ROS 学习笔记（4）TF

Transform Configuration（变换配置）

两个坐标系：一个对应于机体中心点的坐标系（base_link），一个对应于扫描仪中心的坐标系（base_laser）。

tf假设所有的转换都是从parent到child的，我们选择“base_link”坐标系作为parent，其他的传感器等，都是作为“器件”被添加进robot的，转换关系的表达式应该是(x:0.1m,y0.0m,z:0.2m)。

$ cd %TOP_DIR_YOUR_CATKIN_WS%/src
$ catkin_create_pkg robot_setup_tf roscpp tf geometry_msgs
$ vi robot_setup_tf/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;

    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"
            )
        );
        r.sleep();
    }
}

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

void transformPoint(const tf::TransformListener& listener){
  //we'll create a point in the base_laser frame that we'd like to transform to the base_link frame
  geometry_msgs::PointStamped laser_point;
  laser_point.header.frame_id = "base_laser";

  //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);

    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());
  }
}

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();
}

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

$ cd %TOP_DIR_YOUR_CATKIN_WS%
$ catkin_make

好的，万事俱备只欠东风！让我恩试着实际运行下吧。这部分，你需要开三个终端窗口

第一个窗口，运行core

roscore

第二个，运行 tf_broadcaster

rosrun robot_setup_tf tf_broadcaster

好的。现在，我们会在第三个窗口运行tf_listener，将从传感器坐标系获取的虚拟点，变换到机体坐标系。

rosrun robot_setup_tf tf_listener

抄自：http://wiki.ros.org/cn/navigation/Tutorials/RobotSetup/TF