18.tf坐标系广播与监听的实现

学习视频：https://www.bilibili.com/video/BV1zt411G7Vn?p=18
广播器代码：获取海龟位置，广播world与海龟坐标系之间的tf数据
监听器代码：监听tf数据，并计算、发布turtle2的速度指令
一、创建功能包

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

二、用C++创建tf广播器和监听者代码
1.tf广播器程序的创建
输入指令，打开turtle_tf_broadcaster.cpp文件

gedit ~/catkin_ws/src/learning_tf/src/turtle_tf_broadcaster.cpp

/***********************************************************************
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) );   //设置平移参数
	tf::Quaternion q;
	q.setRPY(0, 0, msg->theta);     //设置旋转参数
	transform.setRotation(q);       //保存至transform内部

	// 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;
};

2.tf监听器程序的创建
输入指令，打开turtle_tf_listener.cpp文件

gedit ~/catkin_ws/src/learning_tf/src/turtle_tf_listener.cpp

/***********************************************************************
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turtle2
	ros::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);  //设置频率
	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));  //等待变换   ros::Time(0) 查询当前时间   ros::Duration(3.0)等待时间
			listener.lookupTransform("/turtle2", "/turtle1", ros::Time(0), transform);    //执行变化   结果保存至transform变量中
		}
		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;
};

3.配置tf广播器与监听器代码编译规则

输入指令，打开CMakeList.txr文件

gedit ~/catkin_ws/src/learning_tf/CMakeLists.txt

加入下面代码如下图所示

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})

4.编译功能包

cd ~/catkin_ws/
catkin_make

三、用Python创建tf广播器和监听者代码
1.创建tf广播器代码
输入指令，打开turtle_tf_broadcaster.py文件。

mkdir ~/catkin_ws/src/learning_tf/scripts
gedit ~/catkin_ws/src/learning_tf/scripts/turtle_tf_broadcaster.py

#!/usr/bin/env python3
# -*- 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::Person

import roslib
roslib.load_manifest('learning_tf')
import rospy

import tf
import turtlesim.msg

def 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()

设置turtle_tf_broadcaster.py 文件运行权限

cd ~/catkin_ws/src/learning_tf/scripts
chmod +x turtle_tf_broadcaster.py 

2.创建tf监听者代码
输入指令，打开turtle_tf_listener.py文件。

gedit ~/catkin_ws/src/learning_tf/scripts/turtle_tf_listener.py

#!/usr/bin/env python3
# -*- 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::Person

import roslib
roslib.load_manifest('learning_tf')
import rospy
import math
import tf
import geometry_msgs.msg
import turtlesim.srv

if __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):
            continue

        angular = 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 = linear
        cmd.angular.z = angular
        turtle_vel.publish(cmd)

        rate.sleep()

设置turtle_tf_listener.py 文件运行权限

cd ~/catkin_ws/src/learning_tf/scripts
chmod +x turtle_tf_listener.py 

四、运行程序
1.运行roscore

roscore

2.打开新的终端，运行小海龟仿真器

rosrun turtlesim turtlesim_node 

3.打开新的终端，运行指令，发布turtle1和world之间关系

rosrun learning_tf turtle_tf_broadcaster __name:=turtle1_tf_broadcaster /turtle1

这里的/turtle1的第一个小海龟名
__name:=turtle1_tf_broadcaster：是ros里面重映射的一种机制，程序中的my_tf_broadcaster变为turtle1_tf_broadcaster，避免资源的冲突。
4.打开新的终端，运行指令，发布turtle2和world之间的关系

rosrun learning_tf turtle_tf_broadcaster __name:=turtle2_tf_broadcaster /turtle2

5.打开新的终端，运行指令，创建海龟2

rosrun learning_tf turtle_tf_listener

6.打开新的终端，运行指令，通过键盘控制海龟1

rosrun turtlesim turtle_teleop_key

7.运行效果

用python运行时会有报错

下一节用launch启动文件会避免此处错误。