[ROS Study Notes] (IX) Using ROS Parameters from the Command Line and in Code

I. Parameter Model

ROS Master includes a Parameter Server, which is a global dictionary that stores configuration parameters. These configuration parameters are globally accessible to all nodes.

II. Usage

1. List All Current Parameters

rosparam list

2. Display a Parameter Value

rosparam get param_key

3. Set a Parameter Value

rosparam set param_key param_value

4. Save Parameters to a File

rosparam dump file_name

5. Read Parameters from a File

rosparam load file_name

6. Delete a Parameter

rosparam delete param_key

III. Example

1. Create a Package

cd ~/catkin_ws/src
catkin_create_pkg learning_parameter roscpp rospy std_srvs

2. Open the Turtlesim Simulator

Open a terminal and start roscore:

roscore

Open another terminal and run the turtlesim simulation:

rosrun turtlesim turtlesim_node

3. Using rosparam from the Command Line

(1) View the parameter list

rosparam list

(2) Get the values: RGB values of the background color

rosparam get /turtlesim/background_r
rosparam get /turtlesim/background_g
rosparam get /turtlesim/background_b

(3) Modify a value: change the background color

rosparam set /turtlesim/background_b 100

Send the request again to refresh the background color:

rosservice call /clear "{}"

(4) Save parameters to a file

rosparam dump param.yaml

By default, the parameters are saved in the current directory.

(5) Load a parameter file

Open the parameter file you just saved and modify its parameter values.

rosparam load param.yaml

This updates the system parameters with the parameter values in the file.

(6) Delete a parameter

rosparam delete /turtlesim/background_g

View the parameter list:

rosparam list

Refresh the turtlesim simulator’s background color:

rosservice call /clear "{}"

IV. Getting and Setting Parameter Values Programmatically

1. Write the C++ Program

Create a file named parameter_config.cpp in the learning_parameter/src/ directory.

Its contents are:

/**
 * 该例程设置/读取海龟例程中的参数
 * REFERENCE：www.guyuehome.com
 */
#include <string>
#include <ros/ros.h>
#include <std_srvs/Empty.h>

int main(int argc, char **argv)
{
	int red, green, blue;

    // ROS节点初始化
    ros::init(argc, argv, "parameter_config");

    // 创建节点句柄
    ros::NodeHandle node;

    // 读取背景颜色参数
	ros::param::get("/turtlesim/background_r", red);
	ros::param::get("/turtlesim/background_g", green);
	ros::param::get("/turtlesim/background_b", blue);

	ROS_INFO("Get Backgroud Color[%d, %d, %d]", red, green, blue);

	// 设置背景颜色参数
	ros::param::set("/turtlesim/background_r", 255);
	ros::param::set("/turtlesim/background_g", 255);
	ros::param::set("/turtlesim/background_b", 255);

	ROS_INFO("Set Backgroud Color[255, 255, 255]");

    // 读取背景颜色参数
	ros::param::get("/turtlesim/background_r", red);
	ros::param::get("/turtlesim/background_g", green);
	ros::param::get("/turtlesim/background_b", blue);

	ROS_INFO("Re-get Backgroud Color[%d, %d, %d]", red, green, blue);

	// 调用服务，刷新背景颜色
	ros::service::waitForService("/clear");
	ros::ServiceClient clear_background = node.serviceClient<std_srvs::Empty>("/clear");
	std_srvs::Empty srv;
	clear_background.call(srv);
	
	sleep(1);

    return 0;
}

2. Compile the Program

In learning_parameter/, open CMakeList.txt and add the following build rules above install.

add_executable(parameter_config src/parameter_config.cpp)
target_link_libraries(parameter_config ${catkin_LIBRARIES})

Compile the program:

cd catkin_ws
catkin_make

3. Run the Program

Run roscore:

roscore

Run the turtlesim simulation:

rosrun turtlesim turtlesim_node

Run the node you just wrote:

rosrun learning_parameter parameter_config

You will see that the turtle’s color has changed, indicating that the program ran successfully.