C-DRONE GUIDE · 25 JULY 2026
RTK or PPK drone: what centimetre accuracy is for and when to require it
"RTK drone survey, centimetre accuracy": the phrase now appears on most contractors' brochures, and in a growing number of specifications — sometimes wisely, sometimes by reflex. Because the accuracy of a photogrammetric survey is not just about having an RTK module on the drone: it depends on the georeferencing as a whole, the quality of the flight and the checks performed. Requiring RTK for a communication orthophoto is pointless; skipping it for an as-built network survey is a mistake. This guide explains without jargon what RTK and PPK are, what they really change, and how a client — local authority, project manager, industrial firm — should word its accuracy requirement in 2026.
Published on 25 July 2026, reviewed on 27 July 2026 — regulations in force as of July 2026.
RTK, PPK, GCP: three acronyms, one issue
A standard drone records each photo's position with its onboard GPS, accurate to a metre or two: the resulting point cloud is internally consistent but "floats" in space. Three techniques bring that float down to the centimetre. RTK (Real Time Kinematic): the drone receives corrections in flight from a GNSS base or a network (Centipede-RTK, the open collaborative network backed by INRAE, has made these corrections free across much of France), and each photo is positioned to a few centimetres at capture. PPK (Post-Processed Kinematic): same data, corrected after the flight — more robust when the radio link is uncertain, in steep terrain for instance. GCPs (ground control points): independently measured targets that anchor and above all check the survey.
The point commercial brochures omit: RTK and GCPs are not alternatives, they complement each other. A 2021 study published in Remote Sensing by Štroner, Urban, Seidl, Reindl and Brouček compared georeferencing strategies for an RTK drone survey without control points: horizontal positioning delivers as promised, but systematic elevation errors can remain, and the authors recommend keeping at least one control point to secure the vertical component (see the study on Google Scholar).
The missions that justify centimetre accuracy
Requiring centimetre accuracy is justified when the deliverables will be measured or compared. Topographic surveys feeding design work (profiles, setting-out, earthworks); stockpile and quarry volumes, where an elevation error multiplies across hectares; quantitative construction monitoring (earthworks progress between two visits); as-built network surveys before backfilling; deformation and erosion monitoring, as on dams and levees or the coastline, where campaigns months apart are compared.
Conversely, an aerial photo, a corporate video, a visual roof inspection or a communication orthophoto has no need for centimetres: requiring RTK there inflates the price with no benefit. In between, the municipal orthophoto depends on use: simple base map, or support for measurements?
How to word the requirement in a specification
Good practice is not to impose a technology ("RTK drone mandatory") but a controlled result: a target accuracy expressed in centimetres horizontally and vertically, a reference coordinate system, and above all an independent check — verification points measured outside the calibration set, with the observed deviations appended to the report. A serious contractor will choose the combination (RTK, PPK, number of GCPs) that hits the target on the terrain at hand; that choice belongs to their method, not to the specification.
Two simple questions reveal how serious an offer is: "how do you verify the accuracy you claim?" (the answer must mention independent check points) and "what proof do you deliver?" (a table of deviations, not a software screenshot). These reflexes echo our guide on choosing a professional drone pilot: quality shows in the checks, not the hardware on display.
What RTK/PPK changes about the price in 2026
The extra cost of centimetre accuracy comes from equipment, calibration time and quality control. Orders of magnitude observed in France in 2026:
| Configuration | Price impact (excl. VAT) |
|---|---|
| Standard survey (native GPS, no control) | baseline — see our per-service guides |
| RTK/PPK option (equipped drone, network corrections) | +10 to 25% on the survey |
| GNSS-measured control and verification points | +€200 to €600 depending on number and access |
| Accuracy control report (deviations on independent points) | included to +€300 depending on contractor |
| Connection by licensed surveyor (regulatory value) | quoted separately |
On a photogrammetric survey billed at €1,500, the full centimetre requirement thus typically adds €300 to €600 — negligible if the deliverables size actual works, superfluous if they end up as meeting material. To put these amounts in context, see how much a drone service costs and our 3D photogrammetry guide.
Frequently asked questions about RTK and PPK
Does an RTK drone remove the need for any ground point? Horizontally, often; vertically, both the literature and field practice recommend keeping at least one control point plus independent verification points.
RTK or PPK, which to choose? The result is equivalent; PPK is more robust where the correction link is poor (valleys, dead zones). It is a method choice that belongs to the contractor.
Does centimetre accuracy apply to vegetation heights? No: it qualifies the positioning of measurable points. Over vegetation, photogrammetry measures the top of the canopy, not the ground — that is LiDAR territory.
What is a "centimetre accuracy" claim worth without a control report? Nothing verifiable: demand measured deviations on independent verification points — the only serious evidence.