ROS学习记录：创建一个工作空间和功能包，完成话题与服务编程

一、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，并使用launch文件启动涉及的节点

1、创建工作空间然后编译工作区

创建工作空间：

mkdir -p ~/catkin_ws/src

进入src目录编译工作区：

catkin_init_workspace

在catkin_ws目录下注册工作区：

source devel/setup.bash  
echo $ROS_PACKAGE_PATH 

2、创建工程包、编译

在catkin_ws/src下创建名称为beginner_tutorials的功能包：

catkin_create_pkg beginner_tutorials std_msgs rospy roscpp

回到catkin_ws目录下执行如下命令编译：

catkin_make

如下图所示，编译成功

3、写一个发布节点，在创建的工程包的src目录下创建talker.cpp和listener.cpp

talker.cpp

#include "ros/ros.h"
#include "std_msgs/String.h"
 
#include 
int main(int argc, char **argv)
{
  ros::init(argc, argv, "talker");
  ros::NodeHandle n;
  ros::Publisher chatter_pub = n.advertise<std_msgs::String>("chatter", 1000);
  ros::Rate loop_rate(10);
  /**
   * A count of how many messages we have sent. This is used to create
   * a unique string for each message.
   */
  int count = 0;
  while (ros::ok())
  {
    /**
     * This is a message object. You stuff it with data, and then publish it.
     */
    std_msgs::String msg;
 
    std::stringstream ss;
    ss << "hello world " << count;
    msg.data = ss.str();
 
    ROS_INFO("%s", msg.data.c_str());
 
    chatter_pub.publish(msg);
 
    ros::spinOnce();
 
    loop_rate.sleep();
    ++count;
  }
  return 0;
}

listener.cpp

#include "ros/ros.h"
#include "std_msgs/String.h"
 
/**
 * This tutorial demonstrates simple receipt of messages over the ROS system.
 */
void chatterCallback(const std_msgs::String::ConstPtr& msg)
{
  ROS_INFO("I heard: [%s]", msg->data.c_str());
}
 
int main(int argc, char **argv)
{
  ros::init(argc, argv, "listener");
  ros::NodeHandle n;
  ros::Subscriber sub = n.subscribe("chatter", 1000, chatterCallback);
  /**
   * ros::spin() will enter a loop, pumping callbacks.  With this version, all
   * callbacks will be called from within this thread (the main one).  ros::spin()
   * will exit when Ctrl-C is pressed, or the node is shutdown by the master.
   */
  ros::spin();
  return 0;
}

然后在创建的功能包下的Cmakelist.txt文件里添加依赖项：

在Cmakelist.txt文件末尾加上如下代码：

include_directories(include ${catkin_INCLUDE_DIRS})

add_executable(talker src/talker.cpp)
target_link_libraries(talker ${catkin_LIBRARIES})
add_dependencies(talker beginner_tutorials_generate_messages_cpp)

add_executable(listener src/listener.cpp)
target_link_libraries(listener ${catkin_LIBRARIES})
add_dependencies(listener beginner_tutorials_generate_messages_cpp)

切换到工作空间，执行编译命令：

cd ~/catkin_ws
catkin_make

出现如下画面即是编译成功：

4、运行程序

启动ROS核心程序：

roscore

新建一个终端，进入工作空间，注册程序：

cd ~/catkin_ws
source ./devel/setup.bash

运行talker.cpp

rosrun beginner_tutorials talker

会看见如下信息：

[ INFO] [1586177568.629530314]: hello world 0
[ INFO] [1586177568.729966014]: hello world 1
[ INFO] [1586177568.829701867]: hello world 2
[ INFO] [1586177568.930666243]: hello world 3
[ INFO] [1586177569.030527168]: hello world 4
[ INFO] [1586177569.129997647]: hello world 5
[ INFO] [1586177569.230753908]: hello world 6
[ INFO] [1586177569.330438986]: hello world 7
[ INFO] [1586177569.430001067]: hello world 8
[ INFO] [1586177569.529715160]: hello world 9

再新建一个终端，运行listener.cpp

rosrun beginner_tutorials listener

会看见如下信息：

[INFO] [WallTime: 1314931969.258941] /listener_17657_1314931968795I heard hello world 1314931969.26
[INFO] [WallTime: 1314931970.262246] /listener_17657_1314931968795I heard hello world 1314931970.26
[INFO] [WallTime: 1314931971.266348] /listener_17657_1314931968795I heard hello world 1314931971.26
[INFO] [WallTime: 1314931972.270429] /listener_17657_1314931968795I heard hello world 1314931972.27
[INFO] [WallTime: 1314931973.274382] /listener_17657_1314931968795I heard hello world 1314931973.27
[INFO] [WallTime: 1314931974.277694] /listener_17657_1314931968795I heard hello world 1314931974.28
[INFO] [WallTime: 1314931975.283708] /listener_17657_1314931968795I heard hello world 1314931975.28

到这里程序就没有问题了

二、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、创建功能包

cd ~/catkin_ws/src
catkin_create_pkg lesson2_homework std_msgs rospy roscpp

2、在工程包目录下的src目录中创建turtle_control.cpp文件

turtle_control.cpp

#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;
}

3、在lesson2_homework目录下的CmakeLists.txt文件中添加依赖项

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

4、在功能包目录下新建一个launch文件夹，在里面新建文件turtle_control.launch

launch文件内容如下：

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

5、编译

cd ~/catkin_ws
catkin_make

6、运行程序

新建终端启动ROS核心程序

roscore

再新建一个终端运行程序

source ./devel/setup.bash
rosrun lesson2_homework turtle_control

再次新建终端运行turtlesim.node节点

source ./devel/setup.bash
rosrun turtlesim turtlesim.node

最终运行结果如下，终端中会打印小海龟的实时坐标：

到这里任务就顺利完成啦！