Legend:
light blue: EIP+UDP packet header (42 bytes)
orange: Timestamp (4 bytes)
red: PPS status (1 byte)
green: NMEA GPRMC sentence (length varies)
9.4 Discreet Point Timing Calculation
For the purpose of geo-referencing LiDAR data, it is helpful to calculate the exact moment of a particular laser firing in
order to more closely associate it with time stamped data from an INS. By using the firing timing information given in
Figure
9-5 below
you are able to compute the exact firing time for each data point.
All 32 lasers are fired in pairs and recharged every 55.296 μs. The cycle time between firings is 2.304 μs. There are 16 fir-
ings (16 × 2.304 μs) followed by a recharge period of 18.43 μs. Therefore, the timing cycle to fire and recharge all 32 lasers
is given by (16 × 2.304 μs) + 18.43 μs = 55.296 μs.
Figure 9-5 Firing Sequence Timing
VLP-32C lasers are fired in pairs at widely separated angles to minimize IR crosstalk. The sequence of firings is specified in
Table 9-5 below
. The first pair to fire is lasers 0 and 1. The second are 2 and 3. And so on.
Firing
Order
Laser ID
Elevation
Angle (°)
Elevation
Angle (°)
Laser ID
0
0
-25
-1
1
1
2
-1.667
-15.639
3
2
4
-11.31
0
5
3
6
-0.667
-8.843
7
4
8
-7.254
0.333
9
5
10
-0.333
-6.148
11
6
12
-5.333
1.333
13
7
14
0.667
-4
15
8
16
-4.667
1.667
17
Table 9-5 VLP-32C's Lasers Fire in Pairs
62
VLP-32C User Manual
