ros 用python开启节点 ros运行python程序

ROS中的程序称为节点（Node），每个节点实现特定的功能，通过节点之间相互通信从而实现完整的软件功能。从描述可以看出，这是分布式程序。

文章目录

• 一、创建工作区（workspace）

• 1.1 编译
• 1.2 验证工作区在bash中注册

• 二、ROS工程包（Package）

• 2.1 创建ros工程包
• 2.2 编译这个工程包

• 三、编写发布（Publisher）程序
• 四、编写订阅(Subscriber)程序
• 五、修改Cmakelist.txt
• 六、编译程序
• 七、运行程序

• 7.1 启动rosscore
• 7.2 运行talker节点
• 7.2 运行listener节点

根据链接，运行后的结果如下图所示：

一、创建工作区（workspace）

相当于IDE中的创建工程目录。工作区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。之后catkin_make就是在这里编译程序。

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

1.1 编译

虽然这时候工作区是空的，但是我们依然可以进行编译：
注意看哈，编译需要转到catkin_ws这个路径下，运行catkin_make。

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。

1.2 验证工作区在bash中注册

在catkin_ws文件夹路径下，运行source将工作区在bash中注册。这样之后rosrun运行程序时，就可以找到程序了，否则会rosrun启动程序失败。这里提前做一个验证工作。

source devel/setup.bash
echo $ROS_PACKAGE_PATH

打印如下信息，说明工作区可以成功在bash中注册。

二、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 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。

2.1 创建ros工程包

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。

cd ~/catkin_ws/src
catkin_create_pkg beginner_tutorials std_msgs rospy roscpp

2.2 编译这个工程包

参考上节的1.1小节。

三、编写发布（Publisher）程序

写一个发布（Publisher）节点。这个节点就是通信方式里的——Topic方式。
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。

cd ~/catkin_ws/src/beginner_tutorials/src
vi talker.cpp

在弹出的文本编辑框中输入如下：

#include "ros/ros.h"
#include "std_msgs/String.h"
 
#include <sstream>
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<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());
 
    /**
     * 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;
}

四、编写订阅(Subscriber)程序

同理，新建订阅Topic消息的节点。

#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;
}

五、修改Cmakelist.txt

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。
在Cmakelist.txt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)

六、编译程序

将目录切换到工作区目录，并执行catkin_make运行命令：正常的运行结果如下图。

cd ~/catkin_ws
catkin_make

七、运行程序

7.1 启动rosscore

首先我们得要启动ROS核心程序roscore。使用Ctrl+Alt+T新建一个终端，输入如下

roscore

7.2 运行talker节点

使用Ctrl+Alt+T新建一个终端，输入如下
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
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

7.2 运行listener节点

使用Ctrl+Alt+T新建一个终端，输入如下
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
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

至此，说明两个程序（节点Node）都运行成功了。