安裝Ros中 tf 相關功能包

sudo apt-get install ros-melodic-turtle-tf

啟動launch文件，這個launch文件相當于一個腳本，可以一次性啟動很多節點

roslaunch turtle_tf turtle_tf_demo.launch

啟動海龜控制節點

rosrun turtlesim turtle_teleop_key

能夠監聽當前時刻所有通過ROS廣播的tf坐標系，并繪制出樹狀圖表示坐標系之間的連接關系保存到離線文件中，監聽5秒后，保存5秒內坐標系之間的關系，會生成一個pdf文件。

rosrun tf view_frames

使用tf_echo工具可以查看兩個廣播參考系之間的關系。

rosrun tf tf_echo [reference_frame] [target_frame]

例如：

rosrun tf tf_echo turtle1 turtle2

通過rvize可視化工具更加形象的看到這三者之間的關系。

rosrun rviz rviz -d 'rospack find turtle_tf' /rviz/turtle.rviz

---

cd ~/catkin_ws/src catkin_create_pkg learning_tf roscpp rospy tf turtlesim

如何實現一個tf廣播器

• 定義TF廣播器
• 創建坐標變換值
• 發布坐標變換

如何實現一個TF監聽器

• 定義TF監聽器
• 查找坐標變換

在創建的 learning_tf 目錄中的src文件夾下創建一個 cpp文件

cd ~/catkin_ws/src/learning_tf/src touch turtle_tf_broadcaster.cpp

在 turtle_tf_broadcaster.cpp 文件中寫入以下代碼。
以下代碼的功能：產生tf數據，并計算、發布turtle2的速度指令

#include <ros/ros.h> #include <tf/transform_broadcaster.h> #include <turtlesim/Pose.h>std::string turtle_name;void poseCallback(const turtlesim::PoseConstPtr& msg) {// 創建tf的廣播器static tf::TransformBroadcaster br;// 初始化tf數據tf::Transform transform;transform.setOrigin( tf::Vector3(msg->x, msg->y, 0.0) );tf::Quaternion q;q.setRPY(0, 0, msg->theta);transform.setRotation(q);// 廣播world與海龜坐標系之間的tf數據br.sendTransform(tf::StampedTransform(transform, ros::Time::now(), "world", turtle_name)); }int main(int argc, char** argv) {// 初始化ROS節點ros::init(argc, argv, "my_tf_broadcaster");// 輸入參數作為海龜的名字if (argc != 2){ROS_ERROR("need turtle name as argument"); return -1;}turtle_name = argv[1];// 訂閱海龜的位姿話題ros::NodeHandle node;ros::Subscriber sub = node.subscribe(turtle_name+"/pose", 10, &poseCallback);// 循環等待回調函數ros::spin();return 0; };

在創建的 learning_tf 目錄中的src文件夾下創建一個 cpp文件

cd ~/catkin_ws/src/learning_tf/src touch turtle_tf_listener.cpp

在 turtle_tf_listener.cpp 文件中寫入以下代碼。
以下代碼的功能：監聽tf數據，并計算、發布turtle2的速度指令

#include <ros/ros.h> #include <tf/transform_listener.h> #include <geometry_msgs/Twist.h> #include <turtlesim/Spawn.h>int main(int argc, char** argv) {// 初始化ROS節點ros::init(argc, argv, "my_tf_listener");// 創建節點句柄ros::NodeHandle node;// 請求產生turtle2ros::service::waitForService("/spawn");ros::ServiceClient add_turtle = node.serviceClient<turtlesim::Spawn>("/spawn");turtlesim::Spawn srv;add_turtle.call(srv);// 創建發布turtle2速度控制指令的發布者ros::Publisher turtle_vel = node.advertise<geometry_msgs::Twist>("/turtle2/cmd_vel", 10);// 創建tf的監聽器tf::TransformListener listener;ros::Rate rate(10.0);while (node.ok()){// 獲取turtle1與turtle2坐標系之間的tf數據tf::StampedTransform transform;try{listener.waitForTransform("/turtle2", "/turtle1", ros::Time(0), ros::Duration(3.0));listener.lookupTransform("/turtle2", "/turtle1", ros::Time(0), transform);}catch (tf::TransformException &ex) {ROS_ERROR("%s",ex.what());ros::Duration(1.0).sleep();continue;}// 根據turtle1與turtle2坐標系之間的位置關系，計算turtle2需要運動的線速度和角速度// 并發布速度控制指令，使turtle2向turtle1移動geometry_msgs::Twist vel_msg;vel_msg.angular.z = 4.0 * atan2(transform.getOrigin().y(),transform.getOrigin().x());vel_msg.linear.x = 0.5 * sqrt(pow(transform.getOrigin().x(), 2) +pow(transform.getOrigin().y(), 2));turtle_vel.publish(vel_msg);rate.sleep();}return 0; };

在CMakeLists.txt中添加以下代碼：

add_executable(turtle_tf_broadcaster src/turtle_tf_broadcaster.cpp) target_link_libraries(turtle_tf_broadcaster ${catkin_LIBRARIES})add_executable(turtle_tf_listener src/turtle_tf_listener.cpp) target_link_libraries(turtle_tf_listener ${catkin_LIBRARIES})

編譯項目

cd ~/catkin_ws catkin_make

設置環境變量，讓系統能夠找到該工作空間

source devel/setup.bash

啟動ROS Master

roscore

啟動小海龜仿真器

rosrun turtlesim turtlesim_node

發布/turtle1海龜坐標系關系

rosrun learning_tf turtle_tf_broadcaster __name:=turtle1_tf_broadcaster /turtle1

注：turtle_tf_broadcaster __name:=turtle1_tf_broadcaster 重新命名

發布/turtle2海龜坐標系關系

rosrun learning_tf turtle_tf_broadcaster __name:=turtle2_tf_broadcaster /turtle2

啟動自定義的節點

rosrun learning_tf turtle_tf_listener

啟動海龜控制節點

rosrun turtlesim turtle_teleop_key

---

用Python實現的步驟：

cd ~/catkin_ws/src/learning_tf

創建 scripts 文件夾

mkdir scripts cd scripts

創建 turtle_tf_broadcaster.py Python文件

touch turtle_tf_broadcaster.py

用Python實現的代碼：
以下代碼的功能：請求/show_person服務，服務數據類型learning_service::Person

#!/usr/bin/env python # -*- coding: utf-8 -*-import roslib roslib.load_manifest('learning_tf') import rospyimport tf import turtlesim.msgdef handle_turtle_pose(msg, turtlename):br = tf.TransformBroadcaster()br.sendTransform((msg.x, msg.y, 0),tf.transformations.quaternion_from_euler(0, 0, msg.theta),rospy.Time.now(),turtlename,"world")if __name__ == '__main__':rospy.init_node('turtle_tf_broadcaster')turtlename = rospy.get_param('~turtle')rospy.Subscriber('/%s/pose' % turtlename,turtlesim.msg.Pose,handle_turtle_pose,turtlename)rospy.spin()

創建 turtle_tf_listener.py Python文件

touch turtle_tf_listener.py

用Python實現的代碼：
以下代碼的功能：請求/show_person服務，服務數據類型learning_service::Person

#!/usr/bin/env python # -*- coding: utf-8 -*-import roslib roslib.load_manifest('learning_tf') import rospy import math import tf import geometry_msgs.msg import turtlesim.srvif __name__ == '__main__':rospy.init_node('turtle_tf_listener')listener = tf.TransformListener()rospy.wait_for_service('spawn')spawner = rospy.ServiceProxy('spawn', turtlesim.srv.Spawn)spawner(4, 2, 0, 'turtle2')turtle_vel = rospy.Publisher('turtle2/cmd_vel', geometry_msgs.msg.Twist,queue_size=1)rate = rospy.Rate(10.0)while not rospy.is_shutdown():try:(trans,rot) = listener.lookupTransform('/turtle2', '/turtle1', rospy.Time(0))except (tf.LookupException, tf.ConnectivityException, tf.ExtrapolationException):continueangular = 4 * math.atan2(trans[1], trans[0])linear = 0.5 * math.sqrt(trans[0] ** 2 + trans[1] ** 2)cmd = geometry_msgs.msg.Twist()cmd.linear.x = linearcmd.angular.z = angularturtle_vel.publish(cmd)rate.sleep()

注意：需要將Python設置為可執行文件。

啟動ROS Master

roscore

啟動小海龜仿真器

rosrun turtlesim turtlesim_node

發布/turtle1海龜坐標系關系

rosrun learning_tf turtle_tf_broadcaster.py __name:=turtle1_tf_badcaster _turtle:=turtle1

發布/turtle2海龜坐標系關系

rosrun learning_tf turtle_tf_broadcaster.py __name:=turtle2_tf_badcaster _turtle:=turtle2

啟動自定義的監聽節點

rosrun learning_tf turtle_tf_listener.py

啟動海龜控制節點

rosrun turtlesim turtle_teleop_key

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