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

这是一个指向 `geometry_msgs::msg::Pose` 类型对象的引用，命名为 `start`。这个对象包含了一个三维空间中的位姿信息，包括位置和方向。在ROS中，`geometry_msgs::msg::Pose` 类型经常用于表示机器人或物体的位姿信息。通过引用这个对象，你可以访问和修改其中的成员变量，比如位置和方向。

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 (dist >= 2.0) { twist_msg.linear.x = 0.0; ROS_INFO("Stop and Completed!"); twist_pub.publish(twist_msg); // Publish command ros::shutdown(); return; } 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; }请问该程序如何修改可使得乌龟按照正方形轨迹运行

要使乌龟按照正方形轨迹运行，你需要对代码进行修改。以下是修改的建议：

1. 在poseCallback函数中，添加一个新的静态变量来跟踪乌龟移动的边数和当前边的长度。例如：

static int side_count = 0;
static float side_length = 0.0;

2. 在计算距离的代码后面，添加以下代码来检查是否达到了一个边的长度：

// Check if turtle has reached the length of a side
if (dist >= side_length) {
  twist_msg.linear.x = 0.0;
  twist_msg.angular.z = 1.57; // Rotate the turtle by 90 degrees
  side_count++; // Increment the side count
  
  if (side_count % 4 == 0) {
    ROS_INFO("Stop and Completed!");
    twist_pub.publish(twist_msg); // Publish command
    ros::shutdown();
    return;
  }
  else {
    // Move the turtle forward again
    is_forward = true;
    x_start = pose.x;
    y_start = pose.y;
    theta_start = pose.theta;
    dist = 0.0;
  }
}

3. 在main函数中，添加以下代码来设置边的长度：

// Set the length of each side
side_length = 2.0;

这样修改后，乌龟将按照正方形轨迹运行，每条边的长度为2.0。当乌龟完成四个边时，程序将停止并关闭节点。请记得在发布命令之前将twist_msg.linear.y和twist_msg.linear.z设置为0.0，以确保乌龟只沿着x轴移动。

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))