Help with robot_localization warnings: "Transform from A to odom was unavailable for the time requested. Using latest instead."

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Hello all,

I have been trying to troubleshoot this for a while, but haven't gotten far with it.

The SETUP:

I am trying to fuse pose with odometry data from two cameras zed and realsense (rs). The pose comes from zed in map frame (zed_map) and the odom from realsense in odom frame (camera_odom_frame). Both have their own tf trees as both run their own estimation algorithms. The final output TF tree is present in the attachment: frames

In order to link the rs camera_odom_frame to the robot base_link, I have written a custom tf broadcaster. Basically I know the tf between the base_link --> camera_link and the rs generates camera_link --> camera_odom_frame. Using this information I am able to derive the tf base_link --> camera_link. Below is the code that I use to broadcast the new generated tf. A very identical node is written to generate base_link --> zed_map tf.

int main(int argc, char** argv){
    ros::init(argc, argv, "rs_tf_broadcaster");
    ros::NodeHandle node;

    tf::TransformListener listener;

    ros::Rate rate(200.0);
    while (node.ok()){

        tf::StampedTransform lu_tf;
        try{
            listener.waitForTransform("camera_link", "camera_odom_frame",ros::Time::now(), ros::Duration(4.0));
            listener.lookupTransform("camera_link","camera_odom_frame",
                                    ros::Time(0), lu_tf);
        }

        catch (tf::TransformException ex){
            ROS_ERROR("%s",ex.what());
            //ros::Duration(1.0).sleep();
        }
        tf::Transform base_to_rsbase_tf;
        tf::Quaternion q_rs;
        q_rs.setRPY(0, 0.83, 0);
        tf::Vector3 vec3_rs(0.265, 0.12, 1.0);

        base_to_rsbase_tf.setOrigin(vec3_rs);
        base_to_rsbase_tf.setRotation(q_rs);

        tf::Transform rsbase_to_rsodom_tf;
        rsbase_to_rsodom_tf.setOrigin(lu_tf.getOrigin());
        rsbase_to_rsodom_tf.setBasis(lu_tf.getBasis());

        tf::Transform base_to_rsodom_tf;
        base_to_rsodom_tf = base_to_rsbase_tf * rsbase_to_rsodom_tf; //VERIFIED

        static tf::TransformBroadcaster br_rs;
        br_rs.sendTransform(tf::StampedTransform(base_to_rsodom_tf, ros::Time::now(), "base_link", "camera_odom_frame"));

        rate.sleep();
    }
  return 0;
};

The launch file used to launch robot_loclaization is simple:

<launch>

<node pkg="robot_localization" type="ekf_localization_node" name="ekf_localization">
<rosparam command="load" file="$(find cognimo)/config/ekf_localization.yaml"/>
</node>

</launch>

The yaml file for localization is linked here.

Now I come to the ISSUE at hand: I am able to run the robot_localization node i.e. ekf_localization. Upon running I get the following error message and the repeated warnings:

[ WARN] [1598303517.049491085]: Could not obtain transform from camera_pose_frame to base_link. Error was Lookup would require extrapolation into the past.  Requested time 1598303517.048263512 but the earliest data is at time 1598303517.052134514, when looking up transform from frame [camera_pose_frame] to frame [base_link]

[ WARN] [1598303517.054181358]: Transform from camera_pose_frame to base_link was unavailable for the time requested. Using latest instead.

[ WARN] [1598303519.076994401]: Transform from camera_pose_frame to base_link was unavailable for the time requested. Using latest instead.

[ WARN] [1598303521.077250369]: Transform from camera_pose_frame to base_link was unavailable for the time requested. Using latest instead.

[ WARN] [1598303523.097323886]: Transform from camera_pose_frame to base_link was unavailable for the time requested. Using latest instead.

[ WARN] [1598303525.123948904]: Transform from zed_map to odom was unavailable for the time requested. Using latest instead.

[ WARN] [1598303527.161387025]: Transform from camera_pose_frame to base_link was unavailable for the time requested. Using latest instead.

[ WARN] [1598303529.191298926]: Transform from zed_map to odom ...