ROS-TF-广播

前言：广播海龟移动中的实时位置。

一、新建功能包

在工作空间中新建learning_tf 功能包，依赖为tf roscpp rospy turtlesim

二、新建cpp文件

新建turtle_tf_broadcaster.cpp文件，文件内容如下：

#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;
};

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代码解释：

#include <tf/transform_broadcaster.h>，TF功能包提供了一个广播工具TransformBroadcaster，这个类需要引用<tf/transform_broadcaster.h>头文件

 tf::Transform transform;
  transform.setOrigin( tf::Vector3(msg->x, msg->y, 0.0) );
  tf::Quaternion q;
  q.setRPY(0, 0, msg->theta);

这里创建了一个变换实例，并将2D位姿信息转化为3D位姿信息。

transform.setRotation(q);

这里设置了旋转

br.sendTransform(tf::StampedTransform(transform, ros::Time::now(), "world", turtle_name));

使用TransformBroadcaster发送TF变换需要四个参数：

1. 变换本身
2. 时间戳
3. 提供连杆的父框架，这里是world
4. 提供连杆的子框架，这里是乌龟本身

三、新建launch文件

新建start_demo.launch文件，文件内容如下：

<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" />

  </launch>

运行launch文件

roslaunch learning_tf start_demo.launch

四、查看广播

rosrun tf tf_echo /world /turtle1

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