Re-enable grab_compute_capping_fps to Reduce Processing Load / Power Consumption

[nseyffer]

Preliminary Checks

• This issue is not a duplicate. Before opening a new issue, please search existing issues.
• This issue is not a question, bug report, or anything other than a feature request directly related to this project.

Proposal

In the ROS2 wrapper 5.0 (Jazzy) with ZED SDK 5.0, setting low frame-rates via the general.pub_frame_rate and related parameters reduced the internal processing frequency.

In the current ros2 wrapper (tested on jazzy_5.1 or master branch) with ZED SDK 5.1, this behavior changed. The wrapper now explicitly sets: mInitParams.grab_compute_capping_fps = 0.0f;

I found that restoring the original behavior: mInitParams.grab_compute_capping_fps = static_cast<float>(mVdPubRate); again makes frame-rate settings directly influence the processing load significantly.

I would very much appreciate it, if this feature will be brought back in the future.

Use-Case

For many robotics applications, especially mobile robots or battery-powered platforms, it is highly beneficial to reduce compute load when high-frequency depth/object processing is unnecessary.
Being able to cap the grab/compute rate allows lower power consumption, reduced heat generation, increased battery runtime, lighter GPU/CPU load when operating in low-demand modes.

This was previously possible in zed-ros2-wrapper 5.0 but is no longer available.

Anything else?

Maybe an additional config parameter for this, such as general.grab_compute_capping_fps would be beneficial.
Thank you!

[Myzhar]

Hi @nseyffer
to reduce the processing load, you can:

• change the grab frequency to a lower value
• change the publishing frequency for the video/depth topic and/or point cloud

This new behavior is more flexible because the grab_compute_capping_fps parameter was affecting all the modules at the same way.

[nseyffer]

Hi @Myzhar,

thank you for your reply.
I tried both approaches without success. When trying to set the parameter general.grab_frame_rate to 10 fps (matching my current setting of pub_frame_rate and point_cloud_freq), I get:

[component_container_isolated-2] [WARN] [1764944789.350757760] [zed2i_front.zed_node_front]: !!! general.grab_frame_rate value is not valid: '10'. Automatically replaced with '15'. Please fix the parameter !!!

I assumed, this is because the possible frame rates are limited to 15, 30, 60 fps (at 720p), as listed here: https://www.stereolabs.com/docs/video/camera-controls#frame-rate

The change of depth.point_cloud_freq and general.pub_frame_rate (e.g., from 10 fps to 1 fps) does change the publishing frequencies, but internal processing seems to remain unchanged, since the system's power draw does not change, unless the mInitParams.grab_compute_capping_fps code line is activated.

[Myzhar]

I assumed, this is because the possible frame rates are limited to 15, 30, 60 fps (at 720p), as listed here: https://www.stereolabs.com/docs/video/camera-controls#frame-rate

Yes, you must use the supported grab rates. The minimum value is 15 FPS.

depth.point_cloud_freq and general.pub_frame_rate only affect the behaviours of the ZED ROS2 Wrapper; they do not change how the ZED SDK works.
If you set them to 1 FPS, but the topics are not subscribed to, you will not notice any difference regarding the system load.
They've been introduced just to reduce the load required by the DDS communication.

[nseyffer]

Thanks for the clarification!
So with the current design there is no way to reduce the internal processing rate below the minimum grab rate of 15 fps, unless the grab_compute_capping_fps line is restored. That matches what I observed during testing.
I understand the goal of the new, more flexible behaviour. My suggestion for an optional parameter (e.g., general.grab_compute_capping_fps) was simply to give users the choice to lower the SDK’s internal compute load below 15 fps.

If this isn’t something planned on your roadmap, I understand. In that case, feel free to close the issue or let me know and I can close it.
Thanks again for the quick responses and the great work on the wrapper!

[Myzhar]

Do not close it. We can consider a mix of features of this type for the next release of the wrapper.
Meanwhile, you can add it yourself by modifying the code to verify that it works as expected:

zed-ros2-wrapper/zed_components/src/zed_camera/src/zed_camera_component_main.cpp

Line 2506 in 458c725

mInitParams.grab_compute_capping_fps = 0.0f; // Using multi-threading in the component

[nseyffer]

That sounds good, thanks! I edited that line already and it works:
mInitParams.grab_compute_capping_fps = static_cast<float>(mVdPubRate);