Are localization warnings expected?

[bsb808]

When I run the VORC localization example from https://github.com/osrf/vorc/wiki/sensors

roslaunch vorc_gazebo marina.launch verbose:=true

and then

roslaunch vorc_gazebo localization_example.launch

I get the following transform warnings - perhaps a state publisher issue?

[ WARN] [1619375160.924654495, 648.733000000]: Transform from cora/imu_link to cora/base_link was unavailable for the time requested. Using latest instead.

[ WARN] [1619375161.138304949, 648.946000000]: Transform from cora/gps_link to cora/base_link was unavailable for the time requested. Using latest instead.

[ WARN] [1619375162.926686795, 650.733000000]: Transform from cora/imu_link to cora/base_link was unavailable for the time requested. Using latest instead.

[ WARN] [1619375163.239991691, 651.046000000]: Transform from cora/gps_link to cora/base_link was unavailable for the time requested. Using latest instead.

In the above, I'm using Melodic. There are other issues with Noetic - see bsb808/mrc_notes#4

[caguero]

I remember seeing these warnings since the beginning but never paid much attention to them. It looks like this is a discrepancy between the EKF update rate and the sensor update rate.

https://answers.ros.org/question/300345/robot-localization-package-transform-from-base_link-to-odom-was-unavailable-for-the-time-requested-using-latest-instead-imugps/

In the upper question, there's a reply with two potential workarounds:

You have two options:

a) Change your transform_time_offset EKF parameter to some small positive value. This will future-date its transform it's generating.

b) Set predict_to_current_time to true for the EKF. That will force the EKF to make a prediction to the current ROS time before publishing, rather than just publishing the state estimate at the time of the most recent measurement.