I am using the artrackalvar package in Indigo to detect AR Tags and determine their respective poses. I am able to run the tracker successfully as I can visualize the markers in RViz. I give the following command to print the pose values

rostopic echo /arposemarker

and I get the following output indicating that the poses are determined.

header: 
  seq: 0
  stamp: 
    secs: 1444430928
    nsecs: 28760322
  frame_id: /head_camera
id: 3
confidence: 0
pose: 
  header: 
    seq: 0
    stamp: 
      secs: 0
      nsecs: 0
    frame_id: ''
  pose: 
    position: 
      x: 0.196624979223
      y: -0.238047436646
      z: 1.16247606451
    orientation: 
      x: 0.970435431848
      y: 0.00196992162831
      z: -0.126455066154
      w: -0.205573121457

Now I want to use these poses in another ROS node and hence I need to subscribe to the appropriate ROS message('arposemarker"). But I am unable to get enough information on the web on the header files and functions to use in order to extract data from the published message. It would be great if somebody can point to a reference implementation or documentation on handling these messages.