Livox Mid-70 User Manual page 16

Livox Mid-70 User Manual
Tags: Indicates the return type of the laser and if the point detected is a noise. The format of the tag is as
shown below:
bit7 bit6
Point property based
o n n e a r b y w a v e f o r m
distortion:
00: Normal
01: Nearby waveform
distortion
10: Reserved
11: Reserved
Each tag is composed of one byte. In this byte, bit7, and bit6 are Group 1, bit5 and bit4 are Group 2, bit3 and
bit2 are Group 3 while bit1 and bit0 are Group 4.
Group 1 indicates if the sampling point is a noise based on the nearby waveform distortion. Due to the optical
system characteristics of the machine, nearby return signal will be distorted by the stray light inside the system,
leading to unreliable depth calculation results (especially when the return signal energy is small). "01" indicates
that nearby return signal is distorted; "00" indicates that waveform is normal.
Group 2 indicates the return sequence of the sampling point. Featuring a coaxial optical path, the Mid-70 itself
will generate a laser return even if there is no detectable object around. This return is recorded as return 0. After
that, if there is any object within the detectable range, the first laser that returns to the Mid-70 is recorded as
return 1, and then return 2, and so on. If the object is too close to the Mid-70, such as 1.5 m away, the first
effective return will be merged into return 0, and be recorded as return 0.
Group 3 indicates if the sampling point is a noise based on the intensity of the return. Normally, the intensity
of the returns of the noises generated due to the interference of atmosphere particles such as dust, rain, fog,
and snow is quite low. Therefore, the noises are divided into two categories based on the intensity of the return
received. "00" stands for normal point cloud; "01" stands for low intensity of the return, indicating that the
samples have a high possibility of being noises such as dust, rain, and fog. The lower the confidence level of
the sample is, the lower the possibility that it is a noise.
Group 4 indicates if the sampling point is a noise based on its spatial position. Normally, when the Mid-70 sensors
detect two objects in close proximity of each other, there will be some thread-like noises between the two
objects. The noises are divided into three categories. The lower the confidence level of the noise is, the lower
the possibility that it is noise.
Timestamp
There are three ways to synchronize data with the Mid-70: IEEE 1588-2008, Pulse Per Second (PPS), and GPS
(PPS+UTC).
IEEE 1588-2008: IEEE 1588-2008 is the Precision Time Protocol (PTP) enabling precise synchronization of
clocks in measurement and control systems by Ethernet. Livox LiDAR sensors, as the ordinary clock in the PTP,
only supports UDP/IPV4 for PTP. Livox LiDAR sensors support the following message events: Sync, Follow_up,
Delay_req, and Delay_resp.
PPS: PPS uses the sync cable for data synchronization. Refer to the Cables section for more information. The
synchronization logic is shown in the figure below. The pulse interval in PPS is 1s (t0 = 1000 ms) while the
continuous time of high-level voltage is from 20 ms to 200 ms (20 ms <t1<200 ms). The rising edge of PPS
resets the timestamp to zero, so the timestamp of the point cloud data indicates the duration between the point
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bit5 bit4
Return number:
00: return 0
01: return 1
10: return 2
11: Reserved
bit3 bit2
Point property based on
intensity:
00: Normal
01: Noise that does not meet
intensity expectations
10: Reserved
11: Reserved
bit1 bit0
Point property based on
spatial position:
00: Normal
01: High confidence level of
the noise
10: Moderate confidence
level of the noise
11: Low confidence level of
the noise