Drone vs. manual survey vs. satellite
Which method delivers the most accurate roof area with the least time on site? Comparison, accuracy and a glossary of the key terms.
How accurate is a drone roof survey?
With correct image capture — nadir and oblique shots, 20–30 m above the ridge, at least 75 percent overlap — a drone roof survey achieves an area accuracy of a few centimetres. The decisive factors are overlap, ground sampling distance (GSD) and the number of images.
- Combine nadir and oblique shots: nadir for the surface, oblique for edges and eaves.
- Stay 20–30 m above the ridge — higher reduces resolution, lower needlessly increases the image count (guideline).
- Keep overlap at 75 percent or more so photogrammetry can reconstruct every point from several images.
- A smaller ground sampling distance (GSD) means finer detail — it depends on flight height and camera.
The figures above are professional guidelines for a well-planned capture; the actual accuracy depends on the roof, weather, camera and image quality.
Drone vs. manual survey vs. satellite
The three common methods compared directly by accuracy, time on site and whether a roof inspection is required.
| Method | Accuracy | Time on site | Inspection needed |
|---|---|---|---|
| Drone (photogrammetry) | a few centimetres | approx. 10–15 min | No |
| Manual survey | centimetres to decimetres, error-prone | 1–2 hours | Yes |
| Satellite / aerial imagery | coarse, imprecise for detailed areas | none (instantly available) | No |
Practical guideline values for drone roof surveying. The drone method avoids climbing onto the roof (occupational safety) while delivering the highest level of detail accuracy.
Roof surveying glossary
The key terms around photogrammetry and roof surveying — briefly explained.
- Nadir
- A vertical shot pointing straight down. Nadir images capture the roof surface with little distortion and are the basis for area calculation.
- GSD (Ground Sampling Distance)
- Ground resolution — the distance on the ground covered by one image pixel. A smaller GSD means finer detail; it decreases with lower flight height and higher camera resolution.
- Orthophoto
- A rectified, true-to-scale aerial image. Distances and areas can be measured directly and to scale in an orthophoto.
- Photogrammetry
- A method that computes a 3D model and precise measurements from many overlapping photos. The foundation of drone roof surveying.
- Ridge
- The topmost, horizontal edge of a pitched roof where two roof surfaces meet.
- Hip
- The outward-sloping edge where two roof surfaces meet around a corner (convex edge).
- Eave
- The lower, horizontal edge of the roof where rainwater runs off — usually with a gutter.
- Valley
- The inward-sloping edge where two roof surfaces form a channel (concave edge) in which water collects.
When is drone surveying worth it instead of a manual survey?
Drone surveying is worth it as soon as accuracy, occupational safety and time on site matter — that is, for almost any roof in solar, roofing and planning projects. It avoids climbing onto the roof, fully documents the current state and delivers a reusable 3D model instead of individual hand measurements.
Next step
How to measure a roof in Roofy
Draw a polygon, check the elevation map and set measurement lines — step by step.