Topographical Survey Drone Pilots

What this service involves

A topographical survey records the shape of the ground and everything fixed on it: levels, slopes, kerb lines, drainage covers, tree positions, buildings and boundaries. Flown from the air, it is a grid of overlapping images processed into a terrain model, from which contours and spot levels are drawn.

It is a measurement exercise rather than a photographic one, and it is normally commissioned to a standard somebody else has set. The specification usually names the accuracy required, the contour interval and the datum the levels must be tied to, and those decide how the flight is planned rather than the other way round.

Who hires drone pilots for this, and why

Architects and planning consultants, who need existing levels before a building can be designed onto a site, and who are usually working to a submission date set by a planning authority.

Civil and drainage engineers, for whom falls and levels across a site determine whether a scheme works at all.

Developers pricing a site, where cut and fill volumes derived from the terrain model change what the ground costs to build on.

Local authorities and highways teams recording an existing carriageway, footway or verge before works.

What to expect on the day

The specification is agreed before anything is flown, because it decides the ground control, the flying height and the processing. Control markers are placed and surveyed, the grid is flown, and features the camera cannot resolve or cannot see, such as inverts inside a manhole or ground beneath a canopy, are picked up on foot.

Deliverables are normally a drawing in a CAD format with levels and contours, a terrain model, and the orthomosaic behind them. Expect the drawing rather than the imagery to be the thing the design is worked from, and expect the surveyor signing it to be answerable for the levels on it.

Topographical Survey: frequently asked questions

Is an aerial topographical survey accepted for planning?

What a planning authority accepts is a drawing prepared to the standard it asks for, not a particular method of collecting the data. Aerial capture is one way of producing that drawing and is commonly combined with ground observation for detail the camera cannot see.

What accuracy should I ask for?

Ask the person who will use the drawing rather than the person flying. The engineer or architect designing from it will have a tolerance in mind, and stating it up front decides the ground control and the flying height. A survey flown without a stated tolerance cannot be checked against one afterwards.

Does the whole site need to be accessible?

The flight does not need access to every part of the site, but the ground control does, because the markers have to be placed and surveyed. Areas that cannot be reached on foot can still be flown, with the understanding that they are tied in less tightly than the rest.