Navsat_transform_node does not subscribe to IMU topic

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Hello,

I am currently trying to use the navsat_transform_node from the robot_localization package in a ROS-Gazebo simulation. I'm using Ubuntu 16.04 LTS, with ROS kinetic and Gazebo 7.

In order to work, this node needs to subscribe to 3 differents topics : an odometry topic with nav_msgs/Odometry message, an IMU topic with sensor_msgs/Imu and a GPS topic with sensor_msgs/NavSatFix.

My problem is that, when launching the navsat_transform_node does not subscribe to my IMU topic, even if the message type of the IMU topic published by gazebo is sensor_msgs/Imu. However, the node does subscribe to the odom and gps topics.

Here is my launch file (taken from the robot localization wiki) :

<?xml version="1.0" encoding="UTF-8"?>
<launch>
  <node pkg="robot_localization" type="navsat_transform_node" name="navsat_transform_node" respawn="true">
    <param name="magnetic_declination_radians" value="0"/>
    <param name="yaw_offset" value="0"/>
    <remap from="/imu/data" to="/imu_data" />
    <remap from="/gps/fix" to="/gps/fix" />
    <remap from="/odometry/filtered" to="/odom" />
  </node>
</launch>

Here is the IMU code from the URDF file of my robot model :

  <joint name="imu_joint" type="fixed">
    <axis xyz="0 0 1"/> <!-- 0 1 0 -->
    <origin xyz="${length_chassis*(5/16)} 0 ${height_chassis-(wheel_radius/2)}"/>
    <parent link="base_link"/>
    <child link="imu_link"/>
  </joint>

<link name="imu_link">
  <inertial>
    <mass value="0.001"/>
    <origin rpy="0 0 0" xyz="0 0 0"/>
    <inertia ixx="0.0001" ixy="0" ixz="0" iyy="0.000001" iyz="0" izz="0.0001"/>
  </inertial>
  <visual>
    <origin rpy="0 0 0" xyz="0 0 0"/>
    <geometry>
      <box size=" ${IMU_size} ${IMU_size} ${IMU_size}"/>
    </geometry>
    <material name="green"/>
  </visual>
  <collision>
    <origin rpy="0 0 0" xyz="0 0 0"/>
    <geometry>
      <box size="${IMU_size} ${IMU_size} ${IMU_size}"/>
    </geometry>
  </collision>
</link>

And here is the IMU plugin :

<gazebo >
    <plugin name="imu_plugin" filename="libhector_gazebo_ros_imu.so">
      <alwaysOn>true</alwaysOn>
      <bodyName>imu_link</bodyName>
      <frameId>imu_link</frameId>
      <topicName>/imu_data</topicName>
      <serviceName>imu_service</serviceName>
      <gaussianNoise>0.0</gaussianNoise>
      <updateRate>20.0</updateRate>
      <xyzOffsets>0 0 0</xyzOffsets>
      <rpyOffsets>0 0 0</rpyOffsets>
    </plugin>    
</gazebo>

When echo-ing the topic /imu_data, I get :

---
header: 
  seq: 327
  stamp: 
    secs: 16
    nsecs: 400000000
  frame_id: "imu_link"
orientation: 
  x: 4.69962116857e-06
  y: -4.8838604247e-08
  z: 7.97720664175e-05
  w: 0.999999996807
orientation_covariance: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
angular_velocity: 
  x: -4.49165569326e-13
  y: 6.43295283435e-15
  z: 2.52244385042e-12
angular_velocity_covariance: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
linear_acceleration: 
  x: 3.40118210419e-07
  y: 9.18946096526e-05
  z: 9.79999999084
linear_acceleration_covariance: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
---

Also, @Tom Moore told me to post a sample message for every sensor input, so here is the sample from the topic /odom :

---
header: 
  seq: 165673
  stamp: 
    secs: 1661
    nsecs: 260000000
  frame_id: "odom"
child_frame_id: "base_link"
pose: 
  pose: 
    position: 
      x: 0.267229286097
      y: 0.00580914153162
      z: 0.299999489939
    orientation: 
      x: 1.20893461539e-05
      y: -8.60155713043e-08
      z: 0.0124744407312
      w: 0.999922191064
  covariance: [1e-05, 0.0, 0.0, 0 ...