PX4 topics can't be plotted

[dakejahl]

Hello, thanks for the project! I've been using it with PX4 for a year or two now and it's been invaluable.

I am trying to use PlotJuggler to subscribe to an /fmu topic over the DDS bridge from a device connected on the same network, but the topic doesn't appear in the list in PJ. All of the other topics from running nodes do appear, just not the /fmu topics. Strangely if I run ros2 topic hz /fmu/out/vehicle_attitude on the device the topic appears in the list, but PJ still fails to plot it. I suspect this might be related to the QoS settings but I'm not sure.
https://docs.px4.io/main/en/middleware/uxrce_dds.html#px4-ros-2-qos-settings

PX4 uses the following QoS settings for publishers:

uxrQoS_t qos = {
  .durability = UXR_DURABILITY_TRANSIENT_LOCAL,
  .reliability = UXR_RELIABILITY_BEST_EFFORT,
  .history = UXR_HISTORY_KEEP_LAST,
  .depth = 0,
};

I added some debug printout in DataStreamROS2::subscribeToTopic and I see the QoS settings don't match the above (/camera/imu is from a realsense node and I am able to plot, it likely has default QoS settings)

subscribeToTopic:  /camera/imu
durability:  2
reliability:  1
history:  1
depth:  10

subscribeToTopic:  /fmu/out/vehicle_attitude
durability:  2
reliability:  1
history:  1
depth:  10

[rosiakpiotr]

Probably stale but for newcomers, related and closed issue: PlotJuggler/PlotJuggler#583
Long story short, chances are apt version of plotjuggler-ros for your system is older than the one containing fix.
Can be verified with

apt show ros-${ROS_DISTRO}-plotjuggler-ros

[facontidavide]

So, unless your client PC has the custom message sourced / installed (in this case px4_msgs), PlotJuggler will be unable to understand it.

Of cours it may also be a QoS problem. To better diagnose this issue, try if ros2 topic echo .. works or not.