Ground control strategy should reflect the quality of the aircraft’s positioning system, the site size and geometry, and how much confidence the final deliverable needs to carry.
Strong RTK and PPK systems can reduce the amount of full ground control needed, especially on cleaner sites. Older aircraft, weaker GNSS workflows, and more difficult sites usually require a more conservative control plan.
For Non-RTK drones
Since non-RTK drones photo geolocations are not very relatively accurate to one another, the real world and relative integrity of the model is highly dependent on the quantity and distribution of the GCPs to tie it down. In practice, this means that there needs to be GCP representation in every few photos to ensure the model can be pinned to real world coordinates without straying.
Non-RTK Best Practices:
- Ensure control outlines the perimeter of your area of interest and has an even distribution throughout. Any part of your model not pinned by a GCP can "wander"
- 5 GCPs minimum per site
| Altitude | Spacing |
|---|---|
| 150' | 500-600' |
| 200' | 600'-700' |
| 300' | 800' |
| 400' | 1000' |
For RTK Enabled Drones
Since RTK enabled drones photo geolocations are generally very relatively accurate to one another right out of the drone, GCP requirements are more relaxed. GCPs are still needed to verify project accuracy, but instead of being required to make small unique adjustments to data across many photos with varying geolocation variances, global offsets can be applied to the entire photo set or model to align with the GCPs. And because of this, we don't need as many of them, or as even of a distribution to get the same (or better) results.
RTK Best practices:
- Distribute GCPs throughout the site as able
- Minimum 3 GCPs (5 recommended)
- 1500' spacing between GCPs
Aerotas’ practical position: even when technology makes low-control workflows possible, flying a professional survey site with no ground data at all is not a good idea.
Aerotas also recommends taking a number of checkshots that you withhold and use to verify the final data with after product delivery. This practice gives you the validation data you need to have trust in the data.
GCP Visual Representation and Integrity
A perfect GCP layout can be rendered completely useless if the GCP's visual representation in the photos is ambiguous or if your targets move between measurement and flight. GCPs represent a highly accurate point, and thus should be represented by an unambiguous, highly visible spot in the photos, that doesnt' move.
Aerotas GCPs are designed to be highly visible, easy to deploy and secure, and biodegradable, but any highly contrasting checkerboard pattern no smaller than 12"x12" can work.
Common Ground Control Pitfalls
- Setting Control outside your flight area
- using ambiguous shapes where the measured point is not obvious
- Setting control in high traffic areas that are not fixed to the ground
- Setting control where a car might park
- Not setting enough control on both sides of a body of water when it splits the site in two.
- Setting control in a straight line without any other variation on linear projects.
Need help with your control layout? Create a new project in the Aerotas web app and request mission planning from My Projects.