Introduction
RTK gives centimeter accuracy but requires a nearby base station. What if you need high accuracy in the middle of the ocean, a desert, or anywhere without base stations? That's where PPP comes in.
What Is PPP?
Precise Point Positioning is a technique that achieves high accuracy using only a single receiver, no base station needed. Instead of real-time corrections from nearby bases, it uses precise satellite orbit and clock information from global networks.
The PPP Concept
Standard GPS uses:
- Broadcast orbits (accuracy ~1 meter)
- Broadcast clocks (accuracy ~2 nanoseconds)
PPP uses:
- Precise orbits (accuracy ~2–5 cm)
- Precise clocks (accuracy ~0.1 nanoseconds)
These precise products come from global networks of tracking stations that continuously monitor all GNSS satellites.
PPP vs. RTK
| Feature | RTK | PPP |
|---|---|---|
| Base station needed | Yes | No |
| Range | 10–30 km | Global |
| Accuracy | 1–5 cm | 5–20 cm |
| Convergence time | 30–60 seconds | 20–40 minutes |
| Works anywhere? | No (needs base) | Yes |
The Convergence Problem
PPP's biggest limitation: it takes time to converge. The receiver needs to precisely estimate atmospheric delays, carrier phase ambiguities, and receiver clock errors.
- 10 cm after 20–30 minutes
- 5 cm after 60+ minutes
PPP Services
| Service | Provider | Accuracy | Delivery |
|---|---|---|---|
| Trimble RTX | Trimble | 2–5 cm | Satellite/internet |
| NavCom StarFire | John Deere | 5–10 cm | Satellite |
| CNES PPP-WIZARD | CNES | 10–20 cm | Internet (free) |
| Natural Resources Canada | Gov't | 10–20 cm | Internet (free) |
PPP in Practice
- Marine applications: Perfect for open ocean where no bases exist
- Remote area mapping: Deserts, mountains, forests
- Agriculture: Some tractor guidance uses PPP
- Scientific research: Plate tectonics, ice sheet movement
- Aviation: Oceanic navigation
Vital Points
- PPP provides high accuracy without a base station
- Uses precise orbits and clocks from global networks
- Accuracy: 5–20 cm after convergence
- Convergence time: 20–40 minutes, main limitation
- Ideal for remote areas with no base stations
- PPP-RTK combines best of both worlds (see next lesson)