What are GCPs and when do you need them?
GCPs, ground control points, show up in every drone survey quote. Sometimes they are essential, sometimes you are paying for something you do not need. Understanding the difference saves money — and prevents a survey that ends up metres off.
What is a GCP, really?
A ground control point is a clearly marked point on the ground — a painted target or a physical marker — whose exact coordinates (for example in Lambert 72 and TAW) have been surveyed. During processing the software uses those points to anchor the drone model to the real world. Without such an anchor the model "floats": the shape is right, but the absolute position and height can be well off.
Why they make the difference
Without control, a drone model can deviate by metres from the real coordinates. You cannot see it from the image — it looks perfect — but it shows up the moment you lay the data over a surveyor's plan or existing infrastructure. GCPs (or a good RTK solution) pull that deviation back to centimetres. How that flows through to the reliability of a measurement, read How accurate is a volume measurement?
When do you really need them?
- You need them if the data has to tie into a surveyor's plan, existing infrastructure or another dossier — in short, whenever absolute accuracy counts.
- You need them for a dossier-grade, contestable measurement where the evidence must be solid.
- RTK alone can be enough for purely relative measurements, such as a volume where only the shape and relative heights count.
- In doubt? Then rather yes. Adding control points afterwards is impossible; the flight then has to be redone.
Common mistakes
- Working without control points and still claiming absolute accuracy.
- Too few or poorly spread points. A good spread (corners plus centre) matters more than many points in one spot.
- Thinking the nice picture guarantees it. Accuracy is not seen, it is measured.
Why with a drone (and why Droneview)?
With the right combination of RTK and control points, a drone flight delivers a model that is centimetre-correct and verifiable. Droneview operates EASA-certified with its own RTK base station. Have your own drone but no RTK or survey gear? Then we set and measure the points for you — see our GCP service.
Frequently asked questions
What is a ground control point (GCP)?
A clearly marked point on the ground whose exact coordinates are known. It acts as an anchor to tie the drone model to the real world.
When do I need GCPs?
Whenever you need absolute accuracy: tying into a surveyor's plan or existing infrastructure, or a dossier-grade measurement. For purely relative measurements such as a volume, RTK alone can sometimes be enough.
Does RTK replace GCPs?
RTK already gives strong absolute positioning, but GCPs remain the check and the proof. For critical or contestable dossiers it is best to use both.
Points needed for your mapping?
Tell us about your project — we advise honestly whether you need GCPs and set them if required.
Request a quote