What Are RTK and PPK?
First, let’s clarify what we’re talking about. Real-Time Kinematic (RTK) and Post-Process Kinematic (PPK) are both methods for improving the accuracy of GNSS measurements:
- Both techniques work by using two receivers relatively close to each other (within about 20 miles)
- The system assumes both receivers experience the same errors, allowing these errors to be canceled out
- RTK provides corrections in real-time
- PPK records data for later processing using specialized software
In this setup, we typically have:
- A stationary base station (sending corrections)
- A rover (your drone) receiving those corrections
RTK Correction Methods: Which to Choose When?
There are two primary approaches to getting RTK corrections to your drone:
1. Network-Based Corrections
Best when: You have reliable cellular connectivity in your mapping area
- Your controller connects to an NTRIP service or network-based correction source
- Corrections are delivered via the internet
- Many modern systems (like DJI) are designed with this workflow in mind
2. Local Base Station
Best when: You’re working in areas with poor or no cellular coverage
- A local GNSS receiver serves as your own private correction source
- The base station creates a local network your controller can connect to
- Modern systems can act as a local NTRIP caster, broadcasting corrections to your drone controller
Experienced professionals don’t rely on just one method. Even if you primarily use RTK, always ensure you have PPK capability as a backup.
Everyone really likes RTK… until it fails. Connectivity issues are inevitable in fieldwork, and having PPK as a fallback ensures you won’t waste a site visit.
Multiple Roles of a Modern GNSS Receiver
Today’s advanced receivers can perform multiple functions simultaneously:
- Act as a base station sending corrections to your drone
- Receive corrections from a CORS network to improve its own position
- Record raw data for post-processing
- Provide corrections to a rover unit used for ground control points
This versatility creates a robust workflow with multiple redundancies built in.
The Critical Role of Ground Control Points
Despite advances in onboard RTK/PPK capabilities, ground control points remain essential—not just for maximum accuracy but for quality verification. They provide crucial checkpoints to verify your work’s accuracy, especially important when completing numerous flights across multiple sites.
Using a local base station significantly improves accuracy because:
- The baseline (distance between base and rover) is minimized
- Your drone, images, and ground control points all maintain tight relative positioning
- Errors are significantly reduced compared to using distant CORS stations
Which Workflow Is Best for Remote Areas?
If you’re working in extremely remote locations far from any CORS station, you have two primary options:
Option 1: RTK Workflow with Local Base
- Arrive early to log static data
- Process through OPUS or similar service to establish an accurate base position
- Enter these coordinates into your base station
- Conduct your RTK flight
Option 2: PPK Workflow
Often more efficient in remote areas because:
- You can set up your base and fly simultaneously
- No need to wait for OPUS processing before flying
- Process everything back at the office
- Saves significant field time
The choice between RTK and PPK isn’t about which is “better”—it’s about selecting the right tool for your specific situation.
While RTK offers immediate positioning confidence (valuable for close-proximity flights like building inspections), PPK provides superior robustness and often greater accuracy, especially for standard mapping missions at typical altitudes.
What matters most is having the flexibility to adapt to field conditions and understanding when to employ each approach.
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