ROS-TF-监听

前言：监听第一只海龟的位置，然后让第二只海龟跟随第一只海龟。

一、新建cpp文件

新建turtle_tf_listener.cpp文件，内容如下：

#include <ros/ros.h>
#include <tf/transform_listener.h>
#include <geometry_msgs/Twist.h>
#include <turtlesim/Spawn.h>

int main(int argc, char** argv){
  ros::init(argc, argv, "my_tf_listener");

  ros::NodeHandle node;

  ros::service::waitForService("spawn");
  ros::ServiceClient add_turtle =
    node.serviceClient<turtlesim::Spawn>("spawn");
  turtlesim::Spawn srv;
  add_turtle.call(srv);

  ros::Publisher turtle_vel =
    node.advertise<geometry_msgs::Twist>("turtle2/cmd_vel", 10);

  tf::TransformListener listener;

  ros::Rate rate(10.0);
  while (node.ok()){
    tf::StampedTransform transform;
    try{
      listener.lookupTransform("/turtle2", "/turtle1",
                               ros::Time(0), transform);
    }
    catch (tf::TransformException &ex) {
      ROS_ERROR("%s",ex.what());
      ros::Duration(1.0).sleep();
      continue;
    }

    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;
};

二、修改launch文件

在launch文件末尾添加

<launch>
    <!-- Turtlesim Node-->
    <node pkg="turtlesim" type="turtlesim_node" name="sim"/>

    <node pkg="turtlesim" type="turtle_teleop_key" name="teleop" output="screen"/>
    <!-- Axes -->
    <param name="scale_linear" value="2" type="double"/>
    <param name="scale_angular" value="2" type="double"/>

    <node pkg="learning_tf" type="turtle_tf_broadcaster"
          args="/turtle1" name="turtle1_tf_broadcaster" />
    <node pkg="learning_tf" type="turtle_tf_broadcaster"
          args="/turtle2" name="turtle2_tf_broadcaster" />
    <node pkg="learning_tf" type="turtle_tf_listener"
          name="listener" />
  </launch>

三、运行

roslaunch learning_tf start_demo.launch

-END-