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LiDAR capture and initial post processing

General overview of LiDAR data collection and processing

If you need to laser scan a large area, a powerful LiDAR drone may be the best solution. 

Here you can find a general idea of how the process of creation of a point cloud works, from flight planning to initial post-processing. For such a project you will need the following equipment and software:


  • UAV with LiDAR (for large-scale scans we recommend fixed-wing drones, such as FIXAR 007 with Topodrone 200+ LiDAR)

  • Ground station with software to create flight missions and control a drone (FIXAR XGroundControl Software)

  • Ground GNSS receiver (Base station, such as Emlid REACH RS2+)

  • LiDAR post-processing software (Since we are using Topodrone LiDAR 200+ LiDAR in this example, we will use Topodrone Post Processing Software)


Once all the equipment is ready, you can start creating the mission in your ground control software. Make sure your flight mission covers the whole area of interest with a buffer area and recommended overlaps between passes and at a recommended altitude. The mission should include a calibration “eight-figure” for LiDAR.


It is very important to choose the correct ground speed, altitude, and overlap parameters, as they will affect point cloud density and the overall efficiency of the survey. To keep altitude similar during LiDAR scanning we recommend using terrain-following flight mode when available.


After preparing your flight plan you can set up a base station. One of the ways to set up a ground station is over a known point. Keep in mind that it will take some time to get a satellite fix. The ground station will record navigation satellite data and create corrections.


When everything is ready for data collection load the flight plan into the UAV and start the mission. During the flight, the onboard LiDAR shoots laser beams hundreds of thousands of times per second and records a direction relative to the LiDAR and the distance to various objects and surfaces that were hit. For each measurement, the position of the LiDAR is recorded through GNSS data and angles through an inbuilt device inertial system.


Unfortunately, it is impossible to achieve very high precision for a moving object with GNS, and this is why we need the base station with a known location to create corrections. The innertial measurements unit (IMU) is also not absolutely precise as well and the correction for measured angles is generated during the post-processing


Once the mission is complete retrieve the data from the LiDAR and the base station.


You will need the following files

  • .imr - inertial system data from the LiDAR

  • .pcap - raw point cloud from LiDAR

  • .ubx - GNSS data from the LiDAR

  • .rnx - RINEX file from a base station


Now it is time for initial post-processing. First, you need to apply the corrections created by the base station to the flight pass of the LiDAR. Open Topodrone cloud-based software and select a LiDAR Post Processing tab.

TOPODRONE LiDAR Post Processing software
TOPODRONE LiDAR Post Processing software

Here you will need to upload the drone GNSS file (.ubx) and the drone inertial navigation file (.imu), select your drone model, or select antenna offsets if your drone model is not listed. And finally, upload the RINEX file from the base station (.rnx). In case you are missing .rnx file it is possible to use a Virtual Rinex file from the nearest base station, though in most cases it will lead to a lower precision.


After hitting Start the data will be uploaded to the Topodrone cloud server, make sure you have a reliable internet connection during this step. Corrections will be applied to the drone path and the new drone trajectory file will be generated.


The new trajectory file will be saved to your computer and the color-coded track will display in the map window. 

The green color indicates that the trajectory was computed with a Fixed solution, the yellow color indicates that the trajectory was calculated with a Float solution, and the red color indicates that the trajectory was calculated with a Single solution.

UAV trajectory with after corrections
UAV trajectory with after corrections

The new trajectory .pos file will be saved in the pre-selected folder.

 

Now you can generate a point cloud. Select the Cloud Generation tab and upload the LiDAR file and the just-generated track file.

Select the right coordinate system - typically the coordinate system depends on the particular location and is often provided by a customer.

You can trim the trajectory track and remove the unneeded areas.

TOPODRONE Cloud Generation Software
TOPODRONE Cloud Generation Software

At this time you can generate IMU calibration angles by selecting a small area with two parallel tracks and selecting strip alignment without cloud generation. For better results select an area with various vertical surfaces - preferably with few buildings. Click the Start button and the Topodrone Software will generate Roll, Pitch, and Heading  IMU calibration angles.

Finally, trim the trajectory that will be used in the cloud generation and start the processing.


Generation of a LiDAR cloud
Generation of a LiDAR cloud

The software will generate a .laz file - your initial cloud point is ready. The .laz file is a compressed .las file. 


Now this cloud can be processed in other software, such as LiDAR 360 to classify cloud points, verify accuracy, and more.


3D point cloud collected with FIXAR 007 drone and Topodrone 200+ scanner and software can achieve up to 2-3 cm accuracy.


Drone case study Illustrations

We look forward to getting in touch with you to better understand your needs and requirements. We will then offer you a range of UAV solution options to choose from.

Thank you! We will be in touch soon.

CONTACT US

Sarasota, FL

(941) 400 9260

New York. NY

(914) 531 4981

info@customdronesolution.com

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Fixar 007 fixed-wing drone

Custom Drone Solution
- industrial UAV systems developer and FIXAR official dealer

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