ROS话题与服务编程：控制小乌龟画圆，并且通过代码订阅小乌龟的实时位置并在终端打印

ROS话题与服务编程：控制小乌龟画圆，并且通过代码订阅小乌龟的实时位置并在终端打印

1.创建文件

进入src路径中创建yuan.cpp，代码如下：

include "ros/ros.h"

include "std_msgs/String.h"

include<geometry_msgs/Twist.h> //运动速度结构体类型 geometry_msgs::Twist的定义文件

int main(int argc, char *argv[])
{
ros::init(argc, argv, "vel_ctrl"); //对该节点进行初始化操作
ros::NodeHandle n; //申明一个NodeHandle对象n，并用n生成一个广播对象vel_pub
ros::Publisher vel_pub = n.advertise<geometry_msgs::Twist>("/turtle1/cmd_vel", 10);
ros::Publisher chatter_pub = n.advertise<std_msgs::String>("chatter", 1000);
ros::Rate loop_rate(10);
//vel_pub会在主题"/turtle1/cmd_vel"(机器人速度控制主题)里广播geometry_msgs::Twist类型的数据
//ros::Rate loopRate(2);
ROS_INFO("draw_circle start...");//输出显示信息
while(ros::ok())
{
geometry_msgs::Twist vel_cmd; //声明一个geometry_msgs::Twist 类型的对象vel_cmd，并将速度的值赋值到这个对象里面

vel_cmd.linear.x = 2.0;//前后（+-） m/s
vel_cmd.linear.y = 0.0; //左右（+-） m/s
vel_cmd.linear.z = 0.0;

vel_cmd.angular.x = 0;
vel_cmd.angular.y = 0;
vel_cmd.angular.z = 1.8; //机器人的自转速度，+左转，-右转，单位是rad/s

vel_pub.publish(vel_cmd); //赋值完毕后，发送到主题"/turtle1/cmd_vel"。机器人的核心节点会从这个主题接受发送过去的速度值，并转发到硬件体上去执行
std_msgs::String msg;
std::stringstream ss;//定义输出流对象
ss <<vel_cmd;
msg.data = ss.str();
/**
* The publish() function is how you send messages. The parameter
* is the message object. The type of this object must agree with the type
* given as a template parameter to the advertise<>() call, as was done
* in the constructor above.
*/
chatter_pub.publish(msg);
ros::spinOnce();//调用此函数给其他回调函数得以执行(比例程未使用回调函数)
//loopRate.sleep();
}
return 0;

}

位置不变，再创建一个callBackYuan.cpp，代码如下：

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("it is location: [%s]", msg->data.c_str());
  }

int main(int argc, char argv)
{
/

• The ros::init() function needs to see argc and argv so that it can perform

• any ROS arguments and name remapping that were provided at the command line. For programmatic

• remappings you can use a different version of init() which takes remappings

• directly, but for most command-line programs, passing argc and argv is the easiest

• way to do it. The third argument to init() is the name of the node.

• You must call one of the versions of ros::init() before using any other

• part of the ROS system.
  */
  ros::init(argc, argv, "yuan");

  /**

• NodeHandle is the main access point to communications with the ROS system.

• The first NodeHandle constructed will fully initialize this node, and the last

• NodeHandle destructed will close down the node.
  */
  ros::NodeHandle n;

  /**

• The subscribe() call is how you tell ROS that you want to receive messages

• on a given topic. This invokes a call to the ROS

• master node, which keeps a registry of who is publishing and who

• is subscribing. Messages are passed to a callback function, here

• called chatterCallback. subscribe() returns a Subscriber object that you

• must hold on to until you want to unsubscribe. When all copies of the Subscriber

• object go out of scope, this callback will automatically be unsubscribed from

• this topic.

• The second parameter to the subscribe() function is the size of the message

• queue. If messages are arriving faster than they are being processed, this

• is the number of messages that will be buffered up before beginning to throw

• away the oldest ones.
  */
  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;
  }

2.修改CMakeLists.txt

打开CMakeLists.txt，在末尾添加如下代码：

add_executable(yuan src/yuan.cpp)

target_link_libraries(yuan ${catkin_LIBRARIES})

add_dependencies(yuan comm_generate_messages_cpp)

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

接着返回工作空间编译一次

catkin_make

3.运行程序

打开四个终端依次输入命令运行，结果图如下