When using manual data and non 'odom' world reference frame name, race condition results in incorrect transform.

[tgreier]

robot_localization/src/navsat_transform.cpp

Line 174 in ea976f9

datumCallback(request, response);

In our configuration, we use a manual datum and our world reference frame name is 'map' (not the default world_frame_id of 'odom'.
This results in an incorrect transform (cartesian -> world) being generated by navsat_transform.

This is a bit of a race condition because if our odometry callback is invoked before the transformCallback timer callback, then the world_frame_id is properly set, and the correct transform will be published.

[ayrton04]

Would it not make sense to have logic to force the transform computation to wait until the odometry callback has fired?

[tgreier]

@ayrton04 Yes, I thought about that. But that change seemed to be a fairly major alteration to how the manual datum is handled. I am happy to take a shot at changing the logic if you think that is the better solution.
I updated Pull Request #821 to wait for odom message before setting manual datum. Could you please review?