A standalone GNSS receiver (single-point positioning) is affected by ionospheric, tropospheric, satellite clock, and orbit errors, and is usually only accurate to the meter level. The core idea of differential positioning is to use a base station with known coordinates (or a correction service) observing the same satellites to measure the common errors and remove them, allowing the rover to reach centimeter- or even millimeter-level accuracy. Depending on the correction method and real-time capability, common techniques include DGNSS, RTK, Network RTK, PPK, PPP, and PPP-RTK. The following explains the principles, differences, and how to choose. For the GNSS systems themselves and their error sources, see What Is GNSS? The Five Satellite Positioning Systems and How They Work.
Quick Comparison
| Technique | Correction method | Typical accuracy | Real-time / post-processed | Base-station requirement |
|---|---|---|---|---|
| DGNSS | Pseudorange differential | Sub-meter to meter | Real-time | Single base / wide-area service |
| RTK | Carrier-phase differential | Centimeter | Real-time | Nearby single base |
| Network RTK | Networked carrier phase | Centimeter | Real-time | CORS network (e.g. e-GNSS) |
| PPK | Carrier-phase differential | Centimeter | Post-processed | Base station (post solve) |
| PPP | Precise ephemeris + models | Centimeter to decimeter | Real-time / post-processed | No own base needed |
| PPP-RTK | PPP + regional corrections | Centimeter | Real-time | Regional correction service |
How Each Technique Works
DGNSS (Differential GNSS)
A base station measures the pseudorange errors of each satellite and broadcasts corrections to nearby rovers to remove them. Simple and highly compatible, it reaches sub-meter to meter-level accuracy, suiting navigation and GIS data collection that do not require centimeter precision.
RTK (Real-Time Kinematic)
RTK differences the carrier-phase observations and resolves the integer ambiguity in real time to reach centimeter-level accuracy. It needs a nearby base station to transmit corrections in real time over radio or network; accuracy degrades as the baseline lengthens. It is the most common method for engineering surveying and real-time monitoring.
Network RTK
A network of continuously operating reference stations (CORS) generates a regional correction model (such as a VRS — virtual reference station), so users obtain centimeter-level real-time positioning with only a network connection, without setting up their own base. Taiwan offers services such as e-GNSS from the National Land Surveying and Mapping Center.
PPK (Post-Processed Kinematic)
PPK uses carrier phase like RTK, but solves rover and base data together afterward, requiring no real-time communication link. It suits UAV aerial surveys, sites without stable communications, or scenarios demanding the highest solution quality, since processing can be redone in the office to improve reliability.
PPP (Precise Point Positioning)
PPP uses precise satellite ephemeris and clock products together with full error models to reach centimeter- to decimeter-level accuracy with a single receiver, requiring no own base station. Its advantages are global applicability and simple deployment; the drawback is a longer initial convergence time (minutes to tens of minutes).
PPP-RTK
PPP-RTK combines PPP’s base-free advantage with a regional correction service to shorten convergence time and reach near-RTK centimeter-level real-time accuracy. It is a rapidly developing direction in recent years.
How to Choose
Work through the following questions step by step:
- Need only sub-meter to meter-level navigation or mapping? → Choose DGNSS.
- Need centimeter-level real-time results, with on-site network or a nearby base? → Choose RTK; without your own base, use Network RTK.
- Can accept post-processing and want the highest quality (e.g. UAV surveys)? → Choose PPK.
- Working over a wide area where deploying a base is impractical, and can accept convergence time? → Choose PPP (or PPP-RTK for both real-time and base-free operation).
Long-term structural monitoring typically uses fixed GNSS RTK monitoring stations to safeguard structures and slopes with continuous, centimeter-level 3D displacement, and can integrate with InSAR and field sensor data.
FAQ
Q: What is the difference between RTK and PPK? Both use carrier-phase differential and have comparable accuracy; RTK solves in real time and needs a communication link, while PPK processes the data together afterward without a real-time link, and is common in UAV aerial surveys.
Q: Why does PPP not need a base station? PPP instead uses global precise ephemeris and clock products together with error models for correction, so a single receiver can reach high accuracy — at the cost of a longer initial convergence time.
Q: How accurate can differential positioning be? Carrier-phase methods (RTK/PPK/PPP-RTK) typically reach the centimeter level, with horizontal accuracy of 1–2 cm under good conditions; DGNSS is sub-meter to meter-level.
Not sure which differential positioning approach fits your monitoring or surveying task? Feel free to contact RST Ltd..