Plans to make realsense-ros node a lifecycle node? [ROS2]

[anaelle-sw]

Hello,

in our use case, we regularly plug / un-plug cameras (D435) to our system. We need to adapt the number of realsense-ros nodes running according to the current number of embedded cameras, at runtime without re-launching our whole ROS application.

Previously, with ROS1, we used to simply kill / launch the realsense-ros nodes with system calls.

ROS2 offers the possibility to use LifecycleNodes (ROS2 design documentation here and a demo here). We would be super interested in using realsense-ros nodes as lifecycle nodes, especially for two reasons:

• easily activate / deactivate the realsense-ros nodes at runtime (while our system is in some kind of a sleep mode)
• easily configure / unconfigure a realsense-ros node at runtime (depending of the number of cameras being added / removed to our system)

(By "activate / deactivate / configure / unconfigure" I am directly referring to the lifecycle node's states transitions (see doc link above), and by "easily", I mean that these transitions can be triggered by an external node of our own, which would be able to ask the lifecycle realsense-ros node to change from a state to another)

Well my question is: are you considering to make realsense-ros a ROS2 lifecycle node? If so, any idea of the time it will take until it would be implemented?
If this is not part of your plans for now, would you still accept a pull request to implement this? Even if, obviously, there would be a lot of discussions to have about the design of it, before implementing anything.
I am just asking to know if lifecycle nodes are something you could consider at some point, or if there is just no room for lifecycle nodes in realsense-ros development.

Thank you!

[MartyG-RealSense]

Hi @anaelle-sw Thanks very much for your question! Support for lifecycle nodes in the RealSense ROS2 wrapper is a feature that has previously been suggested by a RealSense ROS community member in the link below.

realsenseai/librealsense#5825 (comment)

In regard to whether lifecycle node support is part of official future plans for the RO2 wrapper or whether a PR would be the preferable option, I will refer that question to @doronhi the RealSense ROS wrapper developer.

[doronhi]

Hi @anaelle-sw
Making realsense2_camera a lifecycle node is indeed in our intentions. It is currently planned for the last quarter of 2021 but currently not prioritized very high. Your indication that this feature is useful may boost it up.
As you say, it requires a design change. Any discussion and requirements description is very much appreciated.

[anaelle-sw]

Hi, thanks to both of you for your answers!

Any discussion and requirements description is very much appreciated.

Well for the moment, the three main features that we would appreciate with lifecycle nodes are:

• Launching a realsense-ros node (but not configuring it, just keeping it un-configured). Then, when we connect a camera at runtime, configuring the realsense-ros node for this new camera
• Un-configuring a realsense-ros node at runtime (but not killing it, just keeping it un-configured) when we disconnected the associated camera
• Activating / de-activating a realsense-ros node to start / stop all streams (it could be quite equivalent to the "/enable" service already existing)

[doronhi]

Hi,
Thank you for your comments and requirement description.
In the current version, if you start the node with the camera detached, the node just hangs there. When the camera is attached it is automatically detected, configured, and started. When the camera disconnects the node stays there, waiting for the camera to reconnect. Is that the behavior you wish to keep under the life-cycle structure?

[anaelle-sw]

Hello,

Is that the behavior you wish to keep under the life-cycle structure?

Well, almost yes, but at with two main differences I think:

• If the node is started, some error/warning messages will be output if the camera is not connected. But in our use case, it is not a "problem" if some cameras are not connected. Actually, to be a bit more precise, the number of cameras is just a part of different possible configurations of our system. So a lot of time can pass without any new camera being connected. In this case, it would be better to have the realsense node in some kind of a sleep mode (as in the Lifecycle state "unconfigured").
• When a camera is disconnected, we would need the realsense-ros node be unconfigured, and not "waiting for the camera to reconnect", as you said. Actually, even if two configurations have the same number of cameras, the position of these cameras may change, for instance. So more than just waiting the camera to reconnect, we need to setup the realsense node's parameters every time a camera is newly connected / re-connected. Because if the configuration has changed, some important parameters may have changed in the mean time

Hope this can help, let me know if you need more details. Thanks for support!

[doronhi]

As said, there is still some time before work will begin. For now, I internally logged your remarks under DSO-17089.
Thanks for the input.

[MartyG-RealSense]

Hi @anaelle-sw As lifecycle node plans for the ROS wrapper are set for some time in the future and your feedback has been logged by @doronhi - is it okay to close this case please? Thanks!

[anaelle-sw]

Hello, yes sure, thanks for support

[MartyG-RealSense]

You are very welcome @anaelle-sw - thanks very much for the update!

[doisyg]

Hello,
Any update on this issue ? Is it still planned for the end of the year ?

[imstevenpmwyca]

Hello @doronhi,
Is there any update regarding this lifecycle functionality? Would you share with us its current state or road-plan?
Thank you very much and kind regards!

[SamerKhshiboun]

Hi @anaelle-sw, @imstevenpmwyca,
My name is Samer, and I am a developer in the RealSense SW Team.
As I got to this very interesting issue, I started to investigate the Lifecycle concept in ROS2 and estimating the effort we need to do these changes.
I will update asap.
Thank you.

[alonsnir]

Any progress on this one?