ROS2—— Use of parameters

Last time when it comes to , Organization Give everyone free 2 A hamburger , one day Organization In business , Hamburgers are suddenly in short supply , The leader decided to change the rules temporarily , After that, everyone can only get one hamburger . But the node is already running , How to change this value ? This requires parameters parameters

Parameter Introduction

Parameter is the configuration parameter value of the node . You can think of parameters as part of node configuration . The parameter is an integer , Floating point numbers , Boolean value , Strings and lists . stay ROS2 in , Each node has its own parameters . All parameters are dynamically reconfigurable , And based on ROS2 Service built .

In this case , The number of hamburgers per person can be Organization A parameter of the node .

below , We will modify this service program , Change the number of hamburgers per capita by modifying the parameters

Modify the service program

newly build Organization_with_parameter.cpp file

Code from Organization.cpp To modify , Use... In different places // CHANGE: Marked out , Please compare yourself with the code in the previous section .

#include "rclcpp/rclcpp.hpp"
#include "service_interfaces/srv/calculate.hpp"

using std::placeholders::_1;
using std::placeholders::_2;

class Organization : public rclcpp::Node 
{
    

public:
    Organization() : Node("Organization"), NumOfAll(100)
    {
    
        RCLCPP_INFO(this->get_logger(), " Hello everyone ,  We are an enthusiastic organization ,  We only give poorer Hair hamburger .");
        callback_group_organization = this->create_callback_group(rclcpp::CallbackGroupType::MutuallyExclusive);
        Organization_Server = this->create_service<service_interfaces::srv::Calculate>("Calculate",
                                    std::bind(&Organization::organization_callback,this,_1,_2),
                                    rmw_qos_profile_services_default,
                                    callback_group_organization);
        
        // CHANGE:  Declare parameters 
        this->declare_parameter<int>("NumOfEachPerson", NumOfEachPerson);
    }

private:
    size_t NumOfAll;

    // CHANGE:  State how many hamburgers each person gets ,  The default is 2
    int NumOfEachPerson = 2;

    rclcpp::CallbackGroup::SharedPtr callback_group_organization;
    rclcpp::Service<service_interfaces::srv::Calculate>::SharedPtr Organization_Server;

    void organization_callback(const service_interfaces::srv::Calculate::Request::SharedPtr request,
                               const service_interfaces::srv::Calculate::Response::SharedPtr response)
    {
    
        if(request->status == "Poorer")
        {
    
            RCLCPP_INFO(this->get_logger(), " Received a message from %s Request , He has %d personal .", request->status.c_str(), request->num_of_people);
            
            // CHANGE:  Update parameters 
            this->get_parameter("NumOfEachPerson", NumOfEachPerson);
            
            // CHANGE:  Calculate the number of hamburgers to be given , Given by parameters 
            unsigned int NumOfRequired = request->num_of_people * NumOfEachPerson;

            if(NumOfRequired > NumOfAll)
            {
    
                RCLCPP_INFO(this->get_logger(), " At present, there are only %d A hamburger !  Not enough points ,  Please come back tomorrow .", NumOfRequired);
                response->success = false;
            }
            else
            {
    
                NumOfAll -= NumOfRequired;
                response->num_of_hamburger = NumOfRequired;
                response->success = true;
                RCLCPP_INFO(this->get_logger(), " Successfully send out %d A hamburger ~  Remnant %d A hamburger ", NumOfRequired, NumOfAll);
            }
        }
        else
        {
    
            response->success = false;
            response->num_of_hamburger = 0;
            RCLCPP_INFO(this->get_logger(), " Received an illegal request , This man is %s,  Not qualified to send hamburgers .", request->status.c_str());
        }
    }
};

int main(int argc, char **argv)
{
    
    rclcpp::init(argc, argv);
    auto node = std::make_shared<Organization>();
    rclcpp::executors::MultiThreadedExecutor exector;
    exector.add_node(node);
    exector.spin();
    rclcpp::shutdown();
    return 0;
}

Cmakelist.txt

add to :

add_executable(Organization_with_parameters_node src/Organization_with_parameters.cpp)
ament_target_dependencies(Organization_with_parameters_node rclcpp service_interfaces)

add to :Organization_with_parameters_node

install(TARGETS
  ...
  Organization_with_parameters_node
  DESTINATION lib/${PROJECT_NAME}
)

package.xml

No need to modify

compile

--packages-select Specify compile customer_and_kfc Function pack

colcon build --packages-select poor_and_organization

Refresh the environment

source ~/.bashrc

function

Create a new terminal window , Run... With parameters Organization Server node

ros2 run poor_and_organization Organization_with_parameters_node

Create another terminal , function Poor Client node

At first, each person received two hamburgers , Run the client directly :

ros2 run poor_and_organization Poor_node Poorer 5

Organization Server side : Successfully issued 10 A hamburger

Poor client : Successfully received 10 A hamburger

At this point, you need to modify the parameters , Another terminal , function :

ros2 param set /Organization NumOfEachPerson 1

The following prompt is success

Run the client again

ros2 run poor_and_organization Poor_node Poorer 50

Poor client : 50 I received 50 A hamburger

Organization Server side : Successfully issued 50 A hamburger

thus it can be seen , The parameters were successfully modified , But the parameters at this time will not be retained , After the node where the parameter is located is restarted, it will be restored to the initial value . If a node has many parameters , After modification, how should I save the current parameters for the next call ? Please read on .

Parameters common commands

Use ros2 param

Check the parameter list

ros2 param list

It can also be specific to a node

ros2 param list /Organization

View parameter description

ros2 param describe /Organization NumOfEachPerson

Get parameter value

ros2 param get <node_name> <parameter_name>

ros2 param get /Organization NumOfEachPerson

Set the parameter value

ros2 param set <node_name> <parameter_name> <value>

ros2 param set /Organization NumOfEachPerson 1

Get the parameter value again , It has changed :

Save parameters

ros2 param dump <node_name>

ros2 param dump /Organization

In the root directory of the current terminal , You can see that an Organization.yaml file , Open this file

/Organization:
  ros__parameters:
    NumOfEachPerson: 1
    use_sim_time: false

With this parameter file , You can set the parameters of the node through this file

Load parameters

Load parameters after the node is started

ros2 param load <node_name> <parameter_file>

ros2 param load /Organization ./Organization.yaml

The following information is returned to indicate successful loading :

Load parameters before node startup

ros2 run <package_name> <executable_name> --ros-args --params-file <file_name>

ros2 run poor_and_organization Organization_with_parameters_node --ros-args --params-file ./Organization.yaml 

Please try to get the current NumOfEachPerson Value as an exercise .

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