a tf broadcaster

1.创建包

mkdir -p catkin_ws/src
cd catkin_ws/src
catkin_create_pkg learning_tf tf roscpp rospy turtlesim 

建立你的新包roscd之前：

cd ~/catkin_ws
catkin_make
source ./devel/setup.bash

这时功能包就已经构建完成了。
此时打开Roboware studio 在/learning_tf/src下编写TF广播器（turtle_tf_broadcaster.cpp ）：

#include <ros/ros.h>
#include <tf/transform_broadcaster.h>
#include <turtlesim/Pose.h>
 
std::string turtle_name;
 
 
 
void poseCallback(const turtlesim::PoseConstPtr& msg){
  static tf::TransformBroadcaster br;
  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);
  br.sendTransform(tf::StampedTransform(transform, ros::Time::now(), "world", turtle_name));
}
 
int main(int argc, char** argv){
  ros::init(argc, argv, "my_tf_broadcaster");
  if (argc != 2){ROS_ERROR("need turtle name as argument"); return -1;};
  turtle_name = argv[1];
 
  ros::NodeHandle node;
  ros::Subscriber sub = node.subscribe(turtle_name+"/pose", 10, &poseCallback);
 
  ros::spin();
  return 0;
};

需要说明的是，在创建cpp文件时应该是添加到可执行的文件这一选项。
打开CMakLists.txt文件，并添加以下行：

add_executable(turtle_tf_broadcaster src/turtle_tf_broadcaster.cpp)
target_link_libraries(turtle_tf_broadcaster ${catkin_LIBRARIES})

在/learning_tf/src下编写TF监听器（turtle_tf_listener.cpp）

#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;
};

打开CMakLists.txt文件，并添加以下行：

add_executable(turtle_tf_listener src/turtle_tf_listener.cpp)
target_link_libraries(turtle_tf_listener ${catkin_LIBRARIES})

在leanring_tf下创建launch文件：
mkdir launch
在roboware中创建launch文件start_demo.launch

<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>

保存好所有的文件后在终端中进入：

cd catkin_ws
catkin_make
source ./devel/setup.bash

然后再运行：

roslaunch learning_tf start_demo.launch

这时就可以看到两只turtle了，也就是最开始见到的跟随效果。