robot_localization and navsat_transform_node provide wrong pose

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Hi to all,

I'm trying to get a correct pose for my skid-steering vehicle by using IMU and RTK-GPS (from ublox).

I use navsat_transform_node to generate the /odometry/filtered by using /ublox_gps/fix combined with the /imu_data/ and then the ekf_localization_node as second instance.

The problem is that I'm not getting correct information under RVIZ. If I set odom frame as fixed frame in RVIZ, I can see nothing drawn by /odometry/filtered and /odometry/gps topics.

Should I have a map to make the robot_localization work? Do I need to publish a tf from map to odom frame?

The /odometry/filtered topic is generated by robot_localization, but I can't understand if it's correct and however I cannot plot it in RVIZ.

I cannot understand why I'm not able to see the path in RVIZ.

<launch>
    <node name="bl_gps" pkg="tf2_ros" type="static_transform_publisher" args="0 0 0 0 0 0 1 base_link gps" />
    <node name="bl_imu" pkg="tf2_ros" type="static_transform_publisher" args="0 0 0 0 0 0 1 base_link imu_link" />

 <node pkg="robot_localization" type="navsat_transform_node" name="navsat_transform_node" respawn="true" output="screen">
        <param name="magnetic_declination_radians" value="0"/>
        <param name="zero_altitude" value="false"/>
        <param name="publish_filtered_gps" value="false"/>
        <param name="broadcast_utm_transform" value="true"/>
        <param name="wait_for_datum" value="true"/>
        <rosparam param="datum">[18.33294909563789, 40.06012014572104, 0.0, odom, base_link]</rosparam>
        <remap from="/gps/fix" to="/ublox_gps/fix"/>
        <remap from="/odometry/filtered" to="/odometry/filtered"/>
        <remap from="/imu/data" to="/imu_data"/>
    </node>

    <node pkg="robot_localization" type="ekf_localization_node"  name="ekf_odom" clear_params="true">
        <param name="odom0" value="/odometry/gps"/>
        <param name="imu0" value="/imu_data"/>
        <param name="frequency" value="10"/>
        <param name="sensor_timeout" value="0.1"/>
        <param name="two_d_mode" value="false"/>
        <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,
                                        true,  true,  true,
                                        false, false, false,
                                        true,  true,  true,
                                        true,  true,  true]
        </rosparam>
        <param name="imu0_differential" value="false"/>
        <param name="imu0_remove_gravitational_acceleration" value="false"/>    
        <rosparam param="odom0_config">[true, true, true,
                                        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)/debug_ekf_localization.txt"/>    
    </node>

This is the output of /odometry/filtered:

    rostopic echo /odometry/filtered 
    header: 
      seq: 1286
      stamp: 
        secs: 1623059374
        nsecs: 659658909
      frame_id: "odom"
    child_frame_id: "base_link"
    pose: 
      pose: 
        position: 
          x: -325589.188922
          y: 2412419.0677
          z: 62.2733933113
        orientation: 
          x: 0.0109867434586
          y: 0.517231872535
          z: -0.0260019721528
          w: 0.855379669472
      covariance: [3.6044557794876098, -0.015878677513247248, 0.1368625236632224, 8.633587369403668e-11, -8.861249973655481e-10, -3.216145652088185e-11, -0.015878677513247248, 3.3048011011806797, -0.007119917916770026, 1.8472131111753644e-09, 6.326607301682415e-11, -8.108363233884301e-10, 0.13686252366322227, -0.00711991791677001, 2.268879609198499, -2.3844925176785617e-11, 1.621572947146949e-09, 1.6267748949876525e-16, 8.633587369403666e-11, 1.8472131111753646e-09, -2.3844925176785614e-11, 9.99667020457038e-07, 3.6771290652079676e-20, 2.2731193331381272e-15, -8.861249973655484e-10 ...