ros hello world 实现

转自http://blog.csdn.net/liulj95/article/details/47680599

最近老板安排任务，要把ROS框架在ARM+FPGA平台上实现。但是使用ROS创建程序步骤繁琐，所以这次将官方文档上面的Demo简化写下来，方便以后查看。

ROS版本：Hydro

Linux版本：Ubuntu12.04

在开始第一个ROS(Robot Operating System)程序之前，确保已经按照官方教程（点击打开链接）成功安装了ROS。本文建立的是一个非常简单的发布（Publisher）、订阅(Subscriber)程序。

创建一个工作区（workspace）

工作区可以作为一个独立的项目进行编译，存放ROS程序的源文件、编译文件和执行文件。建立工作区的方法如下：

 $ mkdir -p ~/catkin_ws/src
 $ cd ~/catkin_ws/src
 $ catkin_init_workspace

虽然这时候工作区是空的，但是我们依然可以进行编译：

 $ cd ~/catkin_ws/
 $ catkin_make

这时候，会在当前文件夹下生成devel，build这两个子文件夹，在devel文件夹下能看到几个setup.*sh文件。

接下来把工作区在bash中注册

 $ source devel/setup.bash

要验证是否已经在bash中注册可以使用如下命令：

 $ echo $ROS_PACKAGE_PATH
 /home/youruser/catkin_ws/src:/opt/ros/indigo/share:/opt/ros/indigo/stacks

如果能看到自己工作区的文件路径就说明已经成功了。

创建一个ROS工程包（Package）

在一个工作区内，可能会包含多个ROS工程包。而最基本ROS工程包中会包括CmakeLists.txt和Package.xml这两个文件，其中Package.xml中主要包含本项目信息和各种依赖（depends），而CmakeLists.txt中包含了如何编译和安装代码的信息。

首先切换到工作区：

 $ cd ~/catkin_ws/src

现在可以使用catkin_create_pkg命令去创建一个叫beginner_tutorials的包，这个包依靠std_msgs、roscpp、rospy。

 $ catkin_create_pkg beginner_tutorials std_msgs rospy roscpp

接下来在工作区编译这个工程包。

 $ cd ~/catkin_ws
 $ catkin_make

一个简单的发布（Publisher）、订阅(Subscriber)程序

写一个发布（Publisher）节点

节点（node）是连接到ROS网络中可执行的基本单元。我们在这创建一个发布者---“talker”节点，这个节点持续对外发布消息。

首先我们要把目录切换到我们的beginner_tutorials工程包中

 $ cd ~/catkin_ws/src/beginner_tutorials

因为我们已经编译过这个工程包了，所以会在beginner_tutorials文件夹下看到CmakeList.txt、package.xml文件和include、src这两个目录。接下来进入src子目录

 $ cd src

在src目录中创建一个talker.cpp文件，里面的内容如下：

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

 #include
 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, "talker");

   /**
    * 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 advertise() function is how you tell ROS that you want to
    * publish on a given topic name. This invokes a call to the ROS
    * master node, which keeps a registry of who is publishing and who
    * is subscribing. After this advertise() call is made, the master
    * node will notify anyone who is trying to subscribe to this topic name,
    * and they will in turn negotiate a peer-to-peer connection with this
    * node.  advertise() returns a Publisher object which allows you to
    * publish messages on that topic through a call to publish().  Once
    * all copies of the returned Publisher object are destroyed, the topic
    * will be automatically unadvertised.
    *
    * The second parameter to advertise() is the size of the message queue
    * used for publishing messages.  If messages are published more quickly
    * than we can send them, the number here specifies how many messages to
    * buffer up before throwing some away.
    */
   ros::Publisher chatter_pub = n.advertise("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());

     /**
      * 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();

     loop_rate.sleep();
     ++count;
   }


   return 0;
 }

写一个订阅（Subscriber）节点

还是在src目录下，创建一个listener.cpp文件。内容如下：

 #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("I heard: [%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, "listener");

   /**
    * 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;
 }

编译创建的节点
在编译我们创建的节点之前，我们还需要编辑Cmakelist.txt文件（注意：是beginner_tutorials项目包下的CMakelist文件），告诉编辑器我们需要编辑什么文件，需要什么依赖。

 $ gedit CMakeLists.txt

在文件末尾添加如下语句：

 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)

将目录切换到工作区目录，并执行catkin_make运行命令：

 $ cd ~/catkin_ws
 $ catkin_make

不出意外的话，会出现如下界面：

至此，程序已经创建完成，而接下来我们要检查一下我们创建的程序是否正确。

测试程序的正确性

首先，我们得要启动ROS核心程序roscore。

 $ roscore

在使用我们的程序之前，需要先把程序注册

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

运行talker节点：

 $ rosrun beginner_tutorials talker

这时候会看到如下信息：

 [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

这就表示发布（Publisher）节点已经正确的运行了。

接下来运行listener节点：

 $ rosrun beginner_tutorials listener

这时候会看到如下信息：

 [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

这说明订阅节点（listener）已经成功的接收到了发布节点（talker）发布的信息。至此，整个程序结束！

----------------------------------------分割线---------------------------------------------------------------------------

rosrun rqt_graphrqt_graph 

手动向rostopic /chatter 发送数据