[ROS2 시작하기 - 6] Parameter

1. ROS2 Parameter

• Settings for your nodes, value set at run time
• A Parameter is specific to a node
• ROS2 Parameter types
  • boolean, int, double, string, lists, …

2. Declare your parameter

number_publisher.cpp

      

      

      

    
    

      <cpp />
    
#include "rclcpp/rclcpp.hpp"
#include "example_interfaces/msg/int64.hpp"

class NumberPublisherNode : public rclcpp::Node
{
public:
    NumberPublisherNode() : Node("number_publisher"), number_(2)
    {
				// add this line
        this->declare_parameter("name");
        
        number_publisher_ = this->create_publisher<example_interfaces::msg::Int64>("number", 10);
        number_timer_ = this->create_wall_timer(std::chrono::seconds(1),
                                                std::bind(&NumberPublisherNode::publishNumber, this));
        RCLCPP_INFO(this->get_logger(), "Number publisher has been started.");
    }

private:
    void publishNumber()
    {
        auto msg = example_interfaces::msg::Int64();
        msg.data = number_;
        number_publisher_->publish(msg);
    }

    int number_;
    rclcpp::Publisher<example_interfaces::msg::Int64>::SharedPtr number_publisher_;
    rclcpp::TimerBase::SharedPtr number_timer_;
};

int main(int argc, char **argv)
{
    rclcpp::init(argc, argv);
    auto node = std::make_shared<NumberPublisherNode>();
    rclcpp::spin(node);
    rclcpp::shutdown();
    return 0;
}

Better code

      

      

      

    
    

      <cpp />
    
#include "rclcpp/rclcpp.hpp"
#include "example_interfaces/msg/int64.hpp"

class NumberPublisherNode : public rclcpp::Node
{
public:
    NumberPublisherNode() : Node("number_publisher")
    {
        this->declare_parameter("number_to_publish", 2);
        this->declare_parameter("publish_frequency", 1.0);

        number_ = this->get_parameter("number_to_publish").as_int();
        double publish_frequency = this->get_parameter("publish_frequency").as_double();

        number_publisher_ = this->create_publisher<example_interfaces::msg::Int64>("number", 10);
        number_timer_ = this->create_wall_timer(std::chrono::milliseconds((int) (1000.0 / publish_frequency)),
                                                std::bind(&NumberPublisherNode::publishNumber, this));
        RCLCPP_INFO(this->get_logger(), "Number publisher has been started.");
    }

private:
    void publishNumber()
    {
        auto msg = example_interfaces::msg::Int64();
        msg.data = number_;
        number_publisher_->publish(msg);
    }

    int number_;
    rclcpp::Publisher<example_interfaces::msg::Int64>::SharedPtr number_publisher_;
    rclcpp::TimerBase::SharedPtr number_timer_;
};

int main(int argc, char **argv)
{
    rclcpp::init(argc, argv);
    auto node = std::make_shared<NumberPublisherNode>();
    rclcpp::spin(node);
    rclcpp::shutdown();
    return 0;
}

number_publisher.py

      

      

      

    
    

      <python />
    
#!/usr/bin/env python3
import rclpy
from rclpy.node import Node

from example_interfaces.msg import Int64

class NumberPublisherNode(Node):
    def __init__(self):
        super().__init__("number_publisher")
				# add this lines
        self.declare_parameter("test1")
        self.declare_parameter("test2")
				# -------------------

        self.number_ = 2
        self.number_publisher_ = self.create_publisher(Int64, "number", 10)
        self.number_timer_ = self.create_timer(1.0, self.publish_number)
        self.get_logger().info("Number publisher has been started.")

    def publish_number(self):
        msg = Int64()
        msg.data = self.number_
        self.number_publisher_.publish(msg)

def main(args=None):
    rclpy.init(args=args)
    node = NumberPublisherNode()
    rclpy.spin(node)
    rclpy.shutdown()

if __name__ == "__main__":
    main()

      

      

      

    
    

      <bash />
    
ros2 run my_py_pkg number_publisher
ros2 run my_py_pkg number_counter

ros2 param list
"
/number_publisher:
  test1
	test2
  use_sim_time
/number_counter:
	use_sim_time
"

ros2 param get /number_publisher use_sim_time
# Boolean value is: False

Whenever you start a node, you automatically have this parameter use_sim_time by ros2

But you don’t care about this parameter. It just will allow you to easily find what are parameters currently running on application. And those are different parameters even if they have same names.

Let’s set parameters!

      

      

      

    
    

      <bash />
    
ros2 run my_py_pkg number_publisher --ros-args -p test1:=3
ros2 run my_py_pkg number_publisher --ros-args -p test2:="hello"

ros2 param get /number_publisher test1
# Integer value is: 3
ros2 param get /number_publisher test2
# String value is: hello

3. Get Parameters

      

      

      

    
    

      <python />
    
#!/usr/bin/env python3
import rclpy
from rclpy.node import Node

from example_interfaces.msg import Int64

class NumberPublisherNode(Node):
    def __init__(self):
        super().__init__("number_publisher")
        self.declare_parameter("number_to_publish", 2) # second parameter is default value
        self.declare_parameter("publish_frequency", 1.0)

        self.number_ = self.get_parameter("number_to_publish").value
        self.publisher_frequeny_ = self.get_parameter("publish_frequency").value

        self.number_publisher_ = self.create_publisher(Int64, "number", 10)
        self.number_timer_ = self.create_timer(
            1.0 / self.publisher_frequeny_, self.publish_number)
        self.get_logger().info("Number publisher has been started.")

    def publish_number(self):
        msg = Int64()
        msg.data = self.number_
        self.number_publisher_.publish(msg)

def main(args=None):
    rclpy.init(args=args)
    node = NumberPublisherNode()
    rclpy.spin(node)
    rclpy.shutdown()

if __name__ == "__main__":
    main()

      

      

      

    
    

      <bash />
    
ros2 run my_py_pkg number_publisher --ros-args -p number_to_publish:=3 -p publish_frequency:=4

ros2 topic echo /number 
"
data: 2
---
data: 2
---
"

ros2 topic hz /number 
"
average rate: 4.000
	min: 0.235s max: 0.261s std dev: 0.00800s window: 6
average rate: 4.000
	min: 0.235s max: 0.261s std dev: 0.00597s window: 11
average rate: 4.000
	min: 0.235s max: 0.261s std dev: 0.00534s window: 16
"

4. Activity

Let’s practice a little bit more with Parameters.

Here are 2 quick activities:

 

1. Do you remember one of the first node we created in the Topic section, with the robot news radio? This node publishes a string on a topic, similar to this “Hi, this is R2D2 from the Robot News Station!”.

Now, it would be better if we could set the robot’s name at run time, so we can launch the node multiple times with different robot names.

Add a “robot_name” parameter, and use the value to publish the string on the “robot_news” topic. Your string template (“Hi, this is <robot_name> from the Robot News Station!”) will now use the name you set at runtime.

 

2. Go back to the “led_panel_node”. Here you have an int array representing the states of your LEDs (0 for powered off, 1 for powered on). Set this array with a parameter named “led_states”.

---

This will make you practice on string, integer, and array parameters. You can apply those changes in both the Python and Cpp nodes.

5. Solution

robot_news_station.py

      

      

      

    
    

      <python />
    
#!/usr/bin/env python3
import rclpy
from rclpy.node import Node

from example_interfaces.msg import String

class RobotNewsStationNode(Node):
    def __init__(self):
        super().__init__("robot_news_station")
        self.declare_parameter("robot_name", "C3PO")

        self.robot_name_ = self.get_parameter("robot_name").value
        self.publisher_ = self.create_publisher(String, "robot_news", 10)
        self.timer_ = self.create_timer(0.5, self.publish_news)
        self.get_logger().info("Robot News Station has been started")

    def publish_news(self):
        msg = String()
        msg.data = "Hi, this is " + \\
            str(self.robot_name_) + " from the robot news station."
        self.publisher_.publish(msg)

def main(args=None):
    rclpy.init(args=args)
    node = RobotNewsStationNode()
    rclpy.spin(node)
    rclpy.shutdown()

if __name__ == "__main__":
    main()

led_panel.py

      

      

      

    
    

      <python />
    
#!/usr/bin/env python3
import rclpy
from rclpy.node import Node

from my_robot_interfaces.msg import LedStateArray
from my_robot_interfaces.srv import SetLed

class LedPanelNode(Node):
    def __init__(self):
        super().__init__("led_panel")
        self.declare_parameter("led_states", [0, 0, 0])

        self.led_states_ = self.get_parameter("led_states").value
        self.led_states_publisher_ = self.create_publisher(
            LedStateArray, "led_states", 10)
        self.led_states_timer_ = self.create_timer(4, self.publish_led_states)
        self.set_led_service_ = self.create_service(
            SetLed, "set_led", self.callback_set_led)
        self.get_logger().info("LED panel node has been started.")

    def publish_led_states(self):
        msg = LedStateArray()
        msg.led_states = self.led_states_
        self.led_states_publisher_.publish(msg)

    def callback_set_led(self, request, response):
        led_number = request.led_number
        state = request.state

        if led_number > len(self.led_states_) or led_number <= 0:
            response.success = False
            return response

        if state not in [0, 1]:
            response.success = False
            return response

        self.led_states_[led_number - 1] = state
        response.success = True
        self.publish_led_states()
        return response

def main(args=None):
    rclpy.init(args=args)
    node = LedPanelNode()
    rclpy.spin(node)
    rclpy.shutdown()

if __name__ == "__main__":
    main()

robot_news_station.cpp

      

      

      

    
    

      <cpp />
    
#include "rclcpp/rclcpp.hpp"
#include "example_interfaces/msg/string.hpp"

class RobotNewsStationNode : public rclcpp::Node
{
public:
    RobotNewsStationNode() : Node("robot_news_station"), robot_name_("R2D2")
    {
        this->declare_parameter("robot_name", "R2D2");
        robot_name_ = this->get_parameter("robot_name").as_string();

        publisher_ = this->create_publisher<example_interfaces::msg::String>("robot_news", 10);
        timer_ = this->create_wall_timer(std::chrono::milliseconds(500),
                                         std::bind(&RobotNewsStationNode::publishNews, this));
        RCLCPP_INFO(this->get_logger(), "Robot News Station has been started.");
    }

private:
    void publishNews()
    {
        auto msg = example_interfaces::msg::String();
        msg.data = std::string("Hi, this is ") + robot_name_ + std::string(" from the Robot News Station");
        publisher_->publish(msg);
    }

    std::string robot_name_;
    rclcpp::Publisher<example_interfaces::msg::String>::SharedPtr publisher_;
    rclcpp::TimerBase::SharedPtr timer_;
};

int main(int argc, char **argv)
{
    rclcpp::init(argc, argv);
    auto node = std::make_shared<RobotNewsStationNode>();
    rclcpp::spin(node);
    rclcpp::shutdown();
    return 0;
}

led_panel.cpp

      

      

      

    
    

      <cpp />
    
#include "rclcpp/rclcpp.hpp"
#include "my_robot_interfaces/msg/led_state_array.hpp"
#include "my_robot_interfaces/srv/set_led.hpp"

class LedPanelNode : public rclcpp::Node
{
public:
    LedPanelNode() : Node("led_panel")
    {
        this->declare_parameter("led_states", std::vector<int64_t>{0, 0, 0});
        led_states_ = this->get_parameter("led_states").as_integer_array();

        led_states_publisher_ =
            this->create_publisher<my_robot_interfaces::msg::LedStateArray>("led_states", 10);
        led_states_timer_ =
            this->create_wall_timer(std::chrono::seconds(4),
                                    std::bind(&LedPanelNode::publishLedStates, this));
        set_led_service_ = this->create_service<my_robot_interfaces::srv::SetLed>(
            "set_led",
            std::bind(&LedPanelNode::callbackSetLed, this, std::placeholders::_1, std::placeholders::_2));
        RCLCPP_INFO(this->get_logger(), "Led panel node has been started");
    }

private:
    void publishLedStates()
    {
        auto msg = my_robot_interfaces::msg::LedStateArray();
        msg.led_states = led_states_;
        led_states_publisher_->publish(msg);
    }

    void callbackSetLed(const my_robot_interfaces::srv::SetLed::Request::SharedPtr request,
                        const my_robot_interfaces::srv::SetLed::Response::SharedPtr response)
    {
        int64_t led_number = request->led_number;
        int64_t state = request->state;

        if (led_number > (int64_t)led_states_.size() || led_number <= 0)
        {
            response->success = false;
            return;
        }

        if (state != 0 && state != 1)
        {
            response->success = false;
            return;
        }

        led_states_.at(led_number - 1) = state;
        response->success = true;
        publishLedStates();
    }

    std::vector<int64_t> led_states_;

    rclcpp::Publisher<my_robot_interfaces::msg::LedStateArray>::SharedPtr led_states_publisher_;
    rclcpp::TimerBase::SharedPtr led_states_timer_;
    rclcpp::Service<my_robot_interfaces::srv::SetLed>::SharedPtr set_led_service_;
};

int main(int argc, char **argv)
{
    rclcpp::init(argc, argv);
    auto node = std::make_shared<LedPanelNode>();
    rclcpp::spin(node);
    rclcpp::shutdown();
    return 0;
}