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The Use of Drones in Land Surveying

You may have seen drones used for movie shoots, weddings, or other events. But nowadays, drones can do much more than that.

A lot of times when you say this, it’s usually theoretical or an idea that is still in the works, but what I’ll show you today is the hands-on experience of how drones are helpful in land surveying and GIS.

And if you are in the land surveying field and are still on the fence about how drones can help you, this is a must-read.

But briefly, how can you use drones in a land survey?

Drones replace kites, balloons, and airplanes as photogrammetry tools. They help collect georeferenced images, which can produce data like point clouds, orthomosaics, 3D models, thermal maps, etc., which have applications in industries like construction and agriculture.

But before we discuss how you can use them, let’s briefly discuss the history of aerial photography.

A Brief History of Aerial Photography/Survey

Aerial survey plays a crucial role in land survey, construction, archeology, and many other industries since it helps collect real-time geomatics data. However, it is not a new technology.

It has been around for more than a century and was first pioneered in the 1800s by Journalist and photographer Nadar (Gaspard-Félix Tournachon).

He was one of the first people to record an aerial view of Paris, and the idea quickly became popular worldwide.

Other notable pioneers include E.D. Archibald, a British Meteorologist, who used a kite fitted with a camera, and Alfred Maul, a German Engineer who sent a rocket with a camera into the air and let it take photographs as it descended on a parachute.

Aerial survey grew tremendously in the 19th and 20th centuries, especially during World War I and World War II, when aerial maps were used for reconnaissance.

Much of this success can also be attributed to the advancement in camera technology.

After the wars, aerial imagery entered the consumer world, where it was used for construction and research projects. Advancement in this technology post-war also resulted from man’s interest in traveling to space.

The Introduction of Drones

Just like with aerial imagery, the use of unmanned aircraft had been in the works for years. But by the end of the 20th century, drones had become more commonplace as traditional methods like kites and balloons were phased out.

However, drones or UAVs were used mainly by the military until they entered the consumer world at the onset of the 21st century. They have been revolutionizing a wide range of sectors since then.

How Drones Are Used In Land Survey and Mapping

While you could get an aerial view of an area or object from a satellite image, drones provide a more up-to-date, higher-resolution image which can then be used for further analysis.

For instance, images taken from a drone can be used when conducting volumetric calculations, crop health analysis, or infrastructure management.

Drones can also carry LiDAR sensors, thermal cameras, and RTKs, all of which enhance the accuracy of the data collected, providing even more insights to the end user.

How Do Drones Collect Data?

The images collected using a drone aren’t just simple images. They have a spatial phenomenon (longitude, latitude, and elevation) which makes them even more helpful for land surveys.

As already mentioned, you can also attach other payloads to collect a wide range of data in a single flight.

When compared to traditional surveying, drones are convenient, cheaper, and take less time since they can cover vast areas within a short time.

They are also safer since you don’t have to send a person up there, and they make it easier to collect data in inaccessible areas.

Since you don’t need complex drone maneuvers like in drone videography, it’s possible to input a flight plan where a drone will autonomously fly and collect the data.

Also, thanks to software like DroneDeploy and Pix4D, you can automate data collection, from flight planning to collecting the data.

Which Drones Are Used For Land Survey?

While you could collect aerial images with any drone, a drone that can fly following waypoints and carry extra payloads would be more suitable.

A drone’s GPS is not always accurate, so you may need to add an RTK or PPK payload.

And as mentioned earlier, thermal and LiDAR sensors may also come as third-party payloads.

You can use two types of drones:

  1. Fixed-wing
  2. Multi-rotor

Multi-rotors are the easiest to fly, but their batteries don’t last that long, so they are only ideal when surveying smaller areas.

When surveying several acres of land, fixed-wing drones are the best since they conserve energy, fly for a longer period, and have a higher payload capacity.

What Outputs Can You Get From A Drone Survey?

The outputs you get depend on the type of survey you are carrying out or the type of sensors you will use.

Below are the most common outputs you can expect to get.

2D Orthomosaics

2D orthomosaics involve taking several photographs of an area and then stitching them together to form one layout. Since it’s a 2D representation, it will be on an XY axis and will primarily be used to measure distances.

3D Orthomosaic Maps and Models

These are almost similar to 2D orthomosaics. The only difference is they have elevation data.

When you need to conduct volumetric calculations or other types of analysis on a construction project, this is the output to look forward to.

3D models are a more detailed representation that will help with the analysis.

Thermal Maps

Sometimes, the information you need may not be easily visible in the visible spectrum.

As such, you will need a thermal sensor that uses infrared to sense the heat emitted from an object, making it easier to identify the objects you couldn’t identify using visible light.

Such surveys are useful in agriculture, military operations, pipeline inspections, and cities.

LiDAR Point Cloud

LiDAR is an advanced data collection method that sends a laser to the area of interest and calculates the time the laser takes and how it’s reflected.

A LiDAR sensor is attached to the drone, and after post-processing, a LiDAR point-cloud map of the area is produced.

Multi-Spectral Maps

Multi-Spectral sensors collect data in a wide range of wavelengths, including those not visible to the human eye.

A multi-spectral map can give more information than a standard sensor, making them useful in construction, inspection, and precision agriculture.

Sample Drone Survey Project

Now that you know how UAVs are useful in land surveys, below is a sample project completed using a drone in my local area.

About The Project

This was a general aerial survey of a dam. It took less than an hour to fly the drone, collect the points, and conduct post-processing of the dam.

Preparation and Tools Needed

For this project, the following tools and preparation measures were implemented.

  • Phantom 4 Pro V2.0
  • Permissions to fly
  • Pix4D mapping software
  • Hand-held GPS or RTK
  • KML file of the dam

The Data Collection Process

Below is how you go about collecting data using a drone.

  1. First, you get the KML file which you can download from Google Earth Pro.
  1. Load this KML file in the Pix4D mobile app and use it to create a flight plan.

    Pix4D makes this process relatively easy. As you can see below, you, select your drone, select the type of mission, load your kml file, and adjust parameters like flight altitude, overlap, and flight patterns.
Select a drone
Select the mission
Load the KML to guide you on the area to execute the mission
Download the images
  1. Once everything is okay, set ground control points (GCPs) on the terrain you want to survey.

    You do this because the Phantom 4 Pro V2.0 lacks an RTK. So, since a drone’s GPS is not always accurate, GCPs help enhance the accuracy.

    If you use the Phantom 4 RTK drone, then you may not need to use GCPs.
  1. Check if the flight plan is okay, conduct a pre-flight check on the drone, and start the data capture.

    The whole process is automated, so data collection will only take a few minutes for a small region.

Post Processing

Below is how you can process the data from the drone:

  1. After data capture, Pix4D allows you to upload it to the Pix4D cloud for further processing.
  1. Create a new project on Pix4D Mapper.
  1. Add the drone images by clicking on Add Directories, which allows you to add the whole folder.

    But you can also use the Add Images option to add specific images.
  1. Specify the parameters like the coordinate system, Geolocation and Orientation, and the Selected Camera Model.

    But since Pix4D already has the Phantom 4 Parameters, you don’t have to set them.
  1. Select the output you want, which could be 3D maps, Multi-Spectral, or Thermal maps.

    It’s important to note that when setting the flight plan, you need to create a margin or an allowance by mapping slightly outside the area of interest to ensure sufficient overlap.

    But when it comes to post-processing, only highlight the area of interest.
  1. Next, select processing options for all the outputs: Point Cloud and Mesh, DSM, and Orthomosaics.
  1. There are three processing steps:
    a. Initial Processing
    b. Point Cloud and Mesh
    c. DSM and Orthomosaics.

    Remember the GCPs we took with a GPS or RTK? You should add them to the workflow after the initial processing.

    So, after setting the processing parameters, uncheck processes 2 and 3 and leave the Initial Processing checked.

    Then click Start. The output you get from this is a point cloud as you can see below.
Result After Initial Processing
  1. After initial processing, extract your GCPs and convert them to CSV format so you can upload them to Pix4D Mapper by going to Project > GCP/MTP Manager.
  1. Make sure you assign some of the GCPs as checkpoints.
  1. The following process is to mark those GCPs on the Pix4D Mapper by clicking on the respective GCP, finding it on the image on the far right, and clicking to mark it. You only need to mark 2 or 3 and click on Automatic Mapping to mark all other images. Below is how that looks like;
The Marking
After Automatic Mapping
  1. And you will have to do this for all the GCPs you have.
  1. After you are done marking the images, click Re-optimizing on the top menu.
  1. After that, check the two processing options you unchecked earlier and click Start.

    The production of the outputs is automated, so give it time, and you will get an email once everything is complete.
  1. Go to Mosaic Editor to view your outputs. You can export them and load them to ArcGIS or AutoCAD, depending on the nature of your project.

Outputs

After conducting the post-processing, below are the outputs for this specific project.

Georeferenced Orthomosaic
The Dam’s DSM (Digital Surface Model)
The Dam’s Topographic Map Developed Using ArcGIS
The Dam’s Profile Developed Using ArcGIS

Conclusion

A combination of drones and automated drone mapping software reduces what would have taken hours to complete to a few minutes and still provides accurate data.

And this is just a sneak peek. You can do a lot with them as long as you have the right tools and skillset.

Special thanks to:
Craig Cleave, MD at KENDRONE
George, Land Surveyor And Drone Pilot at KENDRONE
Chris, Drone Pilot at KENDRONE
Courtesy of KENDRONE Limited (link), a leading provider of commercial drone services and drone flight training institution in Kenya.