Appendix B: Absolute time of point cloud data
B.1. Source of absolute time
The lidar retrieves the current absolute time by connecting to an external clock source.
B.1.1. GPS as the clock source
The lidar connects to a third-party GPS module to obtain pulse-per-second (PPS) signals and NMEA sentences.
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NMEA sentence ($GPRMC or $GPGGA) can be selected using web control or PTC commands.
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The signal status of GPS PPS and NMEA can be checked using web control or PTC commands.
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The timing requirements of PPS and NMEA are shown in Section 2.2.1 Pin description.
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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.
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The timing requirements of PPS and NMEA are shown in Section 2.2.1 Pin description.
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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 and time (accurate
to the second)
Lidar behavior
Unlocked (Initial) Virtual Since the lidar has not been locked before, it starts counting from a virtual UTC (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, the lidar obtains the actual date and time by
performing these two steps:
1. Extract the date and time from the previous NMEA message.
2. Add 1 full second.
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