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ROS话题与服务编程:控制小乌龟画圆圈(旋转),并且通过代码订阅小乌龟的实时位置,并在终端打印
ROS话题编程是嵌入式开发学习的一项重要内容,只有学会ros的话题与服务编程,我们才能够继续往更深入的地方学习嵌入式的系统开发,本次博客,林君将带大家学习怎么控制乌龟画圆(旋转),并通过订阅服务实时在终端打印位置信息 一、进入我们的工程包,创建小乌龟画圆发送程序 1、新建一个终端,命名为终端1,然后进入我们的工程文件包 cd ~/ros/src/comm/src这里ros是林君自己的ros工作空间、comm是林君自己定义的工程包! 2、新建画圆程序名为yuan.cpp touch yuan.cpp 3、打开文件将如下代码写入yuan.cpp中:1)、打开文件如下命令 gedit yuan.cpp2)、写入文件中的代码如下命令: #include "ros/ros.h" #include "std_msgs/String.h" #include //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("/turtle1/cmd_vel", 10); ros::Publisher chatter_pub = n.advertise("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 /** * 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; } 3、关闭文件,到这里,我们小乌龟实时更新位置信息的文件也已经建立ok啦,如下所示:如下图所示: 如下图所示即为成功: 1)、回到我们的工作空间 cd ~/ros2)、程序注册 source ./devel/setup.bash1)、进入工作空间 cd ~/ros2)、程序注册 source ./devel/setup.bash
记住,我们新建的终端一个都不要关闭 1)、终端1运行画圆程序 rosrun comm yuan在该命令执行后,上面的终端3、窗口4都会发生变化,如下图所示: |
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