How accurate is drone surveying really?

The honest answer is: it depends on what you mean by accuracy – and how you fly. You only get reliable figures when both are specified.

Two types of accuracy that are often confused

Relative accuracy describes how reliably measurements within the model are represented – lengths, areas and volumes. Absolute accuracy describes how correctly the model is positioned in the coordinate system. A model can be perfectly accurate internally and still be displaced by half a metre. The difference is explained under Precision vs. trueness.

Relative accuracy is sufficient for calculating the volume of a stockpile. As soon as results are incorporated into a cadastral system, a BIM model or a design, you need absolute accuracy.

The typical ranges

• Without correction, GNSS only: Positional accuracy in the metre range. Useful for overviews, but not for surveying.
• With ground control points: Depending on the number, distribution and surveying accuracy, in the range of a few centimetres – still the reference method.
• With RTK: Also in the centimetre range, without having to place ground control points. A continuous RTK Fix throughout the flight is a prerequisite.

In practice, vertical accuracy is lower than horizontal accuracy – if reliable elevation data is required, you should also survey additional check points when using RTK.

The hard upper limit

No method can produce a result that is more accurate than the ground sampling distance. If you fly at 3 cm/px, you will not get millimetre accuracy. You control the GSD through the flight altitude – flying lower means more images, longer flight times and greater processing effort.

What undermines accuracy in practice

Insufficient image overlap, too few or poorly distributed ground control points, low-texture surfaces such as snow or fresh asphalt, changing light conditions during the flight, and RTK dropping to Float intermittently. The sensor is rarely the problem – the workflow is.

Our advice: For your specific task, ask for an accuracy specification linked to a verification method. A figure in a brochure without check points is a marketing promise, not proof.

Not sure which option to choose? We provide manufacturer-independent advice – book an appointment.