Understanding the Differences Between PPK vs RTK

In the world of drone mapping and aerial surveying, GNSS correction technologies such as PPK (Post-Processed Kinematic) and RTK (Real-Time Kinematic) play critical roles in ensuring high-precision data. Both systems offer distinct advantages and are suited for different use cases depending on accuracy requirements, operational environments, and real-time data needs. This article explores the differences between PPK and RTK, guiding users in choosing the best GNSS correction technique for their specific applications.

Understanding GNSS Correction Technology

GNSS correction technologies are used to improve the accuracy of location data collected by drones and other GNSS-equipped devices. These technologies apply corrections to raw satellite data, which would otherwise be prone to errors due to ionospheric, tropospheric and orbital data, or timing inaccuracies.

Without correction technologies, standard GNSS systems might only offer accuracy within a few meters, which is insufficient for industries like surveying, construction, agriculture, and aerial mapping, where precise positioning is critical. By leveraging GNSS correction or even high-quality GNSS services, the corrected data provides users with high-precision location data that meets the stringent accuracy requirements of professional applications.

Let’s take a look at a real-world example: drone mapping. 

Drone mapping involves using unmanned aerial vehicles (UAVs) equipped with cameras and sensors to capture high-resolution images and data of the Earth's surface, creating detailed maps and 3D models. Its real-world applications include construction site monitoring, agricultural assessments, environmental conservation, and infrastructure inspections, providing valuable insights for planning, analysis, and decision-making.

PPK Drone Mapping

PPK (Post-Processed Kinematic) is a GNSS correction technique that corrects trajectory data after a drone flight. It utilizes the raw GNSS data collected by the drone and compares it with data from a stationary base station to produce corrected positional information. PPK-capable drones do not require a constant communication link with a ground control point, making this method particularly effective in remote areas where stable connections are hard to maintain. Post-flight correction data is processed to provide accurate geolocation, delivering highly precise results.

What It Is and Its Features

PPK drone mapping involves gathering raw GNSS data during a flight and correcting that data after the drone lands. This method relies on a stationary reference point (base station) to calculate the corrected  position of the drone. One of the main features of PPK technology is its offline workflow, as it does not depend on real-time connections to provide corrected data. This makes PPK suitable for long-duration flights or operations in areas with poor signal strength.

RTK Drone Mapping

RTK (Real-Time Kinematic) is another GNSS correction technique that corrects data in real time. RTK drones use an onboard GNSS RTK receiver and work in conjunction with a base station to provide real-time corrections during the flight. This method allows for immediate and accurate positional information, making it highly effective for real-time applications that require instant geolocation data, such as construction site surveys and precision farming.

What It Is and Its Features

RTK drones rely on constant communication between the drone, a base station, and sometimes a mobile network. The base station sends raw data to the rover in the drone and the rover computes the corrections which are used to calculate the drone positioning solution in real time.drone sends raw data to the base station, which then processes the information and sends corrections back in real-time. This allows users to receive corrected GNSS data during the flight. RTK technology provides centimeter-level accuracy, but it requires a stable connection and can be limited by range and signal strength. It's often dependent on additional infrastructure like a CORS (Continuously Operating Reference Station) network supporting VRS (Virtual Reference Station).

PPK vs RTK: Key Differences

While both RTK and PPK offer high-precision GPS correction, their core differences lie in how and when corrections are applied. Below are the main distinctions between the two systems:

1. Accuracy and Precision

Both RTK and PPK provide survey-grade accuracy, but they achieve this through different workflows. PPK drones offer the advantage of post-flight correction data, which tends to provide higher precision since corrections can be computed with more advanced algorithms. RTK drones, on the other hand, provide near-instantaneous corrections, which is beneficial in scenarios where real-time data is essential.

In general, both methods can achieve centimeter-level accuracy, but PPK is considered to have a slight edge in terms of absolute accuracy due to the post-processing of location data. However, for use cases that demand immediate results, RTK is favored for its real-time capabilities.

2. Real-Time vs. Post-Processing

The main difference between RTK and PPK lies in the timing of the correction data. RTK applies corrections in real-time as the drone is in flight, making it ideal for projects where immediate data is required. PPK, however, processes the raw data after the drone lands, which means users have to wait for post-processing to see the final corrected results.

The workflows also differ—RTK relies on a telemetry link to ground control points and requires a stable connection throughout the flight, while PPK corrects data offline, offering more flexibility in areas with limited or no signal.

3. Equipment and Setup

RTK and PPK both require specialized hardware. RTK drones need an onboard GNSS RTK receiver, a base station, and sometimes access to a CORS (Continuously Operating Reference Station) network. A CORS network is a system of continuously operating GPS or GNSS stations that provides real-time, high-precision positioning data for accurate geolocation over a wide area. The setup includes a drone and a base station that work together in real-time, which means both devices must remain in communication for the duration of the flight.

PPK drones, on the other hand, also use GNSS technology but don’t require constant communication between the drone and the base station. The data from the flight is processed afterward, making the setup simpler, with no need for continuous signal or mobile network support.

4. Connectivity and Range

RTK's main limitation is its reliance on a stable, continuous signal between the drone, the base station, and sometimes a mobile network. In remote areas or locations with poor signal strength, RTK's performance may suffer, leading to a loss of real-time corrections. RTK technology is often limited to a specific range from the base station.

PPK, however, operates independently of real-time connections. This allows PPK drones to be used in more remote or challenging environments without worrying about connectivity issues. PPK's offline capabilities make it ideal for long-duration flights or in situations where signal interruptions might occur.

5. Practical Applications and Suitability

PPK and RTK are suited to different types of projects. PPK is often used in large-scale mapping operations, archaeological surveys, and areas where high precision is needed but real-time data isn't required. Industries that commonly use PPK include mining, agriculture, and topographic mapping.

RTK, on the other hand, excels in applications requiring real-time accuracy, such as construction site surveys, precision agriculture, and infrastructure monitoring. RTK is especially useful for short-term missions in areas with strong signal coverage, where instant feedback is necessary.

Advantages and Disadvantages of PPK and RTK

Each GPS correction technique has its strengths and limitations, making them better suited for different environments and specific project needs. Below is an expanded overview of the pros and cons of both PPK and RTK.

PPK Pros

• High accuracy is achievable without requiring real-time connections: PPK uses raw GPS data collected during a flight, which is processed later against a reference point to ensure highly accurate results. This post-processing method allows for the correction of any positional errors that may occur, ensuring precision without the need for live corrections.

• Works well in remote areas with poor or no signal: Since PPK does not depend on continuous connectivity with a base station or network during the flight, it can be used in areas where maintaining a stable communication signal is difficult or impossible. This makes it ideal for mapping and surveying in remote or inaccessible regions.

• Suitable for long-duration flights and large mapping areas: PPK is especially useful for large-scale projects that involve extensive mapping areas or long-duration flights. Because it processes data after the flight, it doesn't require the drone to stay within a limited range of a base station, making it perfect for broad or extended missions.

PPK Cons

• Post-processing is required, which can delay results: One of the main drawbacks of PPK is the need for post-flight data processing. After the drone lands, the raw data must be downloaded and processed to apply corrections, which can delay the delivery of final results. This makes PPK less ideal for time-sensitive projects that require immediate data.

• Cannot provide real-time corrected data during the flight: Unlike RTK, PPK does not offer real-time location corrections. This means that during the flight, users won’t have access to correct data, which may be a disadvantage in situations where live data is critical for decision-making or where immediate feedback is required.

RTK Pros

• Provides real-time accuracy, delivering instant results during the flight: RTK technology corrects positional data in real-time, allowing users to get accurate information as the drone flies. This real-time correction is highly valuable in scenarios where quick, precise location data is necessary, such as construction or precision agriculture, where immediate adjustments may need to be made on-site.

• Ideal for projects where immediate geolocation data is needed: For industries that rely on fast, actionable data, RTK is the preferred method. It allows surveyors, farmers, and construction managers to receive instant updates on positional accuracy, facilitating quicker decisions and minimizing the need for post-flight data analysis.

RTK Cons

• Requires a stable signal and continuous connection with the base station: RTK depends on a steady telemetry link between the drone, base station, and sometimes a mobile network. If the signal is interrupted, the accuracy of the real-time corrections can be compromised, which limits its effectiveness in areas with poor connectivity.

• May face performance issues in remote or signal-challenged areas: Because RTK requires constant communication with a base station, it may not perform well in remote or signal-challenged environments. If the connection is lost or weakened, the drone’s ability to maintain real-time corrections is impacted, which could reduce the accuracy of the data collected during the flight.

Choosing the Right GPS Correction Technique

Choosing between PPK and RTK depends on the specific needs of the project. If real-time data and immediate feedback are critical, RTK is the better option. It is well-suited for projects that take place in areas with good connectivity and require fast results.

However, if the project requires extreme precision and is conducted in remote areas where signals are weak or unavailable, PPK is the better choice. Its ability to process data offline and provide high-accuracy results without real-time connection makes it more versatile in these scenarios.

For high-precision GNSS solutions tailored to your drone mapping needs, whether you're using PPK for post-flight corrections or RTK for real-time data, onocoy offers a decentralized, hardware-agnostic GNSS network that guarantees accuracy and flexibility. With global coverage and cost-effective services, onocoy's solutions ensure that your GPS correction needs are met, no matter where your project takes you.

Ready to enhance your drone operations? Contact us, explore the future of GNSS, and take your precision to the next level.