User's Manual

Appendix II
Point Cloud Data Packet Absolute Time and Laser Firing Time Calculations
LiDAR transmits a GPS Data Packet and a Point Cloud Data Packet chronologically with μs timestamps from the same data source. The μs
timestamp in the Point Cloud Data Packet (GPS Timestamp) is used to calculate the packing time of this data packet.
There are two methods to calculate the absolute packing time of Point Cloud Data:
1) Retrieve the μs timestamp and the time information (UTC, decimal number) from the Point Cloud Data Packet. The absolute time of Point
Cloud Data Packet can be calculated by combining 2 parts: a) the 4 bytes μs timestamp; b) the 6 bytes UTC time information (decimal
number) in Point Cloud Data Packet.
2) First retrieve timestamp from the Point Cloud Data Packet, then retrieve time information (UTC) from the previous GPS Data Packet. The
absolute time of Point Cloud Data Packet can be calculated by combining 2 parts: a) the 4 bytes μs timestamp; b) the UTC time information
(decimal number) in previous GPS Data Packet.
NOTE
1) Because LiDAR GPS Data Packet is triggered by PPS rising edge, the corresponding GPRMC information (real absolute time) from GPS
module after PPS rising edge is not available at that time.
2) The UTC time in LiDAR GPS Data Packet and following Point Cloud Data Packet can only utilize previous GPRMC information, which is 1
full second older than the absolute time of the triggering PPS rising edge. But the LiDAR can automatically adjust and the user can simply
add the 4 bytes timestamp and 6 bytes UTC time to get absolute time.
3) Since every GPS Data Packet matches an internal 1Hz signal, the GPS Data Packet will be exported continuously in every second with or
without GPRMC information. If GPRMC is available, UTC time in data packets are updated according to GPRMC and avoid drift of internal
1Hz signal; if GPRMC is not available, UTC time in data packets are updated according to internal 1Hz signal and keep the mechanism.
NOTE Please refer to Appendix III for the calculation of absolute time using PTP protocol.
1 Absolute Time Calculation of Point Cloud Data Packet
The point cloud data packet absolute time calculations of Pandar20A and Pandar20B are the same, while the laser firing time calculations
are different. Pandar20A/B transmits two types of UDP Data Packet, including the point cloud UDP Data Packet and the GPS UDP Data
Packet, hereafter referred to as Point Cloud Data Packet and GPS Data Packet.
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