ROS Time API and Simulation Time

[josephcoombe]

The hebiros_node and hebiros_gazebo_plugin codes should support the following interaction between the ROS Time API and Simulation Time.

In order for a ROS node to use simulation time according to the /clock topic, the /use_sim_time parameter must be set to true before the node is initialized. This can be done in a launchfile or from the command line.

It's worth mentioning that while "roslaunch does not guarantee any particular order to the startup of nodes", parameters set in a .launch file "will be stored on the Parameter Server before any nodes are launched."

If the /use_sim_time parameter is set, the ROS Time API will return time=0 until it has received a value from the /clock topic. Then, the time will only be updated on receipt of a message from the /clock topic, and will stay constant between updates.

For calculations of time durations when using simulation time, clients should always wait until the first non-zero time value has been received before starting, because the first simulation time value from /clock topic may be a high value.

(from http://wiki.ros.org/Clock#Using_Simulation_Time_from_the_.2BAC8-clock_Topic)

[josephcoombe]

#103 is an example of where mishandling this can bite you.

[josephcoombe]

Perhaps pertinent: http://answers.gazebosim.org/question/20646/libgazebo_ros_diff_drive-publishes-tf-based-on-wall-clock-time-instead-of-sim-time/

Issue with (some) Gazebo Plugins using wall clock time instead of simulation time due to a change in rostime dating from May 18th 2018 and released on September 6th, 2018.

[josephcoombe]

@iamtesch this may be helpful regarding ROS Time and Gazebo simulation

[MahaprabuLogicalmindsit]

i want to calculate the estimation time for my goal how to do that