Global Time Accuracy

[EthabKim]

Hi, I am using realsense d455 cameras and need to do sensor fusion with a LiDAR. I am curious about using global time on the cameras. It is my understanding that global time syncs hardware stamps onto host time by using a regression model. I am wondering if there are estimates on the accuracy of this synchronization (eg ~5ms) and if this is generally constant? I have looked at a few other discussions, but it has generally been unclear to me what the expected accuracy of global time on the d455s is.

[MartyG-RealSense]

Hi @EthabKim The best available reference about how Global Time functions can be found at #3909 - however, there is not information available about a specific accuracy value for the synchronization. Accuracy is discussed in that link though.

If ROS is used for the sensor fusion then Global Time does not have to be used, as ROS has its own timing sync mechanism and so Global Time can be disabled.

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If you are not using ROS, a way to sync a RealSense camera with a lidar camera without using Global Time is to attach sync cable wiring between the physical sync pins on the RealSense camera (which are underneath a removable cap on the top of the camera casing) and the lidar. You can then enable a RealSense option called Output Trigger Enabled that causes the camera to generate a sync trigger pulse on every frame and transmit the trigger through the wire.

The main challenge then becomes how to attach the physical wiring to the lidar in a way that results in the lidar being synced with the D455 by the trigger pulses.