【嵌入式应用2】创建工作空间和功能包，使用launch文件启动结点，完成海龟旋转

题目

创建一个工作空间和功能包，然后在功能包中完成如下工作，并且使用launch文件启动涉及的节点;话题与服务编程:通过代码新生一只海龟，放置在(5, 5)点，命名为“turtle2” ;通过代码订阅turtle2的实时位置并在终端打印;控制turtle2实现旋转运动;

1.进入工作区间

cd catkin_ws/src/

2.新建一个工程包

catkin_create_pkg lesson2_homework std_msgs rospy roscpp

3.进入包内的src文件夹新建一个cpp

cd lesson2_homework/src/
vi turtle_control.cpp

粘贴以下代码：

#include 
#include 
#include 
#include 
ros::Publisher turtle_vel;
void poseCallback(const turtlesim::PoseConstPtr& msg)
{
    ROS_INFO("Turtle2 position:(%f %f)",msg->x,msg->y);
}
int main(int argc,char** argv)
{
    //初始化节点
    ros::init(argc,argv,"turtle_control");
    ros::NodeHandle node;
    //通过服务调用，产生第二只乌龟turtle2
    ros::service::waitForService("spawn");
    ros::ServiceClient add_turtle=node.serviceClient<turtlesim::Spawn>("spawn");
    turtlesim::Spawn srv;
    srv.request.x=5;
    srv.request.y=5;
    srv.request.name="turtle2";
    add_turtle.call(srv);
    ROS_INFO("The turtle2 has been spawn!");
    //订阅乌龟的pose信息
    ros::Subscriber sub=node.subscribe("turtle2/pose",10,&poseCallback);
    //定义turtle的速度控制发布器
    turtle_vel=node.advertise<geometry_msgs::Twist>("turtle2/cmd_vel",10);
    ros::Rate rate(10.0);
    while(node.ok())
    {
       //发布速度控制命令
        geometry_msgs::Twist vel_msg;
        vel_msg.angular.z=1;
        vel_msg.linear.x=1;
        turtle_vel.publish(vel_msg);
        ros::spinOnce();
        rate.sleep();
    }
    return 0;
}

4.回到上层目录，修改Cmakelist.txt

cd ../
gedit Cmakelist.txt

文本最末未添加：

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

5.新建launch文件夹，进入文件夹，新建turtle_control.launch

mkdir launch
cd launch/
vi turtle_control.launch

添加以下代码：

<launch>
<node pkg="turtlesim" type="turtlesim_node" name="turtlesim_node"/>
<node pkg="lesson2_homework" type="turtle_control" name="turtle_control" output="screen"/>
</launch>

6.回到工作区间，编译

cd ~/catkin_ws
catkin_make

7.新建终端，启动ros核心程序

roscore

8.注册程序

cd catkin_ws/
source ./devel/setup.bash

9.运行程序

rosrun lesson2_homework turtle_control 

10.新建终端，启动结点

rosrun turtlesim turtlesim_node

11.出现一个小海龟不停的转圈，并且在之前运行程序的终端上会

不停的打印小海龟的位置

参考链接:https://blog.csdn.net/sanyiji/article/details/104715216/