Velodyne VLS-128, User Manual, Page: 49 / 132

Chapter 8 •
Sensor Operation
This chapter provides details on the laser firing sequence, point density, and how to determine throughput rate and angu-
lar resolution.
8.1 Firing Sequence
49
8.2 Throughput Calculations 49
8.2.1 Data Packet Rate 49
8.2.2 Position Packet Rate 49
8.2.3 Total Packet Rate 49
8.2.4 Laser Measurements Per Second 50
8.3 Rotation Speed (RPM) 50
8.3.1 Horizontal Angular (Azimuth) Resolution 50
8.3.2 Rotation Speed Fluctuation and Point Density 51
8.1 Firing Sequence
All 128 lasers are fired and recharged every 53.3 μs on average. Lasers are fired in groups of eight. Each firing group
takes 2.665 μs to complete. There are 16 firing groups (16 × 8 = 128) total in a firing sequence. However, a maintenance
period of 2.665 μs is interposed between the 8th and 9th firing groups. After the 16th firing group there is a second, longer
maintenance period of 7.995 μs. Therefore, the timing cycle to fire and recharge all 128 lasers is given by (8 × 2.665 μs) +
2.665 μs + (8 × 2.665 μs) + 7.995 μs = 53.3 μs. This pattern is illustrated in
Figure 9-5 on page 61 .
8.2 Throughput Calculations
Some terms used here are defined in
Packet Types and Definitions on page 53
.
8.2.1 Data Packet Rate
There are 3 firing cycles in a data packet. 3 x 53.3 μs = 0.1599 ms is the accumulation delay per packet.
1 packet/0.1599 ms = 6253.9 packets/second
8.2.2 Position Packet Rate
Position packets arrive at approximately 1/14th the rate of data packets.
554 bytes/packet * 6253.9 packets/second / 14 = 247475.8 bytes/second
8.2.3 Total Packet Rate
Summing yields 8052343 bytes/second for single return mode.
Dual return mode doubles the data rate but not the position packet rate: (2 * 7804867.2 bytes/second) + 247475.8
bytes/second = 15857210.2 bytes/second
Chapter 8 • Sensor Operation 49
DRAFT