geometry_msgs::msg::Pose \\\\& start

这是一个 C++ 变量声明，它声明了一个名为 `start` 的变量，该变量是 `geometry_msgs::msg::Pose` 类型的引用。这意味着 `start` 可以引用（或指向） `geometry_msgs::msg::Pose` 类型的对象，而不是创建一个新的对象。在使用这个变量之前，需要确保它已经被初始化，或者引用的对象已经被创建并分配了内存空间。

相关问题

#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。

将下段代码转成python程序“#include <ros/ros.h> #include <tf/transform_listener.h> #include <geometry_msgs/Pose2D.h> #include <fstream> #include <iostream> #include <cmath> using namespace std; double x,y,z, qx,qy,qz, qw; double theta; geometry_msgs::Pose2D pos_now; int main(int argc, char** argv){ ros::init(argc, argv, "tf_Pose_Publisher"); ros::NodeHandle node; ros::Publisher _pose_pub=node.advertise<geometry_msgs::Pose2D>("pose_data", 10); tf::StampedTransform transform; tf::TransformListener listener; ros::Rate rate(10.0); while (ros::ok()){ ros::Time start = ros::Time::now(); cout << "StartTime:"<< start << endl; tf::StampedTransform transform; try{ //得到坐map和坐标base_link之间的关系 listener.waitForTransform("map","base_link", ros::Time(0), ros::Duration(3.0)); listener.lookupTransform("map", "base_link", ros::Time(0), transform); } catch (tf::TransformException &ex) { ROS_ERROR("%s",ex.what()); ros::Duration(1.0).sleep(); } x=transform.getOrigin().x(); y=transform.getOrigin().y(); z=transform.getOrigin().z(); tf::Quaternion q = transform.getRotation(); qx = q.x(); qy = q.y(); qz = q.z(); qw = q.w(); pos_now.x = transform.getOrigin().x(); pos_now.y =transform.getOrigin().y(); pos_now.theta = tf::getYaw(q); _pose_pub.publish(pos_now); printf("x: %f, y: %f, z: %f, qx: %f,qy: %f,qz: %f, qw: %f, theta: %f\n",x,y,z,qx,qy,qz,qw,pos_now.theta); rate.sleep(); ros::Time end = ros::Time::now(); cout << "EndTime:"<<end << endl; } return 0; };

以下是将C++代码转换为Python代码的结果：

#!/usr/bin/env python

import rospy
import tf
from geometry_msgs.msg import Pose2D

x, y, z, qx, qy, qz, qw = 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0
theta = 0.0
pos_now = Pose2D()

rospy.init_node('tf_Pose_Publisher')
_pose_pub = rospy.Publisher('pose_data', Pose2D, queue_size=10)
listener = tf.TransformListener()
rate = rospy.Rate(10.0)

while not rospy.is_shutdown():
    start = rospy.Time.now()
    print("StartTime: {}".format(start))
    try:
        # 得到坐map和坐标base_link之间的关系
        listener.waitForTransform("map", "base_link", rospy.Time(0), rospy.Duration(3.0))
        (trans, rot) = listener.lookupTransform("map", "base_link", rospy.Time(0))
        x = trans[0]
        y = trans[1]
        z = trans[2]
        qx = rot[0]
        qy = rot[1]
        qz = rot[2]
        qw = rot[3]
        pos_now.x = trans[0]
        pos_now.y = trans[1]
        pos_now.theta = tf.transformations.euler_from_quaternion(rot)[2]
        _pose_pub.publish(pos_now)
        print("x: {}, y: {}, z: {}, qx: {}, qy: {}, qz: {}, qw: {}, theta: {}".format(x, y, z, qx, qy, qz, qw, pos_now.theta))
    except (tf.LookupException, tf.ConnectivityException, tf.ExtrapolationException):
        rospy.sleep(1.0)
    rate.sleep()
    end = rospy.Time.now()
    print("EndTime: {}".format(end))