤️

27 Feb 2021

ros2

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Create ROS2 pkg to build c++ and python files