（五）ROS 发布tf消息并在rviz中显示

1.总体步骤介绍及实验结果

本文通过实现ROS中的示例来理解ROS中的坐标变换tf
参考的英文教程如下
http://wiki.ros.org/tf/Tutorials/Introduction%20to%20tf
以上的ROS教程有两只乌龟，比较麻烦。
本文将修改教程的程序，将两只乌龟变为一只乌龟，使理解TF的使用更加容易。
本程序实现的功能是使用键盘控制乌龟在TurtleSim中移动，然后通过turtlesim节点发送广播消息，最后在rviz中显示变换。

节点关系图如下

如图，可以分为几个步骤
（1）键盘节点teleop发送/turtle1/cmd_vel消息给 turtlesim节点，turtlesim节点解析命令并控制乌龟移动。
（2）turtlesim节点发送/turtle1/pose消息给my_turtle1_tf_broadcaster节点。
（3）my_turtle1_tf_broadcaster节点发送/tf消息。
（4）最后rviz解析/tf消息并显示，从而实现坐标变换可视化。
节点就是一个单一的进程，其中键盘控制节点和sim节点通过启动相应的包的节点来实现。本文主要阐述turtle1_tf_broadcaster节点的c++实现及通过rviz显示坐标变换的.rviz系统文件的配置。

2.示例的具体实现

1.启动teleop节点

rosrun turtlesim turtle_teleop_key

2.启动sim节点

rosrun turtlesim turtlesim_node

3.实现turtle1_tf_broadcaster，并启动learning_tf包下的turtle_tf_broadcaster节点

具体实现过程如
http://wiki.ros.org/tf/Tutorials/Writing%20a%20tf%20broadcaster%20%28C%2B%2B%29
主要是编辑turtle_tf_broadcaster.cpp代码并生成learning_tf包，注意节点的可执行文件名为turtle_tf_broadcaster
turtle_tf_broadcaster.cpp代码如下

#include 
#include 
#include 

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;
};

编译好turtle_tf_broadcaster后输入

rosrun learning_tf turtle_tf_broadcaster /turtle1

启动turtle_tf_broadcaster节点。
rqt_graph可以看到节点图如下

4.启动rqt_rviz工具显示坐标变换

rosrun rqt_rviz rqt_rviz

并加载配置文件,点击rqt_rviz的file菜单，open config 找到exampe_tf.rviz文件并打开。
用键盘控制，可以发现坐标在移动，实现了使用rviz显示坐标变换。
其中example_tf.rviz文件如下

Panels:
  - Class: rviz/Displays
    Help Height: 78
    Name: Displays
    Property Tree Widget:
      Expanded: ~
      Splitter Ratio: 0.616034
    Tree Height: 469
  - Class: rviz/Selection
    Name: Selection
  - Class: rviz/Tool Properties
    Expanded:
      - /2D Pose Estimate1
      - /2D Nav Goal1
      - /Publish Point1
    Name: Tool Properties
    Splitter Ratio: 0.588679
  - Class: rviz/Views
    Expanded:
      - /Current View1
    Name: Views
    Splitter Ratio: 0.5
  - Class: rviz/Time
    Experimental: false
    Name: Time
    SyncMode: 0
    SyncSource: ""
Visualization Manager:
  Class: ""
  Displays:
    - Alpha: 0.5
      Cell Size: 1
      Class: rviz/Grid
      Color: 160; 160; 164
      Enabled: true
      Line Style:
        Line Width: 0.03
        Value: Lines
      Name: Grid
      Normal Cell Count: 0
      Offset:
        X: 0
        Y: 0
        Z: 0
      Plane: XY
      Plane Cell Count: 10
      Reference Frame: Frame>
      Value: true
    - Class: rviz/TF
      Enabled: true
      Frame Timeout: 15
      Frames:
        All Enabled: true
        turtle1:
          Value: true
        turtle2:
          Value: true
        world:
          Value: true
      Marker Scale: 1
      Name: TF
      Show Arrows: true
      Show Axes: true
      Show Names: true
      Tree:
        {}
      Update Interval: 0
      Value: true
  Enabled: true
  Global Options:
    Background Color: 48; 48; 48
    Fixed Frame: world
    Frame Rate: 30
  Name: root
  Tools:
    - Class: rviz/Interact
      Hide Inactive Objects: true
    - Class: rviz/MoveCamera
    - Class: rviz/Select
    - Class: rviz/FocusCamera
    - Class: rviz/Measure
    - Class: rviz/SetInitialPose
      Topic: /initialpose
    - Class: rviz/SetGoal
      Topic: /move_base_simple/goal
    - Class: rviz/PublishPoint
      Single click: true
      Topic: /clicked_point
  Value: true
  Views:
    Current:
      Angle: -5.96046e-08
      Class: rviz/TopDownOrtho
      Enable Stereo Rendering:
        Stereo Eye Separation: 0.06
        Stereo Focal Distance: 1
        Swap Stereo Eyes: false
        Value: false
      Name: Current View
      Near Clip Distance: 0.01
      Scale: 48.8711
      Target Frame: Frame>
      Value: TopDownOrtho (rviz)
      X: -0.254099
      Y: -0.280596
    Saved: ~
Window Geometry:
  Displays:
    collapsed: false
  Height: 747
  Hide Left Dock: false
  Hide Right Dock: true
  QMainWindow State: 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
  Selection:
    collapsed: false
  Time:
    collapsed: false
  Tool Properties:
    collapsed: false
  Views:
    collapsed: true
  Width: 1364
  X: 0
  Y: 19

3. 详细分析

1.turtle_tf_broadcaster.cpp代码分析

（1）主函数中订阅turtle1/pose消息，当有消息时，调用消息响应函数poseCallback。

 ros::Subscriber sub = node.subscribe(turtle_name+"/pose", 10, &poseCallback);

（2）消息响应函数poseCallback调用sendTransform方法广播消息/tf消息
如下

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

2.rviz文件的结构

结构如图