by Shannon Whitsett
Presented here is a full mission walkthrough of the DJI L2. We show the preparation, execution, and processing of a LiDAR mission with ground checks utilizing the DJI Zenmuse L2 payload and an Emlid Reach RS2+ base and Emlid RS3 rover. The software used in this walkthrough includes Emlid Flow, Emlid Flow 360, DJI Pilot 2, and DJI Terra. The equipment used includes the DJI Zenmuse L2, DJI RC Plus, DJI Matrice 300, and the Emlid Reach RS3 Base/Rover Essentials kit.
To begin, login to Emlid Flow 360 on a web browser and create a New Project that will contain your check shots. Manually add the known point for your base if you have it. Out in the field, set and level the base. Double check your settings and configuration are correct.
Setting up RS2+ base for check shots and logs
Open Emlid Flow on your mobile device to set Base output to LoRa radio. The base output should be over the LoRa radio so that the rover will receive corrections while you collect your check shots. Check your Logging settings to make sure you are recording the necessary data for post-processing the L2 data. Use Emlid Flow with a wifi connection to your RS2 in order to adjust the Logging settings. Select Autostart and Backup source date for RINEX. Tap Apply. Then import your known point for the base. In the Base Settings, change the coordinate entry method to Manual and input your pole height. Select Choose from Project, then select your known point.
Shooting check shots
Make sure your RS3 rover is receiving corrections and has a fix. On the survey screen, average each shot for 5 - 15 seconds. Turn off tilt compensation and level your rod to get the most accurate check shots from the equipment. Use high contrast points for your check shots such as GCP targets or high visibility painted targets. Once you have the check shots, set up the Matrice 300 with the L2 payload and plan your flight.
Configuring base and drone for RTK
Reconfigure the base to send RTK corrections to the drone. Change the base output from LoRa radio to Local NTRIP. On the drone controller, connect to the base’s Wi-Fi hotspot. Then enter the camera view on the drone to configure the RTK settings. Click the 3 dot icon in the top right to access the settings menu, then click the satellite icon to open the Precise Position settings. Select Custom Network RTK and input the base’s local NTRIP credentials
Flight planning and L2 settings
Go to the DJI Pilot home screen and select Flight Route to see the library of saved flights. Click the plus icon to Create a Route. The following example is an Area Route, but Waypoint Route and Linear Route are also available. Tap the screen to add points to define the area you want to map. Tap the checkmark to adjust your flight and payload parameters. In the Payload Settings select Penta Return and Repetitive. For a dense and accurate point cloud, fly at about 50 m altitude at 5 m/s or 164 ft at 12 mph. Input the Route Altitude and Speed also enable IMU Calibration. This example lacks large or sudden elevation changes, so the Side Overlap is set to 20% and the Forward Overlap is set to 70%. [If you have large elevation changes such as cliffs, steep valleys or a tower, raise the Side Overlap and fly parallel to those features to avoid missing chunks in your data. Upload and Start your mission.
Flying the mission - During flight there are multiple views available; the RGB camera, the live LiDAR collection, the first person view from the forward positioning camera, and the map view of your mission in progress. Displayed at the top of the screen are the flight mode, satellite count, RTK status, RC reception, battery levels, and the estimated remaining flight time for the batteries.
Preparing the mission folder for DJI Terra - Download your bases’ log for the mission by accessing it through a web browser. Remove the microSD card from the L2 payload and connect it to your PC. After the log is downloaded, unzip the file. Copy the data from the L2 to your computer. In your mission folder, copy the file name of the .IMU file and paste it to the observation file in the RINEX folder from your base. Changing the file extension from .230 to .OBS and put the file in the mission folder.
Download your check shots from Flow 360 by opening your project and selecting Export in the top bar. Export a Custom CSV file with Name, Easting, Northing, and Elevation selected.
Processing Options - In DJI Terra Start a New LiDAR Point Cloud mission. Browse and select the mission folder you prepped. Click the icon to the right of the Base Station Center Point Settings and input the same known point you used for your base, adding the height of the rod the receiver was on. Process your point cloud at 100% density. Under Point Cloud Processing, you have the option to Optimize Point Cloud Accuracy and Smooth Point Cloud as well as add parameters to automatically classify Ground Points, Generate a Digital Elevation Model, and add Contours. In the Advanced section, select the Coordinate System you would like the point cloud to be exported in.
Importing Checks - Click on Accuracy Control and Check in the Advanced section to import your check shots from your CSV file. Define the columns, then select the Coordinate Systems and Geoid settings used for your checks. Skip the first line that contains your headers, then select Import. Change the Type to Check Point as GCP will pull your elevations to the checks. Go back to the previous menu and select Start Processing.
Processing and Quality Checks - Visually check the accuracy of the LiDAR point cloud compared to your check points. You can check the hard numbers by clicking the Quality Report.
Additional measurement tools within DJI Terra - One of the additional tools available in DJI Terra: cross-section tool allows you to take slices of the data to see a profile view of the points and their values. Under Annotation and Measurement, you can also check individual coordinates, distances, areas, and volumes.
Everything you need to complete this mission is included in the E38 Complete LiDAR Biundle. It will enable you to collect survey grade LiDAR data and produce high quality deliverables. You can use Pix4Dsurvey or DJI Terra for your point cloud solution.
