navsat_transform_node has zero orientation output?

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I'm working with a robot with no wheel odometry measures, and have IMU, GPS and motor commands to fuse. Can anyone clarify how the setup should work for this?

At the moment I have GPS, IMU and motor command odometry going into a navsat_transform_node, which outputs odometry messages. I'm planning to fuse them with a second copy of the motor commands with an ekf_localization node.

My problem is: the odometry/gps messages coming out of the navsat_transform_node all contain zeros for all orientations. I thought the IMU data was being used to set these (and I've check the incoming IMU messages are non-zero).

Am I doing something wrong, or mis-interpreting what navsat_transform_node is doing? Perhaps the IMU is used like the motor command odometry to set only the initial state, then ignored the rest of the time? Even with that, it would be unlikely to have orientation exactly 0 at the start. Do I still need to fuse the odometry/gps with IMU again to get the desired effect, and if so why?

Thanks for any insights!

Sample odometry/gps message below:

position:

  x: 0.806593844667
  y: -4.15517381765
  z: -0.674990490428
orientation: 
  x: 0.0
  y: 0.0
  z: 0.0
  w: 1.0

covariance: [1.259293318748, 0.03294127204511593, 0.41883145581259457, 0.0, 0.0, 0.0, 0.03294127204511593, 1.232013681194764, 0.2798927172566257, 0.0, 0.0, 0.0, 0.41883145581259457, 0.2798927172566257, 4.768693000057238, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0] twist: twist: linear: x: 0.0 y: 0.0 z: 0.0 angular: x: 0.0 y: 0.0 z: 0.0 covariance: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]