PPK vs RTK vs DGPS vs PPP: GNSS correction methods compared
Key takeaways
- RTK and PPK both resolve carrier-phase ambiguities against a base and reach centimetre accuracy; the difference is when the corrections are applied.
- RTK needs a continuous correction link; PPK needs only raw data logged at both receivers and a processing step.
- DGPS and DGNSS use code measurements and typically deliver sub-metre to metre-level accuracy.
- PPP needs no local base but typically takes from several minutes to half an hour or more to converge to decimetre or centimetre level.
- Stakeout and machine control need RTK; drone mapping and long remote baselines often favour PPK.
PPK vs RTK: what is the difference?
In PPK vs RTK, the measurement principle is the same and the timing is different. Real-time kinematic (RTK) sends corrections from a base station to the rover during the survey, so the rover knows its centimetre position instantly. Post-processed kinematic (PPK) logs raw satellite observations at base and rover and combines them in software after the fieldwork.
Both methods measure the carrier phase of satellite signals and resolve the integer number of wavelengths (ambiguities) between the receivers. Once ambiguities are fixed, both typically give about 1 cm + 1 ppm horizontally and 1.5–2 cm + 1 ppm vertically over short baselines. Our introduction to RTK GPS covers the basic principle.
The practical difference is the link. An RTK system depends on radio or mobile data throughout the job; PPK does not, but you only know the quality of the result after processing.
What are the main GNSS correction methods?
There are four main families of GNSS correction: code-based differential (DGPS/DGNSS), real-time carrier-phase (RTK and network RTK), post-processed carrier-phase (PPK and static), and precise point positioning (PPP).
| Method | Measurements used | Base needed | Typical accuracy (H) | Time to result |
|---|---|---|---|---|
| Standalone GNSS | Code | No | About 1–5 m | Instant |
| DGPS / DGNSS, SBAS | Code, differential | Reference station or SBAS | About 0.3–1 m (SBAS often around 1 m) | Instant |
| RTK / network RTK | Carrier phase | Own base or CORS network | About 1–2 cm | Seconds to fix |
| PPK | Carrier phase, logged | Own base or CORS data | About 1–2 cm | After processing |
| Static post-processing | Carrier phase, long sessions | Own base or CORS data | Millimetres to about 5 mm | Hours of logging plus processing |
| PPP | Carrier phase and code, precise orbits and clocks | No local base | Decimetre to a few centimetres | Minutes to tens of minutes of convergence |
Accuracy figures are typical for good conditions and multi-band receivers; obstruction, multipath and long baselines reduce them. To estimate RTK error for a given baseline, try our RTK accuracy calculator.
What is DGPS, and what is DGNSS vs GNSS?
DGPS (differential GPS) improves standalone positions by applying code corrections calculated at a reference station of known position; when it uses several constellations it is called DGNSS. The difference in DGNSS vs GNSS is that the differential version removes most satellite orbit, clock and atmospheric errors common to the reference and the user.
DGNSS accuracy is typically sub-metre to about a metre, depending on distance to the reference, receiver quality and the correction source. Sources include satellite-based augmentation systems (SBAS) such as WAAS and EGNOS, local reference stations, and some marine radio beacon services, although several national beacon networks have been discontinued.
DGNSS is enough for GIS asset inventories at metre level, vessel navigation and vehicle tracking. It is not suitable for boundary, construction or engineering survey work, where centimetre accuracy is required.
How does an RTK system work and what are its limits?
An RTK system works by streaming carrier-phase observations from a base on a known point to the rover, usually in RTCM 3 format, so the rover can compute a fixed centimetre solution every second or faster.
Corrections reach the rover in two main ways:
- UHF radio from your own base: independent of mobile coverage, typically a few kilometres with internal radios and further with an external high-power radio and mast antenna.
- Network RTK from CORS: rtk correction services deliver data over the internet using NTRIP, as described in our NTRIP and CORS guide.
The limits are distance and link reliability. Accuracy degrades by roughly 1 mm per kilometre of baseline, and ambiguity resolution becomes harder beyond about 10–20 km from a single base. When the radio or data link drops, the rover falls back to float or autonomous positions until the link returns.
How does PPK work step by step?
PPK works by logging raw GNSS observations at a base and a rover at the same time, then processing the two files together to compute a centimetre-level trajectory or point positions.
- Set up the base on a known point, or plan to use data from a nearby CORS station at a suitable logging rate.
- Log raw data on both receivers at the same rate, often 1 Hz for ground work and 5–10 Hz or more for drones and vehicles.
- Record metadata: antenna heights, antenna types and base coordinates.
- Collect the rover data, with event marks for camera triggers or point occupations.
- Convert files to a common format such as RINEX if needed.
- Process forwards and backwards in time; this combined solution is one reason PPK often fixes more epochs than RTK.
- Check quality: fix percentage, residuals and check points, before delivering results.
Because nothing depends on a live link, PPK keeps working through radio shadows and areas with no mobile signal.
What is PPP, and how does it compare with RTK and PPK?
Precise point positioning (PPP) is a correction method that uses precise satellite orbit and clock data from a global service instead of a local base, so a single receiver can reach decimetre or centimetre accuracy anywhere.
The trade-off is convergence time. Classic PPP typically needs from about 15 to 30 minutes or more to reach decimetre-level accuracy, and longer for a few centimetres, because the receiver must estimate atmospheric delays and ambiguities on its own. PPP-RTK services add regional atmospheric corrections to shorten this to minutes or less. Free services include the Galileo High Accuracy Service and BeiDou PPP-B2b in their service areas; commercial services are delivered by satellite L-band or internet.
PPP suits offshore work, remote mapping, agriculture in areas without CORS and geodetic control processing. It is rarely used for stakeout because of convergence and re-convergence after signal loss.
Should you use a PPK drone or an RTK drone?
For mapping drones, PPK is usually the more robust choice and RTK is the more convenient one; many current survey drones support both.
| Factor | RTK drone | PPK drone |
|---|---|---|
| Correction link in flight | Required | Not required |
| Results on landing | Geotags already corrected | Needs processing step |
| Link dropouts | Lose fix for affected images | No effect |
| Remote sites without mobile data | Needs own base radio | Works with a logging base |
| Ground control points | Fewer needed; keep check points | Fewer needed; keep check points |
A PPK drone needs accurate camera event timing and a base logging at a suitable rate. In both cases, keep independent check points on the ground. Our guide to survey drones and UAV mapping covers flight planning and accuracy in more depth.
What are common mistakes with RTK and PPK corrections?
Most correction errors come from the base, not the satellites: a wrong base coordinate, antenna height or datum shifts every rover point by the same amount, whichever method you use.
- Wrong base position or datum: a base set on an averaged autonomous position can be several metres off. Use known control, or post-process the base against CORS, and confirm the network frame matches the project.
- Antenna height and type errors: record the measurement method and antenna model at base and rover; in PPK, missing metadata is a frequent cause of height errors.
- Accepting float solutions: float results can be decimetres off. Set the controller or processing software to keep fixed epochs only.
- Mismatched logging rates in PPK: a 30-second CORS file cannot support a 5 Hz drone trajectory well; check rates before the flight.
- No independent checks: measure a known point at the start and end of each RTK session, and keep check points in PPK projects.
Our engineers also recommend saving base and rover settings as named profiles, so the same correction format, radio channel and coordinate system are used on every day of a project.
Which GNSS correction method should you choose?
Choose RTK when you need centimetre results immediately, PPK when the link is unreliable or the platform moves fast, DGNSS for metre-level GIS, and PPP when no base or network is available.
- Stakeout, construction layout, machine control: RTK or network RTK.
- Topographic and boundary surveys: RTK, with PPK or static as a backup in poor coverage.
- Drone photogrammetry and lidar: PPK or RTK, with check points.
- Control networks: static post-processing.
- Remote or offshore areas: PPP, or your own base with long-range radio.
Integrators building their own products around an RTK module or GPS board can read our guide to GNSS OEM module integration.
For field crews, our E1 GNSS RTK receiver works as radio base, radio rover or CORS/NTRIP rover with a typical 5 km internal radio range in open terrain. The lighter E1 Lite GNSS receiver weighs about 870 g, with an internal radio rated at 3–15 km depending on environment. Where you need a longer radio link from your own base, our external UHF radio transmits at 5 W or 25 W on 410–470 MHz, reaching roughly 20–25 km in open, elevated terrain. If you plan to post-process, tell us your logging requirements when you request a quote and our engineers will confirm the right configuration.
Frequently asked questions
Is PPK more accurate than RTK?
Not inherently. With the same receivers, base and conditions, PPK and RTK give similar accuracy, typically 1–2 cm horizontally. PPK can deliver more fixed epochs because it processes data forwards and backwards and is unaffected by link dropouts, so the overall result is often more complete and consistent, especially on drones and fast-moving platforms.
What is DGNSS accuracy?
DGNSS accuracy is typically sub-metre to about one metre horizontally, depending on the correction source, distance to the reference station and receiver quality. SBAS corrections often give around one metre. That makes DGNSS suitable for metre-level GIS mapping, marine navigation and vehicle guidance, but not for surveying tasks that need centimetre accuracy.
Can I do PPK without my own base station?
Often yes. Many CORS networks and national geodetic agencies publish raw base data that you can download for post-processing. Check that the station is close enough, ideally within about 10–20 km, that it logs at a rate suitable for your survey, and that its coordinates are in the datum your project uses. Otherwise, log your own base.
How long does PPP take to converge?
Classic PPP typically takes about 15 to 30 minutes or more to converge to decimetre accuracy, and longer for a few centimetres. Convergence restarts after a major loss of signal. PPP-RTK services with regional atmospheric corrections can reduce this to a few minutes or less, but availability depends on the service area and the receiver supporting it.
What are RTK correction services?
RTK correction services are networks of continuously operating reference stations that stream real-time corrections to rovers over the internet, usually using the NTRIP protocol. They may be run by government agencies, universities or commercial providers, and they remove the need to set up your own base. You need a subscription or account and reliable mobile data on site.
Is RTK or PPK better for drones?
Both work well. RTK gives corrected image positions immediately on landing but depends on a continuous link during flight. PPK needs a processing step but tolerates link dropouts and remote sites, which is why many survey teams prefer it for mapping. With either method, measure independent ground check points to verify the final accuracy.
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