Question on frame transform

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Hi all,

After reading the tf tutorials, I think I'm almost understood the basics of ROS /tf. But when I did some test, I got a strange problem.

First, I created a frame called "turtleA" on (1, 1, 0) Also, I created a frame called "turtleB" on (10, 10, 0)

Then I wrote a simple listener1 to lookup turtleA to turtleB transform, and use getOrigin() to get position of turtle1 to turtle2. I ran my listener1. I expected to get (-9, -9). Right? But I got (-9, 9).

Is there anybody can help to check if anything I went wrong?

Here is the steps

A. Run turtlesim_node, create two more turtles

$ rosrun turtlesim turtlesim_node
$ rosservice call /spawn 1.0 1.0 0 turtleA
$ rosservice call /spawn 10.0 10.0 0 turtleB

(Here is the output log...)

[ INFO] [1434096863.907583199]: Starting turtlesim with node name /turtlesim
[ INFO] [1434096863.928566152]: Spawning turtle [turtle1] at x=[5.544445], y=[5.544445], theta=[0.000000]
[ INFO] [1434097013.827165207]: Spawning turtle [turtleA] at x=[1.000000], y=[1.000000], theta=[0.000000]
[ INFO] [1434097035.040781460]: Spawning turtle [turtleB] at x=[10.000000], y=[10.000000], theta=[0.000000]

B. Generate a frame called "turtleA" on (1, 1, 0)

// one one terminal
$ rosrun learning_tf turtle_tf_broadcaster __name:=turtleA turtleA

C. Generate a frame called "turtleB" on (10, 10, 0)

// on the other terminal
$ rosrun learning_tf turtle_tf_broadcaster __name:=turtleB turtleB

D. Here is my listener1 code.

int main(int argc, char** argv){
  ros::init(argc, argv, "my_tf_listener1");

  ros::NodeHandle node;


  tf::TransformListener listener;

  ros::Rate rate(10.0);
  while (node.ok()){
    tf::StampedTransform transform;
    try{
      listener.lookupTransform("/turtleB", "/turtleA",
                               ros::Time(0), transform);
    }
    catch (tf::TransformException &ex) {
      ROS_ERROR("%s",ex.what());
      ros::Duration(1.0).sleep();
      continue;
    }


    ROS_INFO("turtleA is on (%f, %f) to turtleB\n",
             transform.getOrigin().x(),
             transform.getOrigin().y());

    rate.sleep();
  }
  return 0;
};

E. My listener output

$ rosrun learning_tf turtle_tf_listener1 
[ERROR] [1434097444.841959496]: "turtleB" passed to lookupTransform argument target_frame does not exist. 
[ INFO] [1434097445.842391115]: turtleA is on (-9.000000, 9.000000) to turtleB
[ INFO] [1434097445.842532474]: turtleA is on (-9.000000, 9.000000) to turtleB
[ INFO] [1434097445.943704829]: turtleA is on (-9.000000, 9.000000) to turtleB

Plz help!! :)

Kevin Kuei