Quick Answer
RTK (Real-Time Kinematic) provides centimetre-accurate positioning during flight using live correction data, while PPK (Post-Processed Kinematic) achieves the same accuracy by processing correction data after the flight. RTK is simpler and gives immediate results. PPK works in areas with no mobile signal and avoids mid-flight correction dropouts.
How RTK Works
RTK uses a base station at a known location to send correction signals to a rover receiver on the drone. The corrections are applied in real time, so the drone always knows its exact position during flight. This means your aerial photos are already geotagged with centimetre accuracy when you land. No post-processing is needed.
Corrections are delivered either via a radio link from your own base station or through an NTRIP service over mobile data. If the correction link drops mid-flight, the drone's position accuracy degrades until corrections resume. For detailed setup instructions, see our Emlid Reach base and rover guide.
How PPK Works
PPK records raw GNSS observations on the drone during flight, along with time-stamped camera trigger events. After landing, you process the raw data against correction data from a base station or NTRIP service. The processing software calculates the precise position of each photo after the fact.
Because PPK does not need a live correction link during flight, it works in remote areas with no mobile signal and is not affected by radio dropouts. The trade-off is that you must wait until after the flight to know your accuracy, and the post-processing step adds time to your workflow. The Reach UAV Mapping Kit supports both RTK and PPK, letting you choose per mission.
RTK vs PPK Comparison
| Feature | RTK | PPK |
|---|---|---|
| Correction timing | Real-time during flight | Processed after flight |
| Mobile data required | Yes (for NTRIP), or radio | No |
| Accuracy | 1-2cm | 1-2cm |
| Works in remote areas | Only with radio base | Yes |
| Workflow speed | Faster (no post-processing) | Slower (processing step) |
| Mid-flight dropout impact | Loses accuracy until restored | No impact |
| Ground control points needed | None or minimal | None or minimal |
When to Use RTK
RTK is the best choice when you have reliable mobile data or can set up a local base station with a radio link. It suits repeat surveys of the same site, construction monitoring, and any situation where you need immediate results. A receiver like the Emlid Reach RS4 works well as a base for RTK. You can verify your accuracy in the field before packing up, which avoids the risk of discovering a problem after you have left the site.
When to Use PPK
PPK shines in remote locations where mobile signal is unreliable or absent. It is also useful for large mapping jobs where radio range might not cover the entire area. The Reach RS4 Pro can serve as a PPK base, recording data for post-processing after the flight. PPK is more forgiving of brief satellite outages during flight because the post-processing software can bridge small gaps in the data.
Combining Both Approaches
Many mapping pilots run both RTK and PPK simultaneously. The drone gets real-time corrections for live quality control, and the raw data is also logged for PPK as a backup. If the RTK link drops at any point during flight, the PPK data fills in the gaps. This dual approach gives you the best of both worlds with minimal extra effort.
Accuracy Compared to Ground Control Points
Both RTK and PPK achieve similar accuracy to traditional ground control point surveys, typically within 1-3cm horizontal and 2-5cm vertical. For most mapping applications, this eliminates the need to place and survey ground control points manually, which saves significant time on large sites. For the highest accuracy requirements, a few strategically placed GCPs can supplement RTK or PPK for an extra layer of verification.
For more on adding GPS positioning to a drone build, see our GPS modules guide. Browse compatible receivers and mapping kits in the GPS navigation systems collection.