AirSim (+ ROS wrapper) not publishing clock when /use_sim_time is set to true?

[zdjeffri]

Bug report

• AirSim Version/#commit: commit 8057725712c0cd46979135396381784075ffc0f3
• UE/Unity version: 4.27.2-18319896
• autopilot version: N/A
• OS Version: Windows 11 21H2, Ubuntu 20.04.4, ROS Noetic, (Using WSL2)

What's the issue you encountered?

Using AirSim to simulate lidar data for an autonomous robot. Have the clock speed for AirSim set at 0.5 (via settings.json). Can confirm this works properly because the clock topic is running at half-speed when the "use_sim_time" rosparam is false. However, if "use_sim_time" is set to true, the clock is no longer published and the ROS Wrapper ceases to publish anything. In order to properly integrate the AirSim clock with other ROS nodes, "use_sim_time" needs to be set to true so that the ROS Time API returns what is being published by AirSim instead of the system clock.

Settings and other relevant files

AirSim Settings - settings.json roslaunch file - airsim_node.launch

How can the issue be reproduced?

1. Apply the settings.json
   • the only pertinent settings are the host and clock speed. the vehicle doesn't matter.
2. Adjust the launch file
   • publish_clock is set to true
     • because it is a private nodehandle publisher, I also remap is from /airsim_node/clock to /clock. This isn't pertinent to the issue though.
   • use_sim_time is set to true
     • required so that other ros nodes run on same clock as AirSim
3. Launch the file: roslaunch airsim_ros_pkgs airsim_node.launch output:=screen host:=$WSL_HOST_IP
4. press play in AirSim in separate unreal window, wait for the AirSim ros node to connect
5. rostopic echo any of the AirSim topics - nothing is being published

[zdjeffri]

I'll add, that in ROS terms at least, the airsim_node is not acting as a clock server when "use_sim_time" is true, but when "use_sim_time" is false, it is acting as a clock server. It should work in both cases, given "publish_clock" is set to true in the launchfile. Hopefully, this clarifies the issue.

[yhabib29]

Hello, I also had an issue using ROS wrapper regarding simulated clock. I was recording all data into a rosbag. To be able to record simulated data and clock while using a custom ClockSpeed I did the following:

1. Renamed clock topic from /airsim_node/clock to /clock. To do this, I replaced NodeHandle nh_private_ to nh_ in airsim_ros_wrapper.cpp:319 :

clock_pub_ = nh_.advertise<rosgraph_msgs::Clock>("/clock", 1);

Do not forget to build the plugin after doing this modification.

2. Launch airsim_node using following command:

roslaunch airsim_ros_pkgs airsim_node.launch publish_clock:=true

3. Record topic in a bag after setting /use_sim_time param to true in the same terminal:

rosparam set use_sim_time true
rosbag record /airsim_node/Drone1/front_left_custom/Scene /tf /tf_static -O airsim.bag

This way, my rosbag is recorded using published clock.

When I play the rosbag file without any specific option everything works well

rosbag play airsim.bag

You can also check your bag file using:

rosbag info --freq airsim.bag

[zdjeffri]

@yhabib29 What version of AirSim are you using? Are you using a car or a drone? What version of ROS? This solution did not work. AirSim, whether using public or private nodehandle, only publishes clock if use_sim_time is false - which is my problem. If use_sim_time is true, clock is not published.

[yhabib29]

Hey @zdjeffri , sorry again, I have just checked the whole pipeline and I was wrong in my second comment (removed). I edited my first comment again with the correct procedure ! Let me know if it works for you.

[zdjeffri]

Any updates to airsim_ros that addresses this issue? the above method works for recording bag files but does not enable testing navigation algorithms in simulation (i.e. SIL). Can force ROS to use real-time but then if Airsim clock speed is != 1.0, there are timing issues.

[dylanyd]

I recently meet the same problem and solve it by changing the timer of drone_state_timer_cb from ros::Timer to ros::WallTimer.

[andrewjong]

The issue seems to be that AirSim's ROS wrapper publishes /airsim_node/clock based on ros::Timer, which when use_sim_time=true only runs if /clock is advancing. So it's a chicken-egg problem.

// airsim_ros_wrapper.h
    ros::Timer airsim_control_update_timer_;

// airsim_ros_wrapper.cpp
    airsim_control_update_timer_ = nh_private_.createTimer(
            ros::Duration(update_airsim_control_every_n_sec), 
            &AirsimROSWrapper::drone_state_timer_cb, this);

void AirsimROSWrapper::drone_state_timer_cb(const ros::WallTimerEvent& event)
{
    // other stuff
        // publish the simulation clock
        if (publish_clock_) {
            clock_pub_.publish(ros_clock_);
        }
   // other stuff
}

@dylanyd's ros::WallTimer solution is a valid workaround that makes airsim_control_update_timer_ advance from the system clock instead of ROS' /clock topic. However a fully correct solution would be to somehow sync to AirSim/Unreal Engine's internal clock. That way setting AirSim's clockspeed will also synchronize here. Not sure how to do that yet. Will update when that's figured out.