Access tf Vector3 values

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Hello,

I would like to get the z position value of my robot in gazebo. My Robot is using a skid steering plugin publishing on the "/player0/odom" topic and the "/tf" topic with "player0/frame" as it's frame id.

I do know how to get the x and y values by using the odom topic, but to get the z value it seems I have to use tf. However, the tf data confuses me.

If I echo the /tf topic, I get:

transforms:

header: 
  seq: 0
  stamp: 
    secs: 8
    nsecs: 402000000
  frame_id: player0/frame
child_frame_id: root
transform: 
  translation: 
    x: -2.00000384203
    y: -0.000426774126042
    z: 0.400000377264
  rotation: 
    x: -4.57302626635e-07
    y: 9.54536038539e-08
    z: -0.00161574482528
    w: 0.999998694683

How can I get the z: 0.4...value and store it into a variable?