自己写一个ROS程序

ROS版本: kinetic
Linux版本:Ubuntu 15.10
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。

1 创建一个工作区(workspace)

    $ 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。

2 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：

[cpp] view plain copy

    #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。

[plain] view plain copy

$ gedit CMakeLists.txt

在文件末尾添加如下语句：

[plain] view plain copy

    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：

[plain] view plain copy

    $ 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
[plain] view plain copy

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

运行talker节点：
[plain] view plain copy

$ rosrun beginner_tutorials talker 

这时候会看到如下信息：

[plain] view plain copy

    [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：
[plain] view plain copy

$ rosrun beginner_tutorials listener  

这时候会看到如下信息：

[plain] view plain copy

    [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！