Is a Drone Survey Accurate?

Aerial Inspection of flat roof by Drone Site Surveys
November 16, 2021

One of the questions that we get here from many customers is, how accurate is a drone survey? In terms of land surveying, accuracy can be key to everything you are looking for in your survey. Traditional surveying methods all require a lot of work and precision to ensure that accuracy across the project is achieved. This involves a lot of expensive time for surveyors, not to mention, the potential need for a lot of expensive equipment if your target is high in the air such as a roof. Deploying drones can help reduce your time on site and equipment hiring costs by surveying from the air.

Is Drone Survey Accuracy Important?

Absolutely! The whole task as a surveyor is to provide accurate readings of your project, both before during, and after. There are many reasons accuracy is key to everything. With planning applications, material costs and land borders all depend on accurate measurements. This is why the tools are expensive and the job time-consuming using traditional surveying methods.

However, drones are now fitted with so much technology that even from 200 feet (61meters) in the air your construction site can be mapped and every detail scanned.

So, Is a Drone Survey Accurate?

In short yes! But we should explain how accurate and how this accuracy is achieved. 1st of all, the accuracy does depend on the drone used and the supporting equipment you have on-site. The accuracy of a drone survey can be narrowed down to +- 1cm. However, this does depend on your drone, equipment, and processing software. For us here at Drone Site Surveys we used drones particularly created for surveying.

How is the Accuracy Achieved

The technology a drone is fitted with (depending on your drone) will have GPS data. This is so that flying is completed in an extremely safe manner. Drones such as the DJI range also use their software to ensure where you intend to take off is permitted and legal. This data is embedded into each photograph you take along with information such as height and camera angle, to help you understand exactly where the photo was taken and what you are looking at.

The GPS equipment inside the drone isn’t particularly accurate with some drones reporting up to +-10m accuracy. This is a long way off the 1cm we have cited further up the page. The reason is, the drone’s GPS data needs to be calibrated and calculated using an extra piece of equipment called a ground control point. This ground control point uses extra GPS data to find an exact location accurate to +-1cm and the drone then calculates the distance from this control point. This leads the way to the data captured having the precise accuracy that a surveyor may need to complete their task.

What Happens With the Data?

Although the data is stored in the photographs, it’s pretty useless unless you combine it with photogrammetry software. This will take all of your images and scan the data in, from every single one of them. Then the software builds a map of the area in 2D or 3D depending on your requirements so that you can see your project on the computer screen from every single angle. This is called a model or a map of your project.

Once the map is created, your software will allow you to calculate measurements across the map with an accuracy of +-1cm. Not only that, as it’s stored on your computer, you can come back time and time again to measure something different. The only time you would need to go back out to the site and scan again with the drone is if something has changed such as a new building/structure has been added.

Although this whole process of measuring with drones sounds complex, in reality, for you as a surveyor it’s straightforward. If you are hiring a drone survey company, all you need to do is tell them the area you’d like to scan. Their fully qualified pilot will then take the drone up and take all the images required in one day and process them in photogrammetry software such as Pix4D. Depending on your requirements, the drone surveyor will take the measurements you require from the software, or, they can give you access to the software online to take your own. This whole process can be done extremely quickly with small sites being available to measure on the same day. This massively reduces the cost of your surveying and measuring. If you are a surveyor and you’re not using drones to help your site operations, then you really should be asking yourself why as they do help you work smarter.

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