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Appendix II Absolute Time and Laser Firing Time
■ Absolute Time of Point Cloud Data Packets
The Body of each Point Cloud Data Packet contains 2 data blocks, detailed in Section 3.1.2 (Point Cloud UDP Data).
Single Return Mode
The measurements from one round of firing are stored in one block.
The absolute time of a Point Cloud Data Packet is the time when the LiDAR sends a command to trigger a round of firing that will be stored in
Block 2.
Dual Return Mode
The measurements from one round of firing are stored in the two blocks of one packet.
The absolute time of a Point Cloud Data Packet is the time when the LiDAR sends a command to trigger a round of firing that will be stored in
Blocks 1 & 2.
Calculation
The absolute time of a Point Cloud Data Packet is the sum of date, time (accurate to the second) and μs time.
· Date and Time: can be retrieved either from the current Point Cloud Data Packet (6 bytes of Date & Time), or from the previous GPS Data
Packet (6 bytes of Date and 6 bytes of Time).
· μs time: can be retrieved from the current Point Cloud Data Packet (4 bytes of Timestamp)
NOTE When using a PTP clock source, the LiDAR does not output GPS Data Packets.