Best DJI L1 Drone LiDAR Flight Parameters

The DJI Zenmuse L1 sensor has revolutionised drone LiDAR surveying, offering an accurate, affordable, lightweight and plug-and-play solution. 

But how do you actually use it to collect the best data for specific missions? 

This article highlights the recommended parameters for the L1, including the best parameters for industries/applications such as forestry and powerline inspection.

Once the data is collected, it can then be post-processed in DJI Terra for high-precision model reconstruction, and also in Terrasolid for further in-depth analysis. You can find out how to do this by reading our guide to post-processing in DJI Terra. 

Also, watch out for a forthcoming firmware update, that is currently at the BETA stage. It will allows for fully autonomous L1 missions with an oblique gimbal angle, something which is only currently available on standard nadir missions. heliguy™ will update on this in due course.

L1 Field Data Collection - Recommended Setup 

Ensure you are using the latest DJI L1 firmware version - v02.04.01.08 (correct as of October 1, 2021 - but check before use) - and then you can set your flight parameters. 

Setting Camera Parameters

Go to the camera view in DJI Pilot and select CAMERA.

If necessary, you can adjust the camera parameters - such as ISO, shutter and EV value - according to the surroundings, to create a good exposure for the photos. 

DJI L1 RTK and Base Station Satellite Data Acquisition

The D-RTK 2 Base Station or connection to NTRIP are both options available to receive positional corrections - something that is necessary for the L1. 

Go to camera view in DJI Pilot, select ···, then RTK, choose the RTK service type and ensure the status of RTK positioning and heading both display FIX.

Post-processing is also possible through a third-party base station, online source or a unconnected D-RTK 2. To do this:

1. Check the local operation time from the point cloud data file directory stored in the microSD card.

2. Search for .DAT format RTCM files of the same time as the stored files of the D-RTK 2 Mobile Station or third-party RTK base station. Rename the file as the same as the .RTB file in the point cloud data file directory and add a .RTCM suffix.

3. Copy the .RTCM file to the folder of the point cloud data file directory. DJI Terra will prioritise .RTCM files over .RTB files.

LiDAR Mapping And Setting Flight Parameters

This guide will help you create a Mapping Mission.

1. First, Plan the target area. In the DJI Pilot App, go to Mission Planning - Create a Route -Mapping and draw the target area on the map. Due to IMU calibration requirements every 100 seconds, the longest single flight route should not exceed 1000m (considering the recommended speed of 10m/s). If you have a large area, please split it into smaller zones.

2. Next, select Camera: Zenmuse L1 – LiDAR Mapping.

3. Calibration Flight: Needs to be turned on, in order to perform IMU calibration during the flight. More of this later.

4. Flight Route Altitude: 50-100m is recommended. Specific altitudes for specific missions will be discussed later in this blog.

5. Target Surface to Takeoff Point: You can keep default “0”.

6. Takeoff Speed (speed from the takeoff point to the first waypoint): You can keep the default 10m/s.

7. Flight Speed: 5 to 10m/s is recommended.

8. Upon Completion: Return To Home is recommended.

9. Advanced Settings:

   Side Overlap (LiDAR): 50% is recommended. Course Angle: You can keep the default; Margin: Can be set according to your need. Photo Mode: Can keep default “Time Interval Shot”.

10. Payload Settings:  Echo Mode: 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 for jobs such as a topographic survey or forestry. Sampling Rate: 160kHz for triple returns; 240kHz for dual returns; Scanning Mode: Repetitive scan is recommended for higher accuracy. More of this later; RGB Colouring: You need to turn this option on to obtain the colourised point cloud.

11. Save the mission.

12. Other settings: RGB camera setting: S mode (shutter priority) is recommended; you can adjust the parameters according to the environment - Mechanical Shutter and Dewarping should be enabled. RTK: You need to have RTK FIX during the flight to be able to make lidar post-processing and obtain the point cloud.

13. Pre-flight: Attach the L1 to the single downward gimbal on the M300 RTK. Power up the M300 RTK with L1 on the ground to warm up the system, and wait until the Payload INS IMU Warmed Up notification pops up in the app. This will take about five minutes.

14. Execute the mission.

15. Mission complete. You can now conduct post-processing with DJI Terra. You can find out more in our guide, here.

L1 Parameters By Specific Industry

The above overs an overview of the general recommended parameters for L1 data capture.

Below is a guide to L1 parameter settings for specific industries and applications, such as topographic mapping, forestry, powerline, and city modelling.  

Topographic Mapping Recommended Parameters

LiDAR is a powerful mapping solution for creating topographic models, such as Digital Elevation Models (DEM) and Digital Terrain Models (DTM).

The recommended parameters for topographic mapping with the L1 are:

• Mission Planning Methods: Aerial mapping (Terrain Follow if needed. See Terrain Follow section, below, for more details). Access via Mission Flight Screen in DJI Pilot. Tap and drag the area to be scanned on the map.

• Measurement Area Size: Each adjacent flight path does not exceed 1km

• Flying Height: 100m

• Flying Speed: 10m/s

• Side Overlap Rate: 50%

• Number of Echoes: Three echoes

• Sampling Frequency: 160K/s

• Scan Mode: Repeat scan

• Whether to turn on visible light coloring: On

Forestry Mapping Recommended Parameters

A LiDAR-equipped drone enables foresters to measure canopy heights, coverage, tree density and even measure the location and height of individual trees.

The recommended parameters for forestry mapping with the L1 are:

• Mission Planning Methods: Aerial mapping (Terrain Follow if needed. See Terrain Follow section, below, for more details). Access via Mission Flight Screen in DJI Pilot. Tap and drag the area to be scanned on the map.

• Measurement Area Size: each adjacent flight path does not exceed 1km

• Flying Height: 100 to 150m

• Flying Speed: 10m/s

• Side Overlap Rate: 50%

• Number of Echoes: Three echoes

• Sampling Frequency: 160K/s

• Scan Mode: Repeat scan

• Whether to turn on visible light coloring: On

Powerline Mapping Recommended Parameters

LiDAR is a useful solution for powerline mapping. LiDAR sensors capture the coordinates of the power line, electrical facilities, vegetation and ground objects in a single scan to significantly improve the inspection efficiency, and can be used to extract and generate 3D digital models. 

The recommended parameters for mapping powerlines with the L1 are:

• Mission Planning Methods: Linear Flight (KML importing/waypoint mission). Access via Mission Flight Screen in DJI Pilot. Tap and drag the area to be scanned on the map. See Linear Flight section, below, for recommended Linear Flight settings.

• Flight Path: Single flight path

• Flying Height: 50 meters above the top of the tower

• Flying Speed: 8m/s

• Waypoints Limitation: Less than 800m

• Number of Echoes: Two echoes

• Sampling Frequency: 240K/s

• Scan Mode: Non-Repeat scan

• Whether to turn on visible light coloring: On

City Modeling Recommended Parameters

LiDAR has emerged as an accurate, fast and versatile technique for town planning. For instance, 3D models which accurately reflect landform and architectural information help urban planners design and plan more effectively.

The recommended parameters for mapping powerlines with the L1 are: 

• Mission Planning Methods: Oblique missions, in most cases 4 oblique missions are enough. Access via Mission Flight Screen in DJI Pilot. Tap and drag the area to be scanned on the map.

• Measurement Area Size: each adjacent flight path does not exceed 1km

• Flying Height: 100m

• Flying Speed: 10m/s

• Side Overlap Rate: 50%

• Number of Echoes: Two echoes

• Sampling Frequency: 240K/s

• Scan Mode: Non-repeat scan

• Whether to turn on visible light coloring: On

• Gimbal Angle: -60 degree to -45 degree

Terrain Follow

For a Terrain Follow mission, a DSM file including the elevation information of the terrain needs to be imported.

The DSM file used for Terrain Follow Mission must use the WGS84 coordinate system, rather than projected coordinates. The file should not exceed 20 MB in size.

Terrain Follow is recommended when the elevation difference of the survey area is greater than 100 metres.

In a Terrain Follow Mission, an automatic Calibration Flight is not available, so it is necessary to perform manual calibration before and after the flight.

Linear Flight Mission

Enter the mission flight screen in DJI Pilot, select Create a Route and then choose a Linear Flight mission.

Tap and drag on the map to adjust the area that will be scanned.

Edit the parameters for a LiDAR mapping mission or Photogrammetry mission.

For LiDAR mapping: Ser the advanced settings, payload, flight band, flight route and other parameters.

It is recommended to enable Single Route. Set the flight altitude to 50-100m, the flight speed to 5-10m/s, and adjust the extension length to cover the area to be scanned.

For Photogrammetry mission: Set the advanced settings, payload settings, and other parameters.

It is recommended to disable Dewarping and set Forward Overlap (Visible) and Side Overlap (Visible) to default parameters.

L1 For Photogrammetry

As well as having a LiDAR module, the L1 also boasts a 20MP RGB camera, meaning it can also be used for photogrammetry.

If you want to use it strictly for photogrammetry, then it is important that the option L1 Photogrammetry is selected.

The L1 will not scan point cloud data during the mission and only the mapping camera will be operating.

Manual Flights

Operators can also conduct manual flight with the L1.

L1 parameters can be set in MENU. The recommended parameter values are:

• Non-repetitive scan

• Dual-echo

• 240 kHz Sample rate

• RGB colouring" on

• 3s as the shooting interval

Ensure that the Ntrip is properly connected or an RTK base station has been set up before the flight.

RGB colouring means that the L1’s visible-light camera takes photos concurrently to collecting LiDAR point cloud data. We recommend always enabling this option except during nighttime operations.

Prior to flight, ensure the L1 has performed a calibration flight. To do this, tap CAMERA and then the figure of 8 icon and finish the prompts to finish the calibration. 

Point Cloud Record On Manual Flights

Fly the drone near the target area and adjust the gimbal to a proper data-collection angle.

Then click LIDAR to go to the point cloud screen. Click the point cloud recording button to start recording. Press again to stop recording.

During manual flight, fly at a recommended speed of 8–12 m/s and a distance from the subject of 50–100 metres.

Tap the icon (pictured below and highlighted by the orange arrow) to view the point cloud model recorded in real-time during the flight.

During the flight, once the aircraft flies at a constant speed for 100 seconds, you need to pause the point cloud recording, perform the IMU calibration, and then resume it. 

It is recommended that another calibration flight be performed after recording the point cloud data.

L1 IMU Calibration

The accuracy of the inertial navigation system will continue to be lost during the uniform flight of the aircraft.

As far as the L1 is concerned, after 100 seconds of constant flight, the inertial navigation system's accuracy will drop below its nominal accuracy.

However, this can be restored through large speed changes. To enable this, the L1-M300 RTK will perform different manoeuvres at different stages of the flight, depending on the type of preset mission:

Mapping Mission:

Ensure that the Calibrate Flight button is on in the mission settings.

The inertial navigation calibration will accelerate and decelerate automatically at the starting point, end point and turning points (marked in yellow below) along the route, as this graphic shows:

**Corridor Mapping / Oblique Missions**

Ensure that the Calibrate Flight button is on in the mission settings.

Currently, Corridor mapping and Oblique missions will perform figure 8 calibration at the beginning and end of the mission, as this graphic shows:

Non-Repetitive Vs Repetitive Scan Modes

The L1 features two-point cloud scanning methods. Users can choose between non-repetitive and repetitive scanning methods.

The Non-repetitive scanning method is the L1's unique LiDAR technology. It provides a near-circular FOV with a dense scanning density in the centre of the FOV compared to the surrounding area.

In this scan mode, the vertical FOV is wider. This mode is recommended for capturing data on complex structures, such as building facades.

The repetitive scanning method provides a flat FOV, similar to traditional mechanical scanning methods. However, it can obtain more uniform and precise scanning results.

The vertical field is narrower in this scan mode, but the accuracy is higher. This mode is recommended for high-accuracy surveying and mapping.

The L1 is an accessible plug-and-play LiDAR solution, designed to streamline data collection. For more information, speak to one of our in-house GIS specialists. Contact us by phone or email.