9.3.1.1 Firing Sequence
A firing sequence occurs when all the lasers in a sensor are fired. They are fired in a sequence specific to a given product
line or model. Laser recharge time is included. A firing sequence is sometimes referred to as a firing group. A firing
sequence is not allowed to span multiple data packets.
On average, it takes 53.3 μs to fire all 128 lasers in a VLS-128 and recharge. VLS-128 sensors fire their lasers in groups of
eight.
9.3.1.2 Laser Channel
A laser channel is a single 903 nm laser emitter and detector pair. Each laser channel is fixed at a particular elevation angle
relative to the horizontal plane of the sensor. Each laser channel is given its own Laser ID number. Since the elevation
angle of a particular laser channel doesn't change, it doesn't appear in data packets. Its value is inferred by a data point's
location in a data packet.
In VLS-128 sensors, no laser channels are inline (vertically) with the Azimuth in a firing sequence. Instead, each channel is
offset by one of eight different offsets.
9.3.1.3 Data Point
A data point is a measurement by one laser channel of a reflection of a laser pulse.
A data point is represented in the packet by three bytes - two bytes of distance and one byte of calibrated reflectivity. The
distance is an unsigned integer. It has 4 mm granularity. Hence, a reported value of 25,154 represents 100,616 mm or
100.616 m. Calibrated reflectivity is reported on a scale of 0 to 255 as described in
Calibrated Reflectivity on page 31
. The
elevation angle (ω) is inferred based on the position of the data point within a data block.
A distance of 0 indicates a non-measurement. The laser is either off or a measurable reflection was not returned in time.
9.3.1.4 Azimuth
A two-byte azimuth value (α) appears after the flag bytes at the beginning of each data block. The azimuth is an unsigned
integer. It represents an angle in hundredths of a degree. Therefore, a raw value of 27742 should be interpreted as
277.42°.
Valid values for azimuth range from 0 to 35999. Only one azimuth value is reported per data block.
9.3.1.5 Data Block
The information from one firing sequence of 128 lasers is contained in four consecutive data blocks in Single Return mode,
or eight consecutive data blocks in Dual Return mode. Each data packet has up to three firing sequences.
Only one Azimuth is returned per data block.
A data block consists of 100 bytes of binary data:
A two-byte flag (0xFFEE)
A two-byte Azimuth
32 Data Points
[2 + 2 + (32 × 3)] = 100 bytes
For calculating time offsets it is recommended that the data blocks in a packet be numbered 0 to 11.
9.3.1.6 Time Stamp
The four-byte time stamp is a 32-bit unsigned integer marking the moment of the first data point in the first firing sequence
of the first data block. The time stamp’s value is the number of microseconds elapsed since the top of the hour. The num-
ber ranges from 0 to 3,599,999,999, the number of microseconds in one hour.
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VLS-128 User Manual
DRAFT