Hesai Pandar64, User Manual

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Appendix II Absolute Time of Point Cloud Data
■ Source of Absolute Time
The lidar retrieves the current absolute time by connecting to an external clock source (GPS/PTP).
Users can select the clock source, see Section 4.2 (Web Control - Settings).
1) GPS as the Clock Source
· The lidar connects to a third-party GPS module to obtain the PPS (pulse-per-second) signal and the NMEA sentence ($GPRMC or $GPGGA).
· Users may select either $GPRMC or $GPGGA sentences, see Section 4.2 (Web Control – Settings).
· Users may check the signal status of GPS PPS and NMEA, see Section 4.1 (Web Control - Home).
· The timing requirements of PPS and NMEA are shown in Section 2.2.1 (Pin Description).
· Each rising edge of the lidar's internal 1 Hz signal triggers a GPS Data Packet. The data format is detailed in Section 3.2 (GPS Data Packet).
The absolute time is updated as follows.
NMEA
status
Date & Time
(accurate to the second)
Lidar behavior
Unlocked Virtual Starts counting from a virtual UTC time (such as 2000-01-01 00:00:00) using the lidar's internal 1 Hz
signal.
Locked Synchronized At each rising edge of the internal 1 Hz signal, obtain the actual date and time by
· extracting the date and time from the previous NMEA message, and
· automatically adding 1 full second.
Lost Drifting Starts counting from the last synchronized time, using the lidar's internal 1 Hz signal.
Will gradually drift from the actual GPS time.