PPP & RTK
PPP & RTK
Abbreviations
- SV: space vehicles or orbiting space vehicles
- RTK: Real-Time Kinematic
- PPP: Precise Point Positioning
- PPP-RTK: Hybrid of PPP and RTK
- CORS: Continuously Operating Reference Station
- NRTK: Network RTK
- OSR: Observation State Representation
- SSR: State Space Representation
PPP
- PPP achieves decimetre-level or better accuracy by leveraging corrections transmitted via satellite or the internet.
- It utilises the SSR message format for efficient data transmission.
- PPP is suitable for global applications due to its independence from regional base stations.
- The primary limitation of PPP is its long convergence time, typically ranging from 5 to 30 minutes.
- PPP primarily corrects for orbit errors, clock errors, and biases to achieve its positioning solution.
- PPP offers a trade-off between accuracy and coverage, providing moderate accuracy over a wide area.
- Variations like PPP-AR and A-PPP exist, offering enhanced accuracy or specialized capabilities.
RTK
- RTK provides centimetre-level accuracy, achieving the highest precision among the discussed technologies.
- RTK relies on the OSR message format, which requires a two-way communication channel between the base station and the rover.
- The coverage area of RTK is limited to a short range (30-50 km) due to signal degradation with distance.
- RTK boasts a near-instantaneous convergence time, typically under 5 seconds.
- RTK corrects for various errors, including orbit errors, clock errors, bias, ionospheric delay, and tropospheric delay.
- RTK is widely adopted in applications demanding high accuracy within a limited area, such as surveying and agriculture.
- Developments like Network RTK (NRTK) address range limitations by incorporating networks of base stations.
PPP-RTK
- PPP-RTK combines the strengths of PPP and RTK, offering high accuracy, global coverage, and fast convergence.
- PPP-RTK achieves centimetre-level accuracy comparable to RTK while offering global coverage.
- PPP-RTK employs the efficient SSR message format, enabling broadcast corrections and lower bandwidth requirements.
- PPP-RTK utilises a network of CORS stations for precise atmospheric and clock corrections.
- PPP-RTK converges significantly faster than PPP, typically within 1-10 minutes, and potentially seconds under ideal conditions.
- It effectively corrects for orbit errors, clock errors, bias, ionospheric delay, and tropospheric delay, allowing for integer ambiguity resolution.
- PPP-RTK gracefully degrades to standard PPP performance when outside the range of the CORS network.
Comparing RTK, PPP, and PPP-RTK
| Feature | RTK | PPP | PPP-RTK |
|---|---|---|---|
| Accuracy | cm-level (up to 1 cm + 1 ppm) | dm-level or better (less than 10 cm) | cm-level, similar to RTK |
| Coverage Area | Limited range (typically 30-50 km from the base station) | Global | Global with graceful degradation to standard PPP outside the range of the CORS network |
| Message Format | OSR (Observation Space Representation) | SSR (State Space Representation) | SSR (State Space Representation) |
| Transmission Channel | Two-way communication between base station and rover | Corrections delivered via satellite or the internet | Corrections broadcast to users, enabling a large number of users to connect simultaneously |
| Convergence Time | Near-instantaneous (typically less than 5 seconds) | Relatively long (typically 5-30 minutes) | Fast (typically 1-10 minutes, potentially within seconds under ideal conditions) |
| Errors Solved | Orbit errors, clock errors, bias, ionospheric delay, tropospheric delay | Orbit errors, clock errors, bias | Orbit errors, clock errors, bias, ionospheric delay, tropospheric delay, enabling integer ambiguity resolution |
| Key Strengths | High accuracy, very fast convergence time | Global coverage, no reliance on local base stations | High accuracy, fast convergence time, global coverage, lower bandwidth requirements compared to RTK, graceful degradation outside CORS range |
| Key Limitations | Limited range, high bandwidth requirements, reliance on local base stations | Long convergence time, lower accuracy compared to RTK | Still requires a CORS network (though less dense than RTK) and may degrade to standard PPP with increasing distance from CORS station |
