User's Manual

61
Appendix II Absolute Time and Laser Firing Time
II.1 Absolute Time of Point Cloud Data Packets
The absolute packing 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, year, month, date, hour, minute, second), 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 The calculation of absolute time is different when PTP protocol is used. See Appendix III PTP Protocol.
II.2 End Time of Each Block
Assuming that the absolute packing time of a Point Cloud Data Packet is t0 (detailed in II.1), the end time of each block (the time when all the lasers finish
firing) can be calculated.
There are 10 blocks of ranging data in each Point Cloud Data Packet, as shown below. Each block contains the ranging data from 40 channels, one return
per channel.
Poind Cloud Data Packet – Ranging Data: 1240 bytes (10 blocks)
Block1
Block2
Block3
…
Block10
0xFFEE
0xFFEE
0xFFEE
…
0xFFEE
Azimuth 1
Azimuth 2
Azimuth 3
…
Azimuth 10
Channel 1
Channel 1
Channel 1
…
Channel 1
Channel 2
Channel 2
Channel 2
…
Channel 2
…
…
…
…
…
Channel 40
Channel 40
Channel 40
…
Channel 40