IMU and GPS fusion without odom - robot_localization

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I'm using ros Indigo, and trying to fuse IMU and GPS, I don't have any odom source. Reading forum and the roscon presentation about the robot_localization package, I tried the following configuration:

   <launch>
  <!-- gps and imu fusion -->
    <node pkg="robot_localization" type="navsat_transform_node" name="navsat_transform_node" respawn="true" output="screen">
    <param name="magnetic_declination_radians" value="0.36878808"/>
    <param name="zero_altitude" value="false"/>
    <param name="publish_filtered_gps" value="true"/>
    <param name="broadcast_utm_transform" value="true"/>
    <param name="wait_for_datum" value="true"/>

    <remap from="/gps/fix" to="/gps"/>
    <remap from="/imu/data" to="/imu"/>
    <remap from="/odometry/filtered" to="/odometry/map"/>
  </node>

 <!-- map frame -->
  <node pkg="robot_localization" type="ekf_localization_node"  name="map_transform" clear_params="true">

    <param name="odom0" value="odometry/gps"/>
    <param name="imu0" value="/imu"/>

    <param name="frequency" value="30"/>
    <param name="sensor_timeout" value="2"/>
    <param name="two_d_mode" value="true"/>

    <param name="map_frame" value="map"/>
    <param name="odom_frame" value="odom"/>
    <param name="base_link_frame" value="base_link"/>
    <param name="world_frame" value="map"/>

    <rosparam param="imu0_config">[false, false, false,
                                   false, false, true,
                                   false, false, false,
                                   false, false, true,
                                   true, false, false]</rosparam>

    <param name="imu0_differential" value="false"/>
    <param name="imu0_remove_gravitational_acceleration" value="true"/>

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

      <param name="odom0_differential" value="false"/>

    <param name="print_diagnostics" value="true"/>
    <param name="debug"           value="false"/>
    <param name="debug_out_file"  value="$(env HOME)/adroit_files/debug_ekf_localization.txt"/>

    <remap from="odometry/filtered" to="/odometry/map"/>

  </node>



<!-- odom frame -->
  <node pkg="robot_localization" type="ekf_localization_node"  name="odom_transform" clear_params="true">

    <param name="imu0" value="/imu"/>
    <param name="odom0" value="/odometry/map"/>

    <param name="frequency" value="30"/>
    <param name="sensor_timeout" value="2"/>
    <param name="two_d_mode" value="true"/>

    <param name="map_frame" value="map"/>
    <param name="odom_frame" value="odom"/>
    <param name="base_link_frame" value="base_link"/>
    <param name="world_frame" value="odom"/>

    <rosparam param="imu0_config">[false, false, false,
                                   false, false, true,
                                   false, false, false,
                                   false, false, true,
                                   true, false, false]</rosparam>

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

   <param name="odom0_differential" value="false"/>


    <param name="print_diagnostics" value="true"/>
    <param name="debug"           value="false"/>
    <param name="debug_out_file"  value="$(env HOME)/debug_ekf_localization.txt"/>

</node>

</launch>

as result, I'm getting a drift that increases in time, and the vector is always perpendicular to robot.

This warning appear several times too

[ WARN] [1465502165.359329185, 20.510000000]: Could not obtain base_link-> transform. Will not remove offset of navsat device from robot's origin.
[ WARN] [1465502167.550982133, 21.310000000]: Could not obtain transform from  to base_link. Error was Invalid argument passed to lookupTransform argument source_frame in tf2 frame_ids cannot be empty

I'm not using a real robot yet, for now I'm on gazebo, using hector_gazebo plugins for IMU and GPS.

IMU sample message:

  header: 
  seq: 10464
  stamp: 
    secs: 10
    nsecs: 918000000
  frame_id: base_link
orientation: 
  x: 0.019510418191
  y: -0.00138183083974
  z: -0.00971101353096
  w: 0.999761536739
orientation_covariance: [2.6030820491461885e-07, 0.0, 0.0, 0.0, 2.6030820491461885e-07, 0.0, 0.0, 0.0, 0.0]
angular_velocity: 
  x: -0.00310991562662
  y: -0.00912178750215
  z ...