ROS notes (09) - query and setting of parameters

Parameter server in ROS It is mainly used to realize data sharing between different nodes . The parameter server is then equivalent to a common container independent of all nodes , You can store data in this container , Called by different nodes , Of course, different nodes can also store data , The typical application scenarios of the parameter server are as follows :

When navigation is implemented , We'll do path planning , such as : Global path planning , Design an approximate path from the starting point to the target point . Local path planning , The travel path will be generated according to the current road conditions

In the above scenario , Global path planning and local path planning , The parameter server will be used ：

Path planning , It is necessary to refer to the size of the trolley , We can store these size information in the parameter server , Global path planning nodes and local path planning nodes can middle note these parameters from the parameter server.

Parameter server , It is generally applicable to some application scenarios with data sharing .

1. Parametric model

As shown above , The parametric model can be seen as ROS The global dictionary of , Each node Node The corresponding parameter information can be obtained from the parameter model .

For details, please refer to ：http://wiki.ros.org/Parameter%20server

2. Common parameter command line

Common parameter command lines are as follows

$ rosparam
rosparam is a command-line tool for getting, setting, and deleting parameters from the ROS Parameter Server.

Commands:
	rosparam set	set parameter
	rosparam get	get parameter
	rosparam load	load parameters from file
	rosparam dump	dump parameters to file
	rosparam delete	delete parameter
	rosparam list	list parameter names

• List all current parameters

$ rosparam list
/rosdistro
/roslaunch/uris/host_wohu_pc__42765
/rosversion
/run_id
/turtlesim/background_b
/turtlesim/background_g
/turtlesim/background_r

• Display a parameter value

$ rosparam get /run_id 
b37e6c1a-f0fe-11ec-92ca-00e070ce7d11
$ rosparam get /turtlesim/background_b
255

• Set a parameter value

$ rosparam set /turtlesim/background_b 100
$ rosparam get /turtlesim/background_b
100
$ rosservice call /clear "{}"  #  Used to make the new value of the setting effective 

• Save parameters to file

$ rosparam dump config
$ ls
build  config  devel  src
$ cat config 
rosdistro: 'melodic '
roslaunch:
  uris: {
    host_wohu_pc__42765: 'http://wohu-pc:42765/'}
rosversion: '1.14.13 '
run_id: b37e6c1a-f0fe-11ec-92ca-00e070ce7d11
turtlesim: {
    background_b: 100, background_g: 86, background_r: 69}

• Read parameters from file

$ rosparam load  config 
$ rosservice call /clear "{}"

• Delete parameters

$ rosparam set /aaa 100
$ rosparam get /aaa
100
$ rosparam delete /aaa 

3. Parameter storage format

All parameters are stored in one YAML Format file .

rosdistro: 'melodic

  '
roslaunch:
  uris: {
    host_wohu_pc__42765: 'http://wohu-pc:42765/'}
rosversion: '1.14.13

  '
run_id: b37e6c1a-f0fe-11ec-92ca-00e070ce7d11
turtlesim: {
    background_b: 100, background_g: 86, background_r: 69}

4. Parameter setting and query code

#!/usr/bin/env python
# -*- coding: utf-8 -*-

#  This routine sets / Read the parameters in the turtle routine 

import sys
import rospy
from std_srvs.srv import Empty

def parameter_config():
	# ROS Node initialization 
    rospy.init_node('parameter_config', anonymous=True)

	#  Read background color parameters 
    red   = rospy.get_param('/turtlesim/background_r')
    green = rospy.get_param('/turtlesim/background_g')
    blue  = rospy.get_param('/turtlesim/background_b')

    rospy.loginfo("Get Backgroud Color[%d, %d, %d]", red, green, blue)

	#  Set the background color parameters 
    rospy.set_param("/turtlesim/background_r", 255);
    rospy.set_param("/turtlesim/background_g", 255);
    rospy.set_param("/turtlesim/background_b", 255);

    rospy.loginfo("Set Backgroud Color[255, 255, 255]");

	#  Read background color parameters 
    red   = rospy.get_param('/turtlesim/background_r')
    green = rospy.get_param('/turtlesim/background_g')
    blue  = rospy.get_param('/turtlesim/background_b')

    rospy.loginfo("Get Backgroud Color[%d, %d, %d]", red, green, blue)

	#  Find out /spawn After service , Create a service client , The connection name is /spawn Of service
    rospy.wait_for_service('/clear')
    try:
        clear_background = rospy.ServiceProxy('/clear', Empty)

		#  Request service call , Enter request data 
        response = clear_background()
        return response
    except rospy.ServiceException, e:
        print "Service call failed: %s"%e

if __name__ == "__main__":
    parameter_config()

function

$ cd ~/catkin_ws
$ catkin_create_pkg  parameter  rospy std_msgs geometry_msgs turtlesim
$ catkin_make
$ source ./devel/setup.bash

take Python Put the code in the following path

Carry on

$ roscore
$ rosrun turtlesim turtlesim_node
$ rosrun parameter parameter_config.py

The results change