Using a drone to accurately map the progress of a construction site

Drones are generally used for taking photos and videos for creative purposes, but they are also a fantastic tool for creating accurate maps – which is exactly what a recent assignment called for. 

At the request of a landowner in the Midlands, we were tasked with checking up on the progress of a major project to improve access to a dual carriageway. The landowner wanted to make sure the construction work was being carried out within the agreed boundaries set out in the planning documents. Getting near-instant aerial imagery from us was seen as the ideal first step before potentially instructing a surveyor.

Pinpoint accuracy

A drone can take an aerial photograph of a construction site within seconds, but if accurate mapping is the goal then such a snapshot cannot be overlayed with an official map. To plot a precise map with a drone involves the use of multiple photographs stitched together to iron out any lens curvature and create a completely ​‘flat’ top-down view. 

For this task, we turned to a piece of software which automates the process and calculates a cross-hatched route over a chosen area before stitching the images together into a ​‘live’ map.

During the collection of the aerial imagery the drone flies itself within set parameters, but that does not mean our drone operator had it easy.

Busy airspace

This particular job fell within a busy regional airport’s FRZ, or Flight Restriction Zone. These are safe spaces around the take-off and approach areas of a runway and are out of bounds to the recreational drone flyer. However, licensed operators like Fortitude can apply to air-traffic control and seek permission for specific flights. 

In this instance, the airport could not have been more helpful. An initial phone call was followed by a request in writing, which was approved within 12 hours. Though as the permission warned, ​“aircraft will be in the area…it is your responsibility to ensure you remain clear of them!” and vigilance was key throughout our hour-long flight window. 

Despite the presence of commercial and light aircraft within the wider area, our three separate mapping flights passed without incident.

Further challenges

Flying over a construction site next to a busy dual carriageway presents other risks associated with operating a drone above people. Under the terms of our Civil Aviation Authority certification, drone operators cannot fly within 50m of people who have not been briefed about the flight, and that includes drivers and passengers in their cars, so we had to keep our distance from the busy road. 

If you are able to brief people about your presence and the potential safety implications, you are permitted to fly safely above them, which, having liaised with the site manager, is what we did to allow us to fly over small parts of the construction site and the workers beneath. 

The finished result

The software we use forms a low-resolution live view of the map as it is being created, overlayed with a GPS-tracked satellite map, which is handy for getting a rough idea of your progress during flight, but our the finished map we sent to the client still needed some fettling once the flying finished. 

As many as 120 high-resolution images were stitched together for each section of the construction site to form a single large and detailed image which could be overlayed first with mapping software and then with the map used in the council’s planning documents.

Aligning all three layers took precision and patience, but eventually revealed the construction work was proceeding without alarm. For our client, who received our detailed imagery the same day, this offered reassurance and peace of mind without recourse to an expensive ground-based surveyor. 

Get in touch

If you would like to discuss how drone services could help you please get in touch here.