Getting individual joint positions in openni_tracker

edit

Hi all,

I have openni_tracker running and publishing at /tf. I get following type of data if I try to publish /tf or save it in rosbag or text file.

transforms: 
  - 
    header: 
      seq: 0
      stamp: 
        secs: 1395050118
        nsecs: 781445267
      frame_id: /openni_depth_frame
    child_frame_id: /left_hand_1
    transform: 
      translation: 
        x: 2.29258546773
        y: 0.40955856152
        z: 0.746916322515
      rotation: 
        x: 0.499999999997
        y: 0.500001836603
        z: 0.499999999997
        w: 0.499998163397
---
transforms: 
  - 
    header: 
      seq: 0
      stamp: 
        secs: 1395050118
        nsecs: 781469499
      frame_id: /openni_depth_frame
    child_frame_id: /right_shoulder_1
    transform: 
      translation: 
        x: 2.45040462809
        y: -0.0277115992896
        z: 0.594173250142
      rotation: 
        x: 0.713314685492
        y: 0.667630701545
        z: 0.17342876346
        w: -0.123991410271
//--- and so on!

How can I subscribe to individual joints position, e.g. to only right_shoulder_1? I tried /tf/right_shoulder_1 but it didn't work. Shouldn't I be able to get even the translation of a joint? For example /tf/right_shoulder_1/translation/x should give me x translation position of right_shoulder_1.

The data saved together with all joints makes it difficult to use. I also need individual joint data in inside a program.

Thanks.