Synchronization

We synchronize all sensors in the sensor suite at the hardware level. To this end, we utilize Precision Timing Protocol (PTP) and the generalized Precision Time Protocol (gPTP), which can provide sub-microsecond synchronization accuracy in the Ethernet.

The time synchronization among all the devices is illustrated in Fig. 1. First, we use a PTP server to synchronize GNSS’s clock with the system clock of the industrial personal computer (IPC). The IPC is then designated as the master clock, using the PTP protocol to synchronize with the RGB cameras. Since the Livox HAP only supports the gPTP protocol, we use gPTP to synchronize between the IPC and the LiDAR. To synchronize the event cameras with the system time, we utilize a micro-controller to generate four synchronization pulses at 20 Hz. These pulses are used to simultaneously trigger the two RGB cameras and the two event cameras. The RGB and event cameras are configured in external trigger mode. When the RGB camera receives a synchronization pulse, it begins to capture an image and record its timestamp. Meanwhile, the event camera would also be triggered by the synchronization pulse, immediately generating a signal with a timestamp. The temporal offset between the RGB camera and the event camera can be easily calculated as the difference between the two timestamps. In addition, the integrated navigation systems UG005 X1 and CGI-610 are synchronized via their built-in GNSS clocks.