0、引言

  笔者因研究课题涉及ROS开发，学习了古月居出品的ROS入门21讲，为巩固ti坐标系的知识，本文将ROS的坐标系管理系统和tf坐标系广播与监听两讲内容进行总结。
  

1、机器人中的坐标变换

  （1）安装tf功能包；

//melodic指ubuntu18.04版本的ros
sudo apt-get install ros-melodic-turtle-tf

  
  注：其他ubuntu版本对应ros版本可查看【ROS如何进行开发？】。
  （2）启动tf包；

roslaunch turtle_tf turtle_tf_demo.launch

  
  （3）打开小海龟键盘控制；

rosrun turtlesim turtle_teleop_key

  
  通过键盘控制小海龟移动，另一个海龟跟随移动。
  
  （4）tf可视化工具；

//新建终端
rosrun tf view_frames

  
  （5）查看坐标系相对变换，命令行工具；

rosrun tf tf_echo turtle1 turtle2

  
  （6） tf三维可视化工具。

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

  ①打开RViz；
  
  ②键盘控制小海龟运动，同时RViz中显示坐标关系。
  

2、tf坐标系广播和监听

  （1）创建tf功能包；

cd ~/catkin_ws/srccatkin_create_pkg learning_tf roscpp rospy tf turtlesim

  
  （2）创建广播代码文件；
  在新建的功能包下src中打开新终端，并键入：gedit turtle_tf_broadcaster.cpp，输入以下代码并保存。

/*
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;
};

  
  （3）创建监听代码文件；
  在新建的功能包下src中打开新终端，并键入：gedit turtle_tf_listener.cpp，输入以下代码并保存。

/*
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;
};

  
  （4）在CMakeLists.txt中添加编译规则；

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）编译代码并运行。
  ①编译并启动roscore；

cd ~/catkin_wscatkin_make
或
catkin_make_isolatedsource devel/setup.bash
或
source devel_isolated/setup.bashroscore

  
  ②启动海龟结点；

//新建终端
rosrun turtlesim turtlesim_node

  
  ③广播海龟1消息；

//新建终端
source devel/setup.bash
或
source devel_isolated/setup.bash
rosrun learning_tf turtle_tf_broadcaster __name:=turtle1_tf_broadcaster /turtle1

  
  ④广播海龟2消息；

//新建终端
source devel/setup.bash
或
source devel_isolated/setup.bash
rosrun learning_tf turtle_tf_broadcaster __name:=turtle2_tf_broadcaster /turtle2

  
  ⑤监听海龟坐标变换关系并发布；

//新建终端
source devel/setup.bash
或
source devel_isolated/setup.bash
rosrun learning_tf turtle_tf_listener

  
  ⑥启动海龟键盘结点，移动海龟，使另一个海龟跟随移动。

//新建终端
rosrun turtlesim turtle_teleop_key

参考资料：
[1] 古月居GYH. 【古月居】古月·ROS入门21讲 | 一学就会的ROS机器人入门教程; 2019-07-16 [accessed 2023-04-09].
[2] cacrle. ROS如何进行开发？; 2023-04-09 [accessed 2023-04-09].