ekf_localization with gps and imu

edit

I looked at the data from your other post, and this is what navsat_transform_node is outputting:

You can get this plot by doing:

rostopic echo -p /odometry/gps > odom_gps.txt

...and then plotting the output with MATLAB.

This says to me that navsat_transform_node is behaving correctly, but keep reading.

Without doing a deeper analysis, my first guess is that your IMU may not be mounted correctly. If, for example, you have it turned around and facing the wrong direction, then navsat_transform_node will be outputting incorrect positions if you don't correct for the offset, and ekf_localization_node will think your robot is facing the wrong way, so when the EKF makes a prediction, it will move your robot the wrong way.

Please do this: do not remove any information from your question. Instead, at the bottom, add an "EDIT" section, and post a photo, if possible, of the IMU on your robot, and please make it clear where the front of your robot is. Also, although I believe I am aware of it, let me know if you're using this fork of the GX2 node, or the default one, as it will affect my answer.

EDIT 1:

Here's what I did:

1. Downloaded your miercoles.bag file

2. Ran this command (to get rid of the topics I didn't want):

   rosbag filter miercoles.bag gps_test.bag "topic != '/diagnostics' and topic != '/odometry/filtered' and topic != '/rosout' and topic != '/rosout_agg' and topic != '/tf' and topic != '/odometry/gps'"
   

3. Downloaded the latest source for robot_localization, and used the indigo-devel branch
4. Created this launch file:

<launch>

<param name="/use_sim_time" value="true" />

<node pkg="tf" type="static_transform_publisher" name="bl_imu" args="0 0 0 0 0 0 1 /base_link /imu 20" />
<node pkg="rosbag" type="play" name="player" output="screen" args="--clock /home/tmoore/Desktop/gps_test.bag -d 3"/>

<node pkg="robot_localization" type="ekf_localization_node" name="ekf_localization" clear_params="true">
  <param name="frequency" value="30"/>  
  <param name="sensor_timeout" value="0.1"/>  
  <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"/>

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


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

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

  <param name="odom0_differential" value="false"/>
  <param name="imu0_differential" value="false"/>

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

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

  <!-- ======== ADVANCED PARAMETERS ======== -->

  <param name="odom0_queue_size" value="2"/>
  <param name="imu0_queue_size" value="10"/>

  <param name="debug"           value="false"/>
  <param name="debug_out_file"  value="/home/tmoore/Desktop/debug_ekf_localization.txt"/>

  <rosparam param="process_noise_covariance">[0.05, 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, 0.05, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0 ...