ROS 之工作空间

// tf_broadcaster.cpp
#include <ros/ros.h>
#include <tf/transform_broadcaster.h>

int main(int argc, char** argv){
  ros::init(argc, argv, "robot_tf_publisher");
  ros::NodeHandle n;

  ros::Rate r(100);

  tf::TransformBroadcaster broadcaster;
    //创建一个tf::TransformBroadcaster类的实例，用来广播 base_link → base_laser的变换关系

  while(n.ok()){
    broadcaster.sendTransform(
      tf::StampedTransform(
        tf::Transform(tf::Quaternion(0, 0, 0, 1), tf::Vector3(0.1, 0.0, 0.2)),
        ros::Time::now(),"base_link", "base_laser"));//Quaternion四元数来存储旋转变换的参数,第二个参数是坐标的位移变换,第三个参数是时间戳,第四个参数是母节点存储的参考系，即base_link，最后一个参数是子节点存储的参考系，即base_laser
    r.sleep();
  }
}

// tf_listener.cpp
#include <ros/ros.h>
#include <geometry_msgs/PointStamped.h>
#include <tf/transform_listener.h>//一个TransformListener对象自动订阅了ROS变换消息话题和管理所有的进入的转换数据

void transformPoint(const tf::TransformListener& listener){
  //创建一个函数，给定TransformListener，在“base_laser”坐标系中取一个点，并将其转换为“base_link”坐标系

  geometry_msgs::PointStamped laser_point;//创建一个点作为geometry_msgs::PointStamped,这里“Stamped”只是意味着它包含一个头，允许我们将时间戳和frame_id与消息相关联
  laser_point.header.frame_id = "base_laser";//因为我们在“base_laser”坐标系中创建一个点

  //we'll just use the most recent transform available for our simple example
  laser_point.header.stamp = ros::Time();

  //just an arbitrary point in space
  laser_point.point.x = 1.0;
  laser_point.point.y = 0.2;
  laser_point.point.z = 0.0;

  try{
    geometry_msgs::PointStamped base_point;
    listener.transformPoint("base_link", laser_point, base_point);//参数为我们想要将点转换为的坐标系的名称,我们正在转换的点,存储变换点
      //TransformListener对象d transformPoint()函数就是用来变换的

    ROS_INFO("base_laser: (%.2f, %.2f. %.2f) -----> base_link: (%.2f, %.2f, %.2f) at time %.2f",
        laser_point.point.x, laser_point.point.y, laser_point.point.z,
        base_point.point.x, base_point.point.y, base_point.point.z, base_point.header.stamp.toSec());
  }
  catch(tf::TransformException& ex){
    ROS_ERROR("Received an exception trying to transform a point from \"base_laser\" to \"base_link\": %s", ex.what());
  }//打印错误
}

int main(int argc, char** argv){
  ros::init(argc, argv, "robot_tf_listener");
  ros::NodeHandle n;

  tf::TransformListener listener(ros::Duration(10));

  //we'll transform a point once every second
  ros::Timer timer = n.createTimer(ros::Duration(1.0), boost::bind(&transformPoint, boost::ref(listener)));

  ros::spin();

}