Dji Zenmuse l1 User manual

DJI L1 Operation Guidebook

V1.1 (June-2022)

 
 http://www.dji.com/zenmuse-l1 
 Copyright © 2022 DJI All Rights Reserved. 2 
 
Contents 
Supported Firmware and Software Versions ............................................................................................................. 4 
Parameter Overview........................................................................................................................................................... 4 
1 Introduction to DJI L1 ............................................................................................................................................. 4 
2 Specifications.............................................................................................................................................................5
3 Key Parameters.........................................................................................................................................................7
3.1 Detection Range...........................................................................................................................................7
3.2 Point Cloud Data Rate...............................................................................................................................7
3.3 Scan Mode and FOV................................................................................................................................. 8 
3.4 Beam Divergence Angle.........................................................................................................................10 
3.5 Ranging Accuracy .....................................................................................................................................10 
DJI L1 Field Operation Guide ........................................................................................................................................10 
1 RTK/PPK.....................................................................................................................................................................10 
1.1 Ntrip (Custom Network RTK) Solution................................................................................................10 
1.2 D-RTK 2 Base Station Solution............................................................................................................... 11 
1.3 Third-party RTK Solution.......................................................................................................................... 11 
2 IMU Calibration.......................................................................................................................................................13 
2.1 Calibration Flight Button in Manual Flight .......................................................................................13 
2.2 IMU Calibration in Mapping/Oblique/Linear Flight Missions..................................................14 
2.3 IMU Calibration in Waypoint Flight Missions.................................................................................15 
3 RGB Camera Recalibration.................................................................................................................................16 
3.1 Calibration data collection......................................................................................................................16 
3.2 Use DJI Terra software to generate the calibration files...........................................................17 
3.3 Run the calibration files in L1 ................................................................................................................18 
3.4 How to restore factory parameters? .................................................................................................18 
4 Flight Mission Planning........................................................................................................................................19 
4.1 Topographic Surveying............................................................................................................................19 
Terrain-follow Flight............................................................................................................................................21 
4.2 Riverbank / Road Surveying ................................................................................................................25 
4.3 Powerline ....................................................................................................................................................27 
5 Checkpoint Setup ................................................................................................................................................ 30 
5.1 3D Checkpoints ........................................................................................................................................ 30 
5.2 Elevation Checkpoints ...........................................................................................................................32 
6 Field Data Collection.........................................................................................................................................33 
6.1 Power on L1 for Warmup........................................................................................................................33 
6.2 Flight Mission Execution .......................................................................................................................33 
6.3 Manual Data Collection .........................................................................................................................34 
7 Data Storage ...........................................................................................................................................................36 
Processing L1 Data with DJI Terra ..............................................................................................................................36 
1 Prepare Your Computer......................................................................................................................................36 
2 Reconstruction Steps...........................................................................................................................................37 

 
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 Copyright © 2022 DJI All Rights Reserved. 3 
3 Result Files...............................................................................................................................................................43 
4 FAQ............................................................................................................................................................................45 
4.1 Error Message: The LiDAR point cloud POS data is abnormal...............................................45 
4.2 Error Message: The raw data is missing or the file path is wrong.........................................45 
4.3 Error Message: The raw data of the LiDAR point cloud is abnormal...................................46 
4.4 Error Message: LiDAR point cloud accuracy optimization failed. .........................................46 
4.5 Error Message: LiDAR point cloud POS calculation failed. .....................................................46 
4.6 Issue: Quality of point cloud model is poor, or the result has severe data loss...............46 
4.7 How to achieve a good vertical accuracy?.....................................................................................47 
 
 
 

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1. Supported Firmware and Software Versions

Before you proceed, please confirm that your device's firmware/software version is the latest by

checking the Release Notes on DJI website:

https://www.dji.com/zenmuse-l1/downloads

https://www.dji.com/matrice-300/downloads

The latest firmware versions as of June, 2022 are shown in the table below and are used as the basis

for the information within this guidebook. This guidebook will be updated to reflect changes from

future firmware updates.

M300 RTK Aircraft

V04.00.03.00

M300 RTK Remote Controller

V04.00.03.00

Pilot App

V4.0.1.21

Zenmuse L1

V04.00.01.06

DJI Terra

V3.1.4

Note: The parameters provided in this guidebook are for reference only and do not apply to all

scenarios. Please adjust them as appropriate to suit the actual conditions.

2. Parameter Overview

2.1 Introduction to DJI L1

The Zenmuse L1 integrates a Livox LiDAR module, a high-accuracy IMU, and a camera with a 1-inch

CMOS on a 3-axis stabilized gimbal. When used with Matrice 300 RTK and DJI Terra, the L1 forms a

complete solution that gives you real-time 3D data throughout the day, efficiently capturing the

details of complex structures and delivering highly accurate reconstructed models.

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Figure: L1 components

2.2 Specifications

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2.3 Key Parameters

2.3.1 Detection Range

This refers to the farthest measurable distance of the LiDAR. This parameter varies greatly based on

the actual environmental conditions. Main influencing factors include the target's surface reflectivity,

the target's shape, and ambient light interference. Manufacturers generally indicate the LiDAR's

measurable distance under different illumination and reflectivity. In the case of DJI L1, its LiDAR

supports a measurable range of 450 meters under 0 klx when the measured target's reflectivity is

80%, and 190 meters under 100 klx when the measured target's reflectivity is 10%.

"450 m @ 80%, 0 klx" means that, when the solar illuminance is 0 klx and the measured target's

reflectivity is greater than 80% (the reflectivity of a concrete floor or a road surface is 15%–30%, and

the reflectivity of a white plaster wall is 90%–99%), the maximum measurable distance is 450 m.

"190 m @ 10%, 100 klx" means that when the solar illuminance is 100 klx and the measured target's

reflectivity is greater than 10% (the reflectivity of a concrete floor or a road surface is 15%–30%, and

the reflectivity of a white plaster wall is 90%–99%), the maximum measurable distance is 190 m.

Most LiDAR sensors on the market use diffuse reflection objects (with a reflectivity of 90%) as the

testing benchmark. However, this parameter has limited practical significance. The measurable

distance at a reflectivity of 10% has greater practical significance.

2.3.2 Point Cloud Data Rate

Point cloud data rate is also called sampling frequency or pulse frequency. It refers to the maximum

number of laser beams emitted by the laser within a unit of time. Given the same conditions, a higher

frequency means a higher number of measured points and a higher operating efficiency.

The L1's point cloud data rate is affected by which echo mode is used. Three echo modes are

available: single-echo, dual-echo, and triple-echo mode. In single-echo or dual-echo mode, the

maximum sampling frequency is 240 kHz (that is, 240,000 laser beams emitted per second). In triple-

echo mode, the maximum sampling frequency is 160 kHz. Theoretically, the maximum number of

points measured per second in the dual-echo or triple-echo mode is 480,000. In practice, the number

of points measured in the second and third echoes are very small. The number of measured points is

the highest at a sampling frequency of 240 kHz in dual-echo mode. Therefore, it is recommended to

choose the dual-echo mode if you need more measured points, or choose the triple-echo mode if you

need higher penetration.

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2.3.3 Scan Mode and FOV

The L1 can produce different scan shapes in different scan modes. Please note that the shape formed

by the LiDAR on the ground is determined by the laser scan mode, the flight direction and speed, and

the terrain. The Livox LiDAR on DJI L1 supports non-repetitive scan mode and repetitive scan mode.

Figure: Scan shapes formed in 0.1s with repetitive scan mode of L1

Figure: Scan shapes formed in 0.1s, 0.2s, 0.5s, and 1s with non-repetitive scan mode of L1

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Field of view (FOV), also known as the scan angle, represents the angle covered by the LiDAR sensor,

or the angle at which laser signals are emitted. The FOV of L1 varies in different scan modes

Repetitive scan: FOV 70.4°*4.5°. In this scan mode, the vertical field is narrower, but the accuracy is

higher. This mode is recommended for high-accuracy surveying and mapping.

Figure: Scan angle in repetitive scan mode

Non-repetitive scan: FOV 70.4°*77.2°. In this scan mode, the vertical FOV is wider. This mode is

recommended for data capturing of complex structures, such as building facades.

Figure: Scan angle in non-repetitive scan mode

Note:

The effective range of L1 varies based on where the object is within the FOV. The closer to the edge

of the L1's FOV, the shorter the effective range.

The closer to the center of the L1's FOV, the farther the effective range. See the figure below for

details.

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Figure: Effective range of L1 within the FOV

2.3.4 Beam Divergence Angle

A divergence angle, if any, of the beams from the LiDAR can produce light spots which increase in

size as the distance increases.

2.3.5 Ranging Accuracy

Ranging accuracy refers to the discrepancy between the LiDAR-measured distance and the actual

distance. Ranging accuracy is different from system accuracy in that the former does not represent

the accuracy of the final result.

3. DJI L1 Field Operation Guide

3.1 RTK/PPK

For the purpose of point cloud data processing, L1 needs to have centimeter-accurate positioning

data with either RTK or PPK. The RTK FIX status needs to be maintained throughout the duration of

the L1 flight mission. If RTK connection stability cannot be guaranteed, PPK could also be used. The

detailed workflows of each method are described below.

3.1.1 Ntrip (Custom Network RTK) Solution

In the RTK settings page of the DJI Pilot App, you can choose Custom Network RTK, and enter the

NTRIP account information to connect to the Ntrip service. (Note: The remote controller must be

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connected to the internet through WiFi or the 4G dongle). If the Ntrip service is connected and the

RTK status is FIX throughout the flight, the base station file will be automatically saved in the results

file.

3.1.2 D-RTK 2 Base Station Solution

Set up D-RTK 2 at a known point. Switch the D-RTK 2 to Mode 5. In the RTK settings page of the DJI

Pilot App, select D-RTK 2 as RTK Service Type. Then link the aircraft to the D-RTK 2. In the RTK

settings page, go to the Advanced Settings (Pin: 123456 by default). Modify the D-RTK 2's

coordinates to the coordinates of the known point.

When high absolute accuracy is needed, you must set up the D-RTK 2 at a known point instead of

directly using its self-convergent GNSS coordinates. This is because the static convergent coordinates

of the D-RTK 2 have an error in the meter-level. If the D-RTK 2 position is not corrected with known

coordinates, the absolute accuracy of the result cannot be guaranteed and the point cloud data from

multiple flights might not be consistent.

Note when setting up the D-RTK2 at a known point it is important to add the rod height. When post

processing, the default output will be WGS84 unless otherwise selected.

After setting up the D-RTK 2 base station, you can connect the aircraft to the D-RTK 2 for the flight

mission.

Alternatively, you can use the PPK method where no real-time connection between the drone and the

D-RTK 2 is required. With the PPK method, the distance between the D-RTK 2 and the aircraft is

recommended to be within 10km. Select "None" in the RTK service type. Turn off the RTK Positioning

switch to go to GNSS flight mode. After data collection for the mission is completed, use a Type C

cable to connect the D-RTK 2 to a PC. Copy the base station file with a suffix of .DAT for the

corresponding time slot and paste the file in the same folder as L1’s result file. In this way, DJI Terra

will use the D-RTK 2 data for PPK processing to calculate the accurate POS data.

3.1.3 Third-party RTK Solution

A third-party RTK base station device can also be used for PPK. In this case, no connection is required

between the drone and the RTK base station. The distance between the third-party RTK base and the

aircraft is recommended to be within 10km. After the flight is completed, search for the base station

file for the corresponding time slot and rename the file following the suffix rules below. Then, copy

the base station file to the same directory as the LiDAR files. If the third-party RTK base station has no

coordinates input for the known point, you can open the .O base station file in text form and modify

the "APPPO POSITION XYZ" value to be the corrected coordinate of the RTK base in the ECEF

coordinate system.

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The L1 supports the following base station protocols and versions. (Note: The name of the renamed

file DJI_YYYYMMDDHHMM_XXX should be consistent with the name of the .RTK file in the point

cloud data directory). If there is a .RTB file in the same directory, it needs to be deleted.

Data format

Version

Message

Rename to

Rinex

V2.1.x

DJI_YYYYMMDDHHMM_XXX.obs

V3.0.x

RTCM

V3.0

1003, 1004, 1012,

1014

DJI_YYYYMMDDHHMM_XXX.rtcm

V3.2

MSM4, MSM5,

MSM6, MSM7

OEM

OEM4

RANGE

DJI_YYYYMMDDHHMM_XXX.oem

OEM6

RANGE

UBX

RAWX

DJI_YYYYMMDDHHMM_XXX.ubx

Table: RTK protocol types supported by L1

Note: Base station files are necessary for L1 data processing. If neither Ntrip nor PPK files exist, L1

data cannot be processed. If the RTK is disconnected during the flight, the mission will be

automatically paused to ensure data validity.

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3.2 IMU Calibration

IMU calibration is a prerequisite for LiDAR accuracy. It is a key factor that impacts the final point

cloud accuracy. For the L1, please note that IMU calibration is required before, during (every 100s of

the flight mission), and after data collection to ensure the inertial navigation system accuracy.

Figure: IMU calibration is needed before, during, and after the flight

Below are two ways of IMU calibrations that can be used during manual/mission (flight route) flight.

3.2.1 Calibration Flight Button in Manual Flight

Fly the drone to a proper altitude, switch to the camera screen, and click on the "Calibration Flight"

button. M300 RTK will automatically fly forward and backward 3 times to calibrate the IMU system at

current altitude. Make sure there are no obstacles in the 30m range ahead of the drone.

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Figure: Manual IMU Calibration Option

3.2.2 IMU Calibration in Mapping/Oblique/Linear Flight Missions

In mapping/oblique flight missions, you can find the toggle “IMU Calibration”. When turned on,

acceleration and deceleration calibration flights will be inserted to the flight route at the starting

point, the ending point, turning points, and along the route (every 100s). The calibration routes are

shown in yellow in the figure below.

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Figure: Calibration flight route

For a linear flight mission, the calibration flight route is inserted automatically to the beginning, during

the mission (every 100s between two waypoints) and the end of the flight routes.

3.2.3 IMU Calibration in Waypoint Flight Missions

In waypoint flight missions, you can find the IMU Calibration option in the route parameters.

Figure: IMU Calibration option in a waypoint flight mission

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In the waypoint settings, you would need to add the action “Start point cloud modeling recording” at

the waypoint you want to start at, and add the action “Finish point cloud modeling recording” at the

point you would like to end at. In this case, if the IMU Calibration option is turned on, you’ll find the

IMU calibration section inserted automatically to the flight route (shown in yellow).

Figure: IMU calibration inserted to waypoint flight mission (Start point cloud modeling at Waypoint 1 and finish

at Waypoint 5)

3.3 RGB Camera Recalibration

When the L1 has regular colorization issues, such as multiple lines appearing in the point cloud with

ghosting effect, the user will need to recalibrate the internal and external parameters of the RGB

camera of L1 following the below steps. Before you start please check your firmware versions

referring to Section 1. Supported Firmware and Software Versions.

Note: This is a premium feature included in DJI Terra Pro and more advanced versions.

3.3.1 Calibration data collection

Create a 2D Mapping mission in DJI Pilot App and draw an area of around 200m*200m; The area

should have vertical structures like buildings;

Camera type: Zenmuse L1 - Lidar Mapping;

Flight Route Altitude: 100m;

Speed: 10m/s;

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Enable the “Elevation Optimization” option;

In Advanced Settings, Side Overlap: 50%;

In Payload Settings, select “Single Return”, “240 kHz” and “Repetitive Scan”, and enable the “RGB

Coloring” option;

Save the mission;

In L1 camera settings, disable the camera dewarping;

Figure: Dewarping Option in the Camera Settings

Execute the flight mission and obtain the raw data files collected by L1 and check whether the

images are clear and sharp, if not they cannot be used for calibration.

3.3.2 Use DJI Terra software to generate the calibration files

Use DJI Terra version 3.1.0 or above to create a new “LiDAR Point Cloud Processing”

reconstruction mission;

Import the dataset collected by defining the dataset directory and changing the “Scenarios”

option to “Zenmuse L1 Calibration”;

Start processing in Terra;

When the reconstruction is completed, please check if the point cloud model colorization is ok or

not. If there are still multiple layers or ghosting effects, please repeat step 1) and 2). If the result is

ok, you can proceed to use the calibration files from this mission;

The calibration file with suffix “.tar” can be found under the PROJECT/lidars/terra_L1_cali”

directory as shown below:

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Figure: Calibration File Directory

3.3.3 Run the calibration files in L1

Store the calibration file under the root directory of a microSD card and insert into the L1, connect

L1 to a M300 RTK and power on the M300 RTK. Wait for about 5 minutes to complete the

calibration. There is no App notification during the calibration currently.

To confirm the calibration process is completed: remove the microSD card from the L1, open the

log file with suffix “.txt”, the calibration process is successful if the log file shows “all succeed”.

Figure: The txt file will show “all succeed” if the calibration is successful

3.3.4 How to restore factory parameters?

In case you need to restore the factory parameters of the L1 sensor, please follow below steps:

Create a new .txt text file, and name it as reset_cali_user. Open the file and write the SN serial

number of the L1 that needs to be reset, with the format of “SN number: XXXXXXXXXXXXXX”

(find the SN serial number in the .CLI file that’s saved on the microsd card, or view in the device

version information in Pilot app by going to the three dots in the right in manual flight, the three

dots sub menu, then About).

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Copy the .txt text file to the root directory of the microSD card, insert the microSD card into the

L1 that needs to be calibrated, install the L1 onto the M300 RTK and power on the aircraft, wait

about 5 minutes to complete the calibration.

Record a set of point cloud data, remove the microSD card from the L1. Connect it to a computer

and check the .txt format log file. If it displays all succeeded, the reset is successful. Users can also

check whether the time parameter of the .CLI file is restored to the factory time.

3.4 Flight Mission Planning

A flight mission of the survey area can be pre-planned with the DJI Pilot App to enable automatic data

capture of a polygon area or a strip area. Detailed parameter recommendations for typical scenarios

are as below:

3.4.1 Topographic Surveying

This is a typical scenario of LiDAR to generate topographic maps, contour lines, etc. It may also be

applicable to forest inventory monitoring by measuring the tree heights and density of the canopy.

Create a "Mapping Mission". You can import the KML file of the target area or manually draw the area

on the map. The recommended parameter settings for topographic surveying are as follows:

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