Is get_timestamp() aware of serial communication latency?

[amm385]

Required Info
Camera Model	D435
Firmware Version	don't have it on me :(
Operating System & Version	Ubuntu 18
Kernel Version (Linux Only)	4.9.140-tegra
Platform	NVIDIA Jetson
SDK Version	2.36.0
Language	python
Segment	Robot

Issue Description

Imagine I have a very long usb cable or a very unpredictable latency between my image being ready on the camera firmware and my pyrealsense sdk receiving the data. If I call get_timestamp(), I can imagine there being one of two values returned, depending on how get_timestamp syncs its clock with my system clock:

a) My host computer's timestamp when the frames were fully collected on the camera's firmware
b) My host computer's timestamp when the frames were received by the host computer

Which of those values is returned by get_timestamp?

If this doesn't make sense yet, here's an example:
The camera and my computer are clock-synced. The camera takes a picture at t=100ms.
It transmits this information back to the computer. This process takes 10ms.
So the SDK receives the full batch of data at t=110ms.

Does get_timestamp() return 100 or 110?

Or, alternatively, am I misunderstanding how this works? I did my best to parse the other questions on here but am still confused.

[MartyG-RealSense]

Hi @amm385 The documentation for get_timestamp() in the link below states that it retrieves the time at which the frame was captured. At runtime the SDK selects the most correct representation from the different types of timestamp available, based on both device and host capabilities.

https://intelrealsense.github.io/librealsense/doxygen/classrs2_1_1frame.html#a25f71d45193f2f4d77960320276b83f1

The timestamp timings of RealSense camera sensors are generated as frame metadata attributes. These can be produced by the camera firmware or by the host clock. The links below describe how metadata is created.

https://dev.intelrealsense.com/docs/frame-metadata

#2188 (comment)

Device time and system time are aligned when Global Time is enabled.

#3909

[amm385]

Thanks for your answer @MartyG-RealSense. Certainly a bit confusing but glad there are a variety of options to choose from.

[MartyG-RealSense]

You are very welcome @amm385 - good luck!