Drone surveying for construction: what you get and when to use it

Drone surveying has gone from novelty to routine on construction sites in a few years, mostly because it measures something a rover never could at a sensible cost: the whole surface of the site, every week. It has not replaced the surveyor, and it is not meant to. This guide says what a drone survey delivers, where it beats traditional methods and where it does not, the rules that apply, and how to decide between hiring it in and flying it yourself.

What a drone survey is

A drone flies the site in a grid, taking overlapping photos from a set height. Photogrammetry software matches points between the photos and works out the shape of the ground, and positioning from ground control, RTK or PPK ties it to real coordinates. (How aerial photogrammetry works.) Some drones carry a laser scanner (LiDAR) instead of, or as well as, a camera; the deliverables are much the same.

What you get

Where a drone beats a rover

• Surfaces. A rover measures points a person walks to; a drone measures the whole surface. On a 30 acre site that is a few hundred shots against a hundred million heights or more.
• Stockpiles and steep ground. Nobody climbs the pile or walks the face. (Measuring stockpiles.)
• Speed and repetition. A site flown in half an hour can be flown every week, which is what makes progress measurable. (Progress monitoring with drones.)
• The record. Each flight is a dated, measurable picture of the whole site, which settles arguments months later.

Where a rover or total station still wins

• Boundaries and legal surveys. Property lines, easements and anything recorded need a licensed surveyor and their instruments.
• Setting out. Putting a peg where the design says needs a point measured to millimetres, in real time, on the ground.
• Under cover. Under trees, inside buildings, under bridges: a camera cannot see the ground.
• A handful of precise points. Checking a few levels on a slab is quicker with a rover than a flight and its processing.

The rules

• To fly: in the United States, any commercial drone flight needs a pilot with an FAA remote pilot certificate (Part 107), and controlled airspace near airports needs an authorisation, usually granted in minutes through the FAA's automated system.
• To call it a survey: boundary and legal surveys must be done or signed by a licensed professional land surveyor in every state, and some state boards treat topographic maps produced for others as surveying. Mapping your own site for your own measurements is a different matter from selling maps as surveys; check your state board's position before doing the second.
• On site: the site's own permit to fly, the client's rules, and the people under the flight path.

How a drone survey is done

1. Plan: the boundary, the height for the ground resolution you need, the overlap, the airspace. (GSD calculator.)
2. Control: lay and measure ground control, or rely on RTK or PPK with a few checkpoints. (What each gives you.)
3. Fly: minutes to an hour, ideally in even light with the site still.
4. Process: photos into the orthomosaic and elevation models, from an hour to most of a day.
5. Check: read the checkpoints off the map and compare them with the surveyed values.
6. Measure and deliver: volumes, cut and fill, contours, and the files for CAD.

Hire it in, or fly it yourself?

For one or two surveys, hire a drone services company or a surveyor with a drone. Once a site is flown monthly, owning a mapping drone usually pays for itself inside a year, and the bigger benefit is timing: the drone is on site the morning the question comes up. (What each option costs.) Either way, the processing and the measuring can sit with you. Clarity takes the orthomosaic and terrain model from whoever flew the site and puts them in a browser for everyone who needs to measure (Studio), or processes your own photos into them (Enterprise).