ROS1学习笔记：tf坐标系广播与监听的编程实现（ubuntu20.04）

参考B站古月居ROS入门21讲：tf坐标系广播与监听的编程实现
基于VMware Ubuntu 20.04 Noetic版本的环境

一、创建功能包

我们在src目录下创建learning_tf功能包：

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

二、创建代码

如何实现一个TF广播器？

• 定义TF广播器（TransformBroadcaster）
• 创建坐标变换值
• 发布坐标变换（sendTransform）

如何实现一个TF监听器？

• 定义TF监听器（TransformListener）
• 查找坐标变换（waitForTransform、lookupTransform）

2.1 以C++为例

turtle_tf_broadcaster.cpp和turtle_tf_listener.cpp拷贝进src目录下，
turtle_tf_broadcaster.cpp代码为：

/***********************************************************************
Copyright 2020 GuYueHome (www.guyuehome.com).
***********************************************************************//*** 该例程产生tf数据，并计算、发布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)
{// 创建tf的广播器static tf::TransformBroadcaster br;// 初始化tf数据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);// 广播world与海龟坐标系之间的tf数据br.sendTransform(tf::StampedTransform(transform, ros::Time::now(), "world", turtle_name));
}int main(int argc, char** argv)
{// 初始化ROS节点ros::init(argc, argv, "my_tf_broadcaster");// 输入参数作为海龟的名字if (argc != 2){ROS_ERROR("need turtle name as argument"); return -1;}turtle_name = argv[1];// 订阅海龟的位姿话题ros::NodeHandle node;ros::Subscriber sub = node.subscribe(turtle_name+"/pose", 10, &poseCallback);// 循环等待回调函数ros::spin();return 0;
};

turtle_tf_listener.cpp代码为：

/***********************************************************************
Copyright 2020 GuYueHome (www.guyuehome.com).
***********************************************************************//*** 该例程监听tf数据，并计算、发布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节点ros::init(argc, argv, "my_tf_listener");// 创建节点句柄ros::NodeHandle node;// 请求产生turtle2ros::service::waitForService("/spawn");ros::ServiceClient add_turtle = node.serviceClient<turtlesim::Spawn>("/spawn");turtlesim::Spawn srv;add_turtle.call(srv);// 创建发布turtle2速度控制指令的发布者ros::Publisher turtle_vel = node.advertise<geometry_msgs::Twist>("/turtle2/cmd_vel", 10);// 创建tf的监听器tf::TransformListener listener;ros::Rate rate(10.0);while (node.ok()){// 获取turtle1与turtle2坐标系之间的tf数据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;}// 根据turtle1与turtle2坐标系之间的位置关系，发布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;
};

2.1.1 配置代码编译规则

将以下代码拷贝CMakeLists.txt进指定位置：

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})

2.1.2 编译整个工作空间

cd ~/catkin_ws
catkin_make

2.1.2 配置环境变量

之前已经配置过。

2.1.4 执行代码

roscore

rosrun turtlesim turtlesim_node

我们下面直接在命令行传入参数。
第1个参数：我们在turtle_tf_broadcaster.cpp定义节点时使用了"my_tf_broadcaster"的名字，我们使用__name:=传入新的名字取代"my_tf_broadcaster"，这样避免名字重复（因为ROS中节点名字不能重复），这样就可以重复跑程序了。
第2个参数是turtle名称 turtle1 和 turtle2。

rosrun learning_tf turtle_tf_broadcaster __name:=turtle1_tf_broadcaster /turtle1

rosrun learning_tf turtle_tf_broadcaster __name:=turtle2_tf_broadcaster /turtle2

rosrun learning_tf turtle_tf_listener

执行完后就会有一只小海龟生成并跑向中间的第1只小海龟。

我们可以用键盘控制小海龟，同样可以让第2只小海龟追着我们跑。

2.2 以Python为例

将turtle_tf_broadcaster.py和turtle_tf_listener.py拷贝进scripts文件夹下(打开执行权限)。
turtle_tf_broadcaster.py代码为：

#!/usr/bin/env python
# -*- coding: utf-8 -*-########################################################################
####          Copyright 2020 GuYueHome (www.guyuehome.com).          ###
######################################################################### 该例程将请求/show_person服务，服务数据类型learning_service::Personimport 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()

turtle_tf_listener.py代码为：

#!/usr/bin/env python
# -*- coding: utf-8 -*-########################################################################
####          Copyright 2020 GuYueHome (www.guyuehome.com).          ###
######################################################################### 该例程将请求/show_person服务，服务数据类型learning_service::Personimport 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()

2.2.1 配置代码编译规则

打开CMakeLists.txt，配置编译规则

2.2.2 编译整个工作空间

cd ~/catkin_ws
catkin_make

2.2.3 配置环境变量

之前已经配置过。

2.2.4 执行代码

roscore

rosrun turtlesim turtlesim_node

rosrun learning_tf turtle_tf_broadcaster.py __name:=turtle1_tf_broadcaster _turtle:=turtle1

rosrun learning_tf turtle_tf_broadcaster.py __name:=turtle2_tf_broadcaster _turtle:=turtle2

rosrun learning_tf turtle_tf_listener.py

rosrun turtlesim turtle_teleop_key