在ros下使用tf

tf真是一个好东西，把坐标变换都简化了

首先tf需要有一个broadcaster

#include <ros/ros.h>
#include <tf/transform_broadcaster.h>
#include <nav_msgs/Odometry.h>

void poseCallback(const nav_msgs::OdometryConstPtr& msg){
  static tf::TransformBroadcaster br;
  ROS_INFO("TF BROADCASTER");
  tf::Transform transform;
  transform.setOrigin( tf::Vector3(msg->pose.pose.position.x, msg->pose.pose.position.y, msg->pose.pose.position.z) );
  tf::Quaternion q;
  q.setRPY(0, 0, msg->pose.pose.orientation.z);
  transform.setRotation(q);
  //在这里确定了world frame
  br.sendTransform(tf::StampedTransform(transform, ros::Time::now(), "world", "pioneer_base"));
}

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

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

  ros::spin();
  return 0;
}

　　还要有一个listner

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

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

  ros::NodeHandle node;

  tf::TransformListener listener;

  ros::Rate rate(10.0);
  while (node.ok()){
    tf::StampedTransform transform;
    try{
      listener.lookupTransform("/pioneer_base", "/world",
                               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;
}

lookupTransform查找到的是target到source坐标变换

void Transformer::lookupTransform(
const std::string & target_frame,
const std::string & source_frame,
const ros::Time & time,
StampedTransform & transform
) const

http://docs.ros.org/kinetic/api/tf/html/c++/classtf_1_1Transformer.html#ac01a9f8709a828c427f1a5faa0ced42b

而tf_echo

http://wiki.ros.org/tf#tf_remap

格式是

tf_echo <source_frame> <target_frame>

是查找从source_frame 到 target_frame坐标系变换