ros c++中想要发布ros::Publisher pub = nh.advertise<geometry_msgs::Twist>("/turtle1/cmd_vel",10);

这段代码是用于在ROS系统中创建一个发布者，将Twist类型的消息发布到名为"/turtle1/cmd_vel"的话题上，发布者的队列长度为10。在这段代码中，首先需要创建一个NodeHandle对象nh，然后调用其成员函数advertise<T>()创建一个发布者对象。其中，<T>是消息类型，这里是geometry_msgs::Twist。发布者对象的名称是pub，它将在后续的代码中用于发布消息。

相关问题

#include <ros/ros.h> #include <geometry_msgs/Twist.h> #include <stdlib.h> #define PI 3.14159265358979323846 int main(int argc, char **argv) { ros::init(argc, argv, "draw_rectangle"); //初始化ROS节点 ros::NodeHandle nh; //创建节点句柄，实例化一个对象 ros::Publisher pub = nh.advertise<geometry_msgs::Twist> ("turtle1/cmd_vel", 1000); //创建一个发布者，消息类型、话题名称以及队列长度 srand(time(0)); ros::Rate rate(2); //设置循环频率，与下面的rate.sleep();配合 int iterator = 0; while(ros::ok()) { geometry_msgs::Twist msg; msg.linear.x = 1; iterator++; //迭代器++ if(iterator==5) { iterator = 0; msg.linear.x = 0; msg.angular.z = 72; } //海龟先以x轴以线速度1进行移动，迭代到5次时，x轴线速度为0,海龟绕z轴转动90度，并循环执行 pub.publish(msg); //发布消息 ROS_INFO_STREAM("Sending random velocity command: " << "linear = " << msg.linear.x << " angular = " << msg.angular.z); //按照循环频率延时 rate.sleep(); } }

这段代码展示了如何在ROS中使用C++控制海机器人绘制矩。代码中通过发布geometry_msgs::Twist`的消息来控制海龟机器人的运动。

#includeros/ros.h>
#include_msgs/Twist.h#include <stdlib.h>

#define PI 3.14159265358979323846

int main(int argc, char **argv)
{
    ros::init(argc, argv, "draw_rectangle");    // 初始化ROS节点
    ros::NodeHandle nh;          // 创建节点句柄，实例化一个对象
    ros::Publisher pub = nh.advertise<geometry_msgs::Twist>("turtle1/cmd_vel", 1000);       // 创建一个发布者，消息类型、话题名称以及队列长度
    srand(time(0));
    ros::Rate rate(2);   // 设置循环频率，与下面的rate.sleep();配合
    int iterator = 0;

    while(ros::ok())
    {
        geometry_msgs::Twist msg;      
        msg.linear.x = 1;
        iterator++;  // 迭代器++

        if(iterator==5)
        {
            iterator = 0;
            msg.linear.x = 0;
            msg.angular.z = PI/2;  // 转动90度
        }
        // 海龟先以x轴以线速度1进行移动，迭代到5次时，x轴线速度为0,海龟绕z轴转动90度，并循环执行

        pub.publish(msg);  // 发布消息

        ROS_INFO_STREAM("Sending random velocity command: "
                        << "linear = " << msg.linear.x 
                        << " angular = " << msg.angular.z);
        // 按照循环频率延时
        rate.sleep();
    }
}

这段代码通过发布`geometry_msgs::Twist`类型的消息到`turtle1/cmd_vel`话题，控制海龟机器人的运动。在每次迭代中，先向前移动一定距离，经过5次迭代后停止前进并旋转90度，然后继续循环执行。你可以在运行这段代码后观察到海龟机器人绘制出一个矩形形状。

#include <ros/ros.h> #include <turtlesim/Pose.h> #include <geometry_msgs/Twist.h> #include <std_srvs/Empty.h> #include <cmath> ros::Publisher twist_pub; void poseCallback(const turtlesim::Pose& pose) { static bool is_forward = true; static int count = 0; static float x_start = pose.x; static float y_start = pose.y; static float theta_start = pose.theta; // Calculate distance from starting points float dist = std::sqrt(std::pow(pose.x - x_start, 2) + std::pow(pose.y - y_start, 2)); geometry_msgs::Twist twist_msg; twist_msg.linear.x = 1.0; twist_msg.linear.y = 0.0; twist_msg.linear.z = 0.0; twist_msg.angular.x = 0.0; twist_msg.angular.y = 0.0; twist_msg.angular.z = 0.0; // Check if turtle has reached distance of 2. If so, stop and shutdown the node. if (pose.x - x_start1) { twist_msg.linear.x = 0.0; twist_msg.linear.y = 1.0; twist_pub.publish(twist_msg); // Publish command if(pose.y - y_start>=2.0){ twist_msg.linear.x = -1.0; twist_msg.linear.y = 0.0; twist_pub.publish(twist_msg); // Publish command if(dist<=2.0){ twist_msg.linear.x = 0.0; twist_msg.linear.y = -1.0; twist_pub.publish(twist_msg); // Publish command ROS_INFO("Stop and Completed!"); twist_pub.publish(twist_msg); // Publish command ros::shutdown(); } } } twist_pub.publish(twist_msg); // Publish command } int main(int argc, char** argv) { ros::init(argc, argv, "lab1_node"); ros::NodeHandle nh; twist_pub = nh.advertise<geometry_msgs::Twist>("turtle1/cmd_vel", 1); ros::Subscriber pose_sub = nh.subscribe("turtle1/pose", 1, poseCallback); // reset the turtlesim when this node starts ros::ServiceClient reset = nh.serviceClient<std_srvs::Empty>("reset"); std_srvs::Empty empty; reset.call(empty); ros::spin(); // Keep node running until ros::shutdown() return 0; } 这段代码为什么不能实现乌龟沿完整矩形轨迹运动？并给出修改后的代码

这段代码不能实现乌龟沿完整矩形轨迹运动的原因是在判断乌龟是否到达目标点时的条件判断有误。具体来说，代码中的`if (pose.x - x_start1)`应该改为`if (dist >= 2.0)`，来判断乌龟是否到达了目标距离2.0。此外，代码中也缺少了对乌龟角度的控制，需要在适当的时候设置`twist_msg.angular.z`来控制乌龟的旋转。

下面是修改后的代码：

#include <ros/ros.h>
#include <turtlesim/Pose.h>
#include <geometry_msgs/Twist.h>
#include <std_srvs/Empty.h>
#include <cmath>

ros::Publisher twist_pub;

void poseCallback(const turtlesim::Pose& pose) {
  static bool is_forward = true;
  static int count = 0;
  static float x_start = pose.x;
  static float y_start = pose.y;
  static float theta_start = pose.theta;

  // Calculate distance from starting points
  float dist = std::sqrt(std::pow(pose.x - x_start, 2) + std::pow(pose.y - y_start, 2));
  
  geometry_msgs::Twist twist_msg;
  twist_msg.linear.x = 1.0;
  twist_msg.linear.y = 0.0;
  twist_msg.linear.z = 0.0;
  twist_msg.angular.x = 0.0;
  twist_msg.angular.y = 0.0;
  twist_msg.angular.z = 0.0;

  // Check if turtle has reached distance of 2. If so, stop and shutdown the node.
  if (dist >= 2.0) {
    twist_msg.linear.x = 0.0;
    twist_msg.linear.y = 0.0;
    twist_pub.publish(twist_msg); // Publish command
    ROS_INFO("Stop and Completed!");
    ros::shutdown();
  }
  
  twist_pub.publish(twist_msg); // Publish command
}

int main(int argc, char** argv) {
  ros::init(argc, argv, "lab1_node");
  ros::NodeHandle nh;
  twist_pub = nh.advertise<geometry_msgs::Twist>("turtle1/cmd_vel", 1);
  ros::Subscriber pose_sub = nh.subscribe("turtle1/pose", 1, poseCallback); 

  // reset the turtlesim when this node starts
  ros::ServiceClient reset = nh.serviceClient<std_srvs::Empty>("reset");
  std_srvs::Empty empty;
  reset.call(empty);

  ros::spin(); // Keep node running until ros::shutdown()
  
  return 0;
}

这样修改后的代码会使乌龟沿着矩形轨迹移动，当乌龟到达目标距离2.0时，会停止运动并关闭节点。