古月居 ROS 入門21講--PA18 tf坐標系廣播與監聽的編程實現 1、創建功能包 cd ~/catkin_ws/src catkin_create_pkg learning_tf roscpp rospy tf turtlesim

2、創建 tf 廣播器代碼（C++）
$■$ 如何實現一個 tf 廣播器
$?$ 定義 TF 廣播器（TransformBroadcaster）
$?$ 創建坐標變換值
$?$ 發布坐標變換（sendTransform）

/*********************************************************************** Copyright 2020 GuYueHome (www.guyuehome.com). ***********************************************************************//*** 該例程產生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; };

3、如何實現一個 TF 監聽器
$?$ 定義 TF 監聽器（TransformListener）
$?$ 查找坐標變換（waitForTransform、lookTransform）

/*********************************************************************** Copyright 2020 GuYueHome (www.guyuehome.com). ***********************************************************************//*** 該例程監聽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，發布turtle2的速度控制指令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; };

4、配置 tf 廣播器與監聽器代碼編譯規則
$■$ 如何配置 CMakeLists.txt 中的編譯規則
$?$ 設置需要編譯的代碼和生成的可執行文件；
$?$ 設置鏈接庫；

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})

5、編譯并運行

cd ~/catkin_ws catkin_make source devel/setup.bash roscore rosrun turtlesim turtlesim_node rosrun learning_tf turtle_tf_broadcaster __name:=turtle1_tf_broadcaster /turtle1 //分別定義兩只小海龜名字 rosrun learning_tf turtle_tf_broadcaster __name:=turtle2_tf_broadcaster /turtle2 rosrun learning_tf turtle_tf_listener rosrun turtlesim turtle_teleop_key //控制小海龜

總結

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