ROS机器人操作系统

一、创建功能包

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

二、创建TF广播代码

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）
C++

 * 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;
};

Python

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# 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()

三、创建TF监听器

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）

/**
 * 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);
        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;
};

四、配置编译规则

将cpp文件编译成可执行文件

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})

五、编译并运行

$ 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
$ rosrun learning_tf turtle_tf_broadcaster __name:=turtle2_tf_broadcaster /turtle2
$ rosrun learning_tf turtle_tf_listener
$ rosrun turtlesim turtle_teleop_key

总结

这里是上一讲的底层代码。