ROS中Service编程实现

文章目录

• 简介
• C++
• • 1.代码
  • 2.在CMakeLists中添加编译依赖
  • 3.编译
  • 4.修改环境变量
  • 5.执行
  • 6.调用服务
  • 7.结果
• python
• 总结

简介

实现一个代码，创建一个服务，控制小海龟的运动

C++

1.代码

#include <ros/ros.h>
#include <geometry_msgs/Twist.h>
#include <std_srvs/Trigger.h> //服务数据类型是std_srvs/Trigger
ros::Publisher turtle_vel_pub;
bool pubCommand = false;
bool commandCallback(std_srvs::Trigger::Request &req, std_srvs::Trigger::Response &res)
{
	pubCommand = !pubCommand;
	//显示请求数据
	ROS_INFO("Publish turtle velocity command [%s]",pubCommand == true ? "Yes" : "No");
	//设置反馈数据
	res.success = true;
	res.message = "Change turtle command state";
	return true;
}
int main(int argc, char **argv)
{
	//初始化节点
	ros::init(argc, argv, "turtle_command_server");
	//创建节点句柄
	ros::NodeHandle n;
	//创建一个名为/turtle_command的server，注册回调函数commandCallback
	ros::ServiceServer command_service = n.advertiseService("/turtle_command", commandCallback);
	//创建一个Publisher, 发布名为/turtle/cmd_vel的topic,消息类型为geometry_msgs::Twsit,队列长度为10
	turtle_vel_pub = n.advertise<geometry_msgs::Twist>("/turtle1/cmd_vel", 10);
	//循环等待回调函数
	ROS_INFO("Ready to receive turtle command");
	//设置循环频率
	ros::Rate loop_rate(10);
	while(ros::ok())
	{
		//查看一次回调函数列表
		ros::spinOnce();
		//如果标志为true，则发布速度质量
		if(pubCommand)
		{
			geometry_msgs::Twist vel_msg;
			vel_msg.linear.x = 2.0;
			vel_msg.angular.z = 2.0;
			turtle_vel_pub.publish(vel_msg);
		}
		//按照循环频率延时
		loop_rate.sleep();
	}
	
}

注意
回调函数会传入两个参数一个是request，一个是responce

2.在CMakeLists中添加编译依赖

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

注意
catkin_LIBRARIES是前小写后大写

3.编译

回到工作目录
catkin_make

4.修改环境变量

source src/setup.bash

5.执行

rosrun learning_service turtle_command_server
执行后就会产生一个turtle_command的服务

6.调用服务

rosservice call /turtle_command "{}"

7.结果

1. 调用服务
   
2. 执行服务操作后产生反馈
   
3. 结果小海龟画圆
   

python

#!/usr/bin/env python3 
#-*- coding:utf-8 -*-
#该程序将执行/turtle_command服务,服务数据类型std_srvs/Trigger
import rospy
import _thread, time
from geometry_msgs.msg import Twist
from std_srvs.srv import Trigger, TriggerResponse

pubCommand = False
turtle_vel_pub = rospy.Publisher('/turtle1/cmd_vel', Twist, queue_size = 10)
def command_thread():
	while True:
		if pubCommand:
			vel_msg = Twist()
			vel_msg.linear.x = 0.5
			vel_msg.angular.z = 0.2
			turtle_vel_pub.publish(vel_msg)
			
		time.sleep(0.1)
def commandCallback(req):
	global pubCommand
	pubCommand = bool(1 - pubCommand)
	
	#显示请求数据
	rospy.loginfo("Publish turtle velocity command![%d]",pubCommand)
	#反馈数据
	return TriggerResponse(1, "Change turtle command state!")
def turtle_command_server():
	#初始化节点
	rospy.init_node('turtle_command_server')
	#创建一个名为/turtle_command的server, 注册回调函数commandCallback
	s = rospy.Service('/turtle_command', Trigger, commandCallback)
	#循环等待回调函数
	print("Ready to receive turtlre command")
	_thread.start_new_thread(command_thread, ())
	rospy.spin()
if __name__ == '__main__':
	turtle_command_server()

运行的步骤和前几篇文章是一样的。
运行代码后会出现名为turtle_command的service。这是自己定义的

总结

实现服务器的步骤大概是

1. 初始化节点
2. 创建Server实例
3. 循环等待服务请求，进入回调函数
4. 在回调函数中完成服务功能的处理，并反馈应答数据