ROS 懶人筆記 3 — 以C++撰寫Publisher與Subscriber

Publisher 的撰寫 (C++)

src/talker.cpp

總結所有步驟：

• 加入ROS公用的header與使用的的message header

#include "ros/ros.h"
#include "std_msgs/String.h"

• 初始化並指定node名稱

ros::init(argc, argv, "talker");

• 建立node的”握把“ (handle) 與 Publisher物件

ros::NodeHandle n;
ros::Publisher chatter_pub = n.advertise<std_msgs::String>("chatter", 1000);

• 設定publish頻率

ros::Rate loop_rate(10);

• 撰寫publish區段

while(ros::ok())
{
  std_msgs::Strings msg;
  //...
  chatter_pub.publish(msg);
ros::spinOnce();
loop_rate.sleep();
}

Subscriber 的撰寫 (C++)

src/listener.cpp

總結所有步驟：

• 加入ROS公用的header與使用的的message header

#include "ros/ros.h"
#include "std_msgs/String.h"

• 初始化並指定node名稱

ros::init(argc, argv, "listener");

• 建立node的”握把“ (handle) 、Subscribe物件與對應的回呼函式名

ros::NodeHandle n;
ros::Subscriber sub = n.subscribe("chatter", 1000, chatterCallback);

• 使用ros::spin()或ros::spinOnce()進行回呼函式呼叫

ros::spin()

• 於主函式外，撰寫subscribe的回呼函式，參數設定為訂閱message的常數指標參考

void chatterCallback(const std_msgs::String::ConstPtr& msg)
{  
  // do anything you want ...
  ROS_INFO("I heard: [%s]", msg->data.c_str());
}

最後記得要修改package.xml與CMakeLists.txt

• package.xml 中uncomment以下兩行

<build_depend>message_generation</build_depend>
<exec_depend>message_runtime</exec_depend>

• CMakeLists.txt 中，記得先加入message相關的指令(參考連結)，之後在於最底下加入建立執行檔、連結函式庫與新增相依項目的指令

執行publisher與subscriber (使用rosrun)

• 先啟動master node

roscore

• 以source指令設定環境

# In your catkin workspace
$ cd ~/catkin_ws
$ source ./devel/setup.bash

• 以rosrun執行beginner_tutorials package中的publisher (在此名稱為talker)

$ rosrun beginner_tutorials talker
[INFO] [WallTime: 1314931831.774057] hello world 1314931831.77 [INFO] [WallTime: 1314931832.775497] hello world 1314931832.77 [INFO] [WallTime: 1314931833.778937] hello world 1314931833.78 [INFO] [WallTime: 1314931834.782059] hello world 1314931834.78 [INFO] [WallTime: 1314931835.784853] hello world 1314931835.78 [INFO] [WallTime: 1314931836.788106] hello world 1314931836.79
...

• 以rosrun執行beginner_tutorials package中的subscriber (在此名稱為listener)

$ rosrun beginner_tutorials listener
[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
...

Reference :

• ROS官方教學 http://wiki.ros.org/ROS/Tutorials/
• Prof. Dr. Marco Hutter Programming for Robotics Introduction to ROS http://www.rsl.ethz.ch/education-students/lectures/ros.html