How RTK & PPP Technologies Improve GNSS Receiver Accuracy
Eview GNSS Technology supplies high-precision GNSS receivers — all powered by Septentrio chipsets — that implement both RTK and PPP correction technologies. This guide explains how RTK and PPP work, their differences, and when to choose each for your application.
GNSS receivers determine position by processing signals from orbiting satellites. Without correction, standard GNSS accuracy ranges from 2 to 5 metres — insufficient for machine control, drone mapping, or geodetic surveying. RTK and PPP close this gap. This article explains how each technology works, their respective strengths, and how to choose the right approach.
What Limits Raw GNSS Accuracy?
Before exploring RTK and PPP, it helps to understand what degrades raw GNSS accuracy:
- Ionospheric delay: The ionosphere slows GNSS signals by amounts that vary with solar activity, time of day, and latitude. This is the single largest error source in civilian GNSS — up to 5 metres on a bad day.
- Tropospheric delay: Water vapour and air pressure slow signals near the horizon. Typically 0.1–0.5 metre error.
- Satellite clock errors: GNSS satellites carry atomic clocks accurate to ~1 nanosecond, but residual drift causes sub-metre errors.
- Satellite orbit errors: Broadcast ephemeris is accurate to ~1 metre; precise post-processed orbits achieve ~2 cm.
- Multipath: Signals reflected off buildings or terrain arrive at the receiver on a longer path, causing ranging errors of 0.1–1 metre.
RTK (Real-Time Kinematic) Explained
RTK is the dominant correction method for centimetre-level positioning in professional survey, UAV, agriculture, and construction applications. It works by comparing observations between a receiver at a known fixed location (the base station) and your mobile receiver (the rover).
The base station continuously transmits its GNSS observations via radio link or NTRIP internet connection. The rover receives these corrections and applies them in real time, cancelling out the ionospheric, tropospheric, and satellite errors that affect both receivers equally.
RTK accuracy: 1–2 cm horizontal, 2–3 cm vertical under normal conditions. Eview GNSS receivers powered by Septentrio mosaic chipsets achieve 1 cm + 1 ppm horizontal, 2 cm + 1 ppm vertical RTK accuracy.
How RTK Fix is Achieved
RTK relies on resolving the integer ambiguity in carrier phase measurements — the process of determining how many complete wavelengths of the satellite signal lie between the satellite and receiver. Once resolved (a “fixed” solution), centimetre accuracy becomes available.
Multi-frequency receivers (L1+L2+L5) resolve ambiguities much faster than single-frequency: typically under 10 seconds for Septentrio mosaic-series chipsets vs 5+ minutes for single-frequency. This is why Eview GNSS specifies only multi-frequency Septentrio receivers.
PPP (Precise Point Positioning) Explained
PPP achieves sub-decimetre to centimetre accuracy without a local base station. Instead of a nearby reference, PPP uses globally modelled corrections — precise satellite orbits and clock corrections broadcast by services such as SBAS, SSR (State Space Representation), or commercial providers (e.g. Trimble RTX, Fugro StarFire, TerraStar).
PPP accuracy: 3–10 cm horizontal after convergence. Convergence time is typically 15–30 minutes, though PPP-AR (ambiguity resolution) can reduce this to under 1 minute with multi-frequency receivers.
RTK vs PPP: Direct Comparison
| Feature | RTK | PPP |
|---|---|---|
| Accuracy | 1–2 cm | 3–10 cm (1–3 cm with PPP-AR) |
| Convergence time | <10 seconds (multi-freq) | 15–30 min (1 min with PPP-AR) |
| Base station required | Yes (local or CORS network) | No |
| Coverage | Typically <50 km from base | Global |
| Data link needed | Yes (radio or internet) | Yes (satellite or internet) |
| Best for | Survey, UAV, construction, agriculture | Remote areas, offshore, maritime |
| Cost of correction service | Free (CORS) to moderate (commercial) | Free (SBAS) to high (commercial) |
RTK vs PPK: What Is the Difference?
PPK (Post-Processed Kinematic) is a variant of RTK where the corrections are applied after data collection rather than in real time. The rover logs raw GNSS observations during the survey; the base station also logs raw data. Both datasets are processed together in office software to produce centimetre-accurate trajectories.
PPK is preferred when a reliable real-time data link cannot be guaranteed — for example, in remote areas, inside structures, or at long range from a base station. The accuracy is identical to RTK when sufficient satellite observations are logged. Eview GNSS receivers support simultaneous RTK output and raw data logging for PPK processing.
Which Correction Technology Should You Choose?
- Choose RTK when you need centimetre accuracy immediately (real-time machine control, drone mapping with instant quality check, construction layout), have reliable data link coverage, and operate within 50 km of a base station or CORS network.
- Choose PPK when operating in remote areas without reliable internet, flying long UAV missions where RTK link may drop, or as a backup to RTK for audit purposes.
- Choose PPP when operating globally, offshore, or in locations where no CORS network exists and you can tolerate 15–30 minute convergence time.
- Choose RTK + PPK together — the hybrid approach used by most professional UAV operators. Fly with RTK for confidence, log raw data for PPK backup. Eview receivers support this without additional hardware.
How Septentrio Chipsets Implement RTK and PPP
All Eview GNSS receivers use Septentrio chipsets — specifically the mosaic-X5, mosaic-H, AsteRx M3 Pro+, and mosaic-G5 series — which implement RTK, PPK, and PPP in firmware. Key Septentrio advantages:
- FAST6 RTK engine: Septentrio’s ambiguity resolution engine achieves fixed RTK solutions in under 10 seconds on L1/L2/L5 signals, compared to 30–60 seconds for competing chipsets.
- AIM+ (Advanced Interference Mitigation): Protects RTK accuracy in environments with RF interference — jammers, 5G towers, industrial equipment — without requiring external hardware.
- Multi-constellation tracking: All six constellations (GPS, GLONASS, Galileo, BeiDou, QZSS, NavIC) tracked simultaneously for maximum satellite availability and geometric strength.
- OSNMA and Galileo authentication: Septentrio chipsets support Open Service Navigation Message Authentication, providing spoofing detection at the signal level.
Eview GNSS RTK Receivers by Application
- HBEV11 — Septentrio mosaic-X5, 448ch, L1/L2/L5, 4G LTE integrated. Best for UAV and IoT RTK applications.
- GR-P3UTR-M4 — Septentrio mosaic-G5 P3, 789ch. Best for high-precision survey drones and demanding RTK payloads.
- HB6 — Septentrio mosaic-X5, compact box receiver. Best for vehicle-mounted RTK and machine control.
- RB3 — Septentrio AsteRx M3 Pro+. Industrial-grade RTK for demanding environments.
- HB52/HB52H — Septentrio mosaic-H, dual-antenna. RTK positioning with precise heading — no IMU drift.
Frequently Asked Questions
What is the difference between RTK and PPP in GNSS?
RTK (Real-Time Kinematic) uses a nearby base station to transmit real-time corrections, achieving 1–2 cm accuracy immediately. PPP (Precise Point Positioning) uses globally modelled satellite orbit and clock corrections without a base station, achieving 3–10 cm accuracy after a 15–30 minute convergence period. RTK is faster and more accurate; PPP works anywhere in the world without local infrastructure.
How accurate is RTK GNSS?
RTK GNSS achieves 1–2 cm horizontal accuracy and 2–3 cm vertical accuracy in normal conditions. Eview GNSS receivers powered by Septentrio mosaic chipsets are rated at 1 cm + 1 ppm horizontal and 2 cm + 1 ppm vertical RTK accuracy.
What is PPK and how is it different from RTK?
PPK (Post-Processed Kinematic) applies the same corrections as RTK, but after the survey rather than in real time. The rover and base station each log raw GNSS observations during the session; these are processed together in office software to produce centimetre-accurate results. PPK is used when real-time data links are unavailable. Accuracy is identical to RTK.
Do Eview GNSS receivers support RTK and PPK simultaneously?
Yes. All Eview GNSS receivers powered by Septentrio chipsets output real-time RTK NMEA streams and simultaneously log raw GNSS observations (SBF or RINEX) for PPK post-processing. No separate logging hardware is required.
How long does RTK initialisation take?
With a multi-frequency (L1/L2/L5) Septentrio mosaic receiver, RTK ambiguity resolution typically completes in under 10 seconds from a cold start. Single-frequency receivers may take 5 minutes or more. This is why Eview GNSS specifies only multi-frequency Septentrio chipsets.
