PPK vs RTK in drone mapping: choosing right technology for precision surveys

In aerial mapping, your workflow mainly depends on the technology your drone employs—PPK (Post-Processing Kinematic) or RTK (Real-Time Kinematic). Each system has its own strengths and therefore is designed for specific scenarios. Understanding how each approach works will help you achieve accurate and reliable mapping results.

RTK vs PPK

Both RTK and PPK are designed to enhance the accuracy of GNSS data, and while they work differently, the results they deliver are quite similar. The main difference lies in when data corrections are applied:

• RTK provides real-time corrections as the drone flies, requiring a constant telemetry link between the drone and the base station.
• PPK, on the other hand, applies corrections after the flight during data post-processing.

Despite these differences, both methods achieve comparable levels of accuracy, and the choice between them is about your drone’s specific capabilities.

RTK drones, like those from DJI and Autel, are all about speed, efficiency, and mobility, making them ideal for quick data acquisition and smaller-scale projects. Most of RTK drones can also record logs for PPK either by default or through optional configurations. This allows you to have backup data that can be post-processed to compensate for any data loss caused by signal interruptions during the flight.

Manufacturers of fixed-wing drones often equip them with PPK, making them ideal for large-scale projects. These drones provide extended autonomy, long battery life, and the capability to carry advanced sensors such as magnetometers.

Let’s take a closer look at the aspects of each workflow.

Real-time precision on the fly

RTK drones use a built-in RTK GNSS receiver onboard the drone which communicates with a local base station directly or with a continuously operating reference station (CORS or VRS) through an NTRIP protocol (Network Transport of RTCM via Internet Protocol) in real time. This ensures precise geotagging of images during flight and providing ready-to-use data immediately after the mission. Learn more about RTK in our documentation.

In practice, RTK relies on maintaining four stable communication links:

1. The drone must receive GNSS signals.
2. A stationary base station or correction network (CORS/VRS) must receive GNSS signals.
3. The base station or CORS/VRS must send corrections to the drone’s controller.
4. The controller must relay corrections to the drone via telemetry.

Maintaining these connections is essential for achieving accurate real-time positioning with RTK, with reliable telemetry often requiring the most attention. Key practices include ensuring a clear line of sight between the drone and its controller and minimising electromagnetic interference.

A clear line of sight between the base and rover means no physical obstructions, like buildings, trees, or hills, block the signal path. This is essential for reliable communication in RTK systems, where uninterrupted data flow ensures precise positioning.

Electromagnetic waves from nearby electronic devices or infrastructure can degrade RTK performance by reducing signal quality, causing delays, or introducing positioning errors. To prevent this, avoid operating near cell towers, radio transmitters, high-voltage power lines, industrial equipment, machinery, Wi-Fi routers, or other wireless devices.

In addition to the connections mentioned above, streaming RTK corrections from the base to the drone via the drone’s controller typically requires an internet connection. However, the Reach RS3 base features a Local NTRIP Caster option, allowing you to work offline. Learn more about correction streaming options in a step-by-step guide featuring the integration of a DJI RTK drone and the Reach RS3 base. The guide covers both methods in detail.

Post-processed precision

PPK drones don’t require a real-time link between the drone and the stationary base station or CORS. Instead, both the drone and base station independently record raw GNSS data by receiving signals from satellites, eliminating the need for telemetry during the flight. After the flight, these data sets—each with an initial accuracy of about 1 meter—are processed in specialized software. This post-processing step aligns and corrects the data to produce highly precise geotagged images. Learn more about PPK in our documentation.

PPK eliminates the need for real-time correction signals, making it ideal for surveying large areas with complex terrain where maintaining a clear line of sight between the drone and its controller is challenging. For example, mapping a marshy area with unstable ground that prevents on-foot access or identifying sagging or damaged wires in a dense forest or rugged terrain where vehicles or humans cannot easily reach is often accomplished using PPK drones.

However, when using a PPK drone, it’s still essential to ensure both the drone and the base station have an unobstructed view of the sky, free from obstacles or interference. Additionally, you’ll need to allocate time for post-processing the dataset after the flight.

Use of ground control points

Both RTK and PPK workflows still rely on ground control points (GCPs), which are physical markers on the ground essential for accurately aligning and positioning maps within real-world coordinates. GCPs play a crucial role when creating orthophotos or 3D models in photogrammetry software, especially for large sites or areas with complex terrain. This remains true regardless of the type of drone used.

Quick comparison of PPK vs RTK in drone mapping

We’ve put together a quick overview for you, highlighting the key differences between these two technologies:

Factor	RTK	PPK
Real-time accuracy	Ideal for projects requiring instant results, as corrections are applied during flight.	Not suitable for immediate results since corrections are applied after flight.
Connectivity	Requires stable telemetry between the drone’s controller receiving corrections from the base, and the drone.	No real-time corrections from the base to the drone needed; corrections are applied using logged data.
Terrain and obstacles	Best for open areas with minimal obstructions to maintain a strong signal.	Handles complex or obstructed terrains better, as it doesn’t rely on telemetry.
Project area size	Suitable for small to medium-sized areas within close range of the base station.	Better for large-scale mapping, as base station distance is less of a limitation.
Remote locations	Less effective in remote areas without reliable network or base station connectivity.	Ideal for remote areas, as no live correction signal is required.
Post-processing	Minimal post-processing required, streamlining the workflow.	Requires post-flight processing, adding an extra step to the workflow.
Equipment cost	Typically requires an RTK-enabled drone and a connection to a correction source, adding upfront costs.	Requires a GNSS receiver for logging data, but no reliance on correction networks.
Workflow speed	Faster workflow, ideal for time-sensitive projects.	Slower workflow due to the more complex setup and need for post-flight data processing.
Reliability	May suffer from signal loss or reduced accuracy if connection to the base station is interrupted.	More reliable in maintaining accuracy, as corrections are calculated offline.
Best use cases	Construction monitoring, small to medium surveys, time-sensitive projects, or areas with good connectivity.	Large-scale surveys, remote locations, complex terrains, or high-stakes projects.

In summary, choose RTK for drone mapping projects when you need fast results, have reliable network access, and are working in smaller, open areas. Opt for PPK for aerial mapping in remote locations, large project sites, or challenging terrains where signal reliability may be an issue, and you can allocate time for post-processing.

Operate your RTK or PPK drone with the Reach RS3 base

The Reach RS3 works effectively as a base for drones in both RTK and PPK workflows and offers two options to send corrections to your RTK drone. You can do this via Emlid Caster over the internet or use the Local NTRIP option in Emlid Flow to set up RTK without an internet connection.