robot_localization failed to transform warning

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I pulled down your launch and bag file while I had DropBox access the other day, and am just now looking at them. Here are the problems I see. Note that I don't think I have your latest launch file, as the topic names appear to be very different.

1. Here is a sample IMU message from the bag file:

   header: 
     seq: 756
     stamp: 
       secs: 1439616291
       nsecs: 130379310
     frame_id: Imu_link
   orientation: 
     x: 1.0
     y: 0.0
     z: 0.0
     w: 0.0
   orientation_covariance: [0.01, 0.0, 0.0, 0.0, 0.01, 0.0, 0.0, 0.0, 100.0]
   angular_velocity: 
     x: 0.0
     y: 0.0
     z: -0.05
   angular_velocity_covariance: [1e-06, 0.0, 0.0, 0.0, 1e-06, 0.0, 0.0, 0.0, 1e-06]
   linear_acceleration: 
     x: 0.0
     y: 0.0
     z: 0.0
   linear_acceleration_covariance: [0.02, 0.0, 0.0, 0.0, 0.02, 0.0, 0.0, 0.0, 0.02]
   

   First, the orientation appears to be the identity quaternion, but the identity quaternion should have x = 0.0 and w = 1.0. Second, if your IMU doesn't report orientation, navsat_transform_node will not function. See "Required Inputs" here. You'll need an earth-referenced heading, e.g., from a compass.

2. The launch file I'm looking at doesn't appear to show anything to do with the navsat_transform_node, but just looking at the error message above, I think you must have your GPS odometry configuration something like this:

    <rosparam param="odom0_config">[false, false, false, 
                                    false, false, false, 
                                    true,  false, false, 
                                    false, false, false, 
                                    false, false, false]</rosparam>
   

   First, make sure that your odom0 setting really is for the GPS odometry. Next, note that the GPS odometry data only has pose information (X, Y, and optionally Z) in it. The configuration settings above are incorrect, because they have X velocity set to true. In your case, the reason I think you have something akin to the configuration above is that the transform failure was from an empty frame_id to base_footprint. The only time the filter attempts to transform into the body frame is when it's attempting to fuse a velocity. Your GPS odometry message has a blank child_frame_id (for the velocity component of the message), and the filter is trying to transform it into the body frame.

In any case, you should first fix your IMU message, and we'll go from there.

EDIT in response to the comments below

We'll pretend for a moment that you have a compass in your IMU so that I can address your question.

The use_odometry_yaw parameter, when set to true, renders the IMU input to navsat_transform_node unnecessary, yes. However, if you were to turn on differential mode or relative mode for your yaw sensor within ekf_localization_node, then you wouldn't be able to use the use_odometry_yaw setting, and you'd have to use your IMU directly with navsat_transform_node. This is because the yaw that you feed to navsat_transform_node must be earth-referenced. In other words, if you ... (more)