ROS Learning Notes

ROS Learning Notes 08

Keypoints

• Parameter server
• rosparam command
• Example

Parameter server

• Parameter server is a dictionary that stores parameters, i.e. stores global variable.
• Different nodes in different PCs can access the parameter server to get parameters.

rosparam command

• rosparam command is used to get and set parameters in the parameter server.
  • rosparam list : list all parameters in the parameter server
  • rosparam get /parameter_name : get the value of the parameter
  • rosparam set /parameter_name value : set the value of the parameter
  • rosparam dump file_name : dump all parameters in the parameter server to a file in current directory
  • rosparam load file_name : load parameters from a file to the parameter server
  • rosparam delete /parameter_name : delete the parameter

Example

• CPP

    #include <ros/ros.h>
    #include <std_srvs/Empty.h>
  
    int main(int argc, char **argv)
    {
        int red, green, blue;
        ros::init(argc, argv, "parameter_config");
        ros::NodeHandle nh;
  
        ros::param::get("/turtlesim/background_r", red);
        ros::param::get("/turtlesim/background_g", green);
        ros::param::get("/turtlesim/background_b", blue);
  
        ROS_INFO("Get background color: R-%d, G-%d, B-%d", red, green, blue);
  
        ros::param::set("/turtlesim/background_r", 255);
        ros::param::set("/turtlesim/background_g", 255);
        ros::param::set("/turtlesim/background_b", 255);
  
        ROS_INFO("Set Background Color to [255, 255, 255]");
  
        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 background color: R-%d, G-%d, B-%d", red, green, blue);
  
        // below section equals to `rosservice call /clear "{}"` in terminal
        ros::service::waitForService("/clear");
        ros::ServiceClient clear_background_ = nh.serviceClient<std_srvs::Empty>("/clear");
        std_srvs::Empty srv;
        clear_background_.call(srv);
  
        sleep(1);
  
        return 0;
    }
  

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

    catkin_make
    source devel/setup.bash
    roscore
    rosrun turtlesim turtlesim_node
    rosrun learning_parameter parameter_config
  

  When set rosparam in terminal like /turtlesim/background_r 255, rosservice call /clear "{}" is needed to refresh the background color.

• Python

    #!/usr/bin/env python
    # -*- coding: utf-8 -*-
  
    import rospy
    import sys
    from std_srvs.srv import Empty
  
    def parameter_config():
      rospy.init_node('parameter_config', anonymous=True)
  
      red = rospy.get_param('/turtlesim/background_r')
      green = rospy.get_param('/turtlesim/background_g')
      blue = rospy.get_param('/turtlesim/background_b')
  
      rospy.loginfo("Get background color: R-%d, G-%d, B-%d", red, green, blue)
  
      rospy.set_param('/turtlesim/background_r', 255)
      rospy.set_param('/turtlesim/background_g', 255)
      rospy.set_param('/turtlesim/background_b', 255)
  
      rospy.loginfo("Set Background Color to [255, 255, 255]")
  
      red = rospy.get_param('/turtlesim/background_r')
      green = rospy.get_param('/turtlesim/background_g')
      blue = rospy.get_param('/turtlesim/background_b')
  
      rospy.loginfo("Re-get background color: R-%d, G-%d, B-%d", red, green, blue)
  
      rospy.wait_for_service('/clear')
      try:
          clear_background_ = rospy.ServiceProxy('/clear', Empty)
          clear_background_()
      except rospy.ServiceException as e:
          print("Service call failed: %s"%e)
  
      if __name__ == '__main__':
          parameter_config()
  

---