L515 global timestamps

[matthiasverstraete]

Required Info
Camera Model	L515
Firmware Version	01.05.08.01
Operating System & Version	Linux (Ubuntu 18.04)
Kernel Version (Linux Only)	5.4.0-96-generic
Platform	PC
SDK Version	2.49.0 }
Language	python
Segment	others

Issue Description

I want sync multiple L515 cameras. Therefore I need a global timestamp for each frame. I already enabled the global_time with

sensor.set_option(rs.option.global_time_enabled, 1.0)

However, the timestamp I get is still in hardware clock (frame_set.get_frame_timestamp_domain()).

Is there something else I should do in order to get global timestamps?

A bonus question, is it correct that the L515 doesn't support sensor timestamp? This would be better for my use case, but if it's not possible, that's fine.

Thanks!

[MartyG-RealSense]

Hi @matthiasverstraete Do you have a patched kernel so that hardware metadata can be received? If you built librealsense from Debian packages or from source code using the RSUSB backend method then hardware metadata support should be included. If librealsense was built from source code using the instructions at the installation.md
page (a non-RSUSB installation method) then you would need to run a patch script - ./scripts/patch-realsense-ubuntu-lts.sh - in order for hardware metadata to be provided.

https://github.com/IntelRealSense/librealsense/blob/master/doc/installation.md

A RealSense team member describes in #2188 (comment) how sensor_timestamp requires the kernel patch.

Having said that, I do not have a reference that definitively states whether sensor_timestamp is available on L515. However, #8307 details how an L515 user had patched the kernel and still could not access sensor_timestamp. And a comparison of 400 Series vs L515 frame metadata in the RealSense Viewer shows that the 400 Series has the sensor timestamp listed but L515 does not.

400 Series

L515

If you wish to sync multiple L515 cameras, Intel provide a white-paper guide document for doing so.

https://dev.intelrealsense.com/docs/lidar-camera-l515-multi-camera-setup

[matthiasverstraete]

I installed librealsense as a pip package (pyrealsense2) so I don't know if this patch should be applied in that case?

Also, I can get the frame timestamp with frames.get_frame_metadata(rs.frame_metadata_value.frame_timestamp). However, it's always expressed in the hardware clock, while the documentation seems to indicate that if global time is enabled, that it should be expressed in the system clock. Or am I making wrong assumptions?

[MartyG-RealSense]

If you installed pyrealsense2 with pip packages using the command pip install pyrealsense2 then that would only install the RealSense Python compatibility wrapper pyrealsense2 and not the librealsense SDK.

If librealsense is installed from Debian packages using the instructions in the link below then metadata support should be included in the SDK build.

https://github.com/IntelRealSense/librealsense/blob/master/doc/distribution_linux.md

#4505 (comment) provides an excellent explanation of global time, describing the timestamps returned as the hardware timestamp synchronized with host time.

[MartyG-RealSense]

Hi @matthiasverstraete Do you require further assistance with this case, please? Thanks!

[matthiasverstraete]

Sorry for the late reply. I will be using the backend timestamp for now.
Thanks for the assistance.

[MartyG-RealSense]

No problem at all, @matthiasverstraete - thanks very much for the update!