古月居ROS入门21讲-坐标系管理

视频链接：bilibili 搜 古月居
源代码：关注古月居公众号，回复ROS入门21讲

1 TF坐标变换

实现方式：广播TF变换，监听TF变换
roslaunch用于启动launch文件，launch相当于一个多节点启动的脚本文件

1.1 常用工具

17讲11分

1.终端1 运行launch文件
roslaunch turtle_tf turtle_tf_demo.launch 
2.终端2 控制小海龟
rosrun turtlesim turtle_teleop_key
3.1 终端3 可视化各个坐标系间关系，生成pdf文档显示tf tree
rosrun tf view_frames
3.2 获取任意两个坐标系间位置关系，给出两坐标系间平移和旋转数值
rosrun tf tf_echo tf_name1 tf_name2
3.3 三维直观显示坐标系间关系
rosrun rviz rviz -d 'rospack find turtle_tf' /rviz/turtle_rviz.rviz
# RVIZ工具中Fixed Frame选world
# 左下角点[Add]选择TF添加进来

2 tf坐标系广播与监听的编程实现

2.1 创建功能包

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

2.2 创建tf广播器代码（C++）

/***********************************************************************
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;
	//设置平移
	transform.setOrigin( tf::Vector3(msg->x, msg->y, 0.0) );
	tf::Quaternion q;
	q.setRPY(0, 0, msg->theta);
	//设置旋转
	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;
};

2.3 创建tf监听器代码（C++）

/***********************************************************************
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;

	// service编程，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);

	// topic编程，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;
};

2.4 编译与运行

添加cmake指令

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})

编译

catkin_make

运行

1. 终端1
roscore
2. 终端2
rosrun turtlesim turtlesim_node
3. 终端3,产生坐标系 /turtle1，获取 /turtle1和world坐标系间关系
rosrun learning_tf turtle_tf_broadcaster __name:=turtle1_tf_broadcaster /turtle1
__name:=turtle1_tf_broadcaster用于重映射到2.2中my_tf_broadcaster节点上，防止节点重名
4. 终端4，生坐标系 /turtle2，获取 /turtle2和world坐标系间关系
rosrun learning_tf turtle_tf_broadcaster __name:=turtle2_tf_broadcaster /turtle2
创建海龟2并且向海龟1运动
5. 终端5
rosrun learning_tf turtle_tf_listener
6. 终端6
rosrun turtlesim turtle_teleop_key