GCP's vs RTK vs PPK: Which Provides Better Results?

To accurately determine locations and distances in drone surveys, it is essential to record the absolute positions of objects and calculate the distances and angles between each point.

This is where satellite navigation systems like Real-Time Kinematic (RTK) and Post Processing Kinematic (PPK) come into play. Both systems are designed to provide highly accurate raw GPS data, but they differ in the way they work and the types of applications they are best suited for.

In addition to RTK technology and PPK technology, the use of ground control points (GCPs) can further improve the accuracy of the survey drone raw GPS data.

By understanding the strengths and limitations of each system, readers can make an informed decision and choose the right GPS correction technology technique to achieve the level of accuracy and precision required for their specific application.

Whether you’re working on drone surveying or mapping, this blog will provide you with a detailed comparison of the two systems, their advantages and limitations, and the factors to consider when selecting the right system for your needs.

So, let’s dive in and explore the differences between RTK and PPK.

Ground Control Points Explained

Ground control points (GCPs) are an important tool used in drone mapping and surveying to improve the accuracy of the geo referenced images captured by the drone. Essentially, GCPs are physical markers placed on the earth’s surface with known locations that serve as reference points for the drone data.

examples of ground control points — Ground Control Point Examples

A ground control point (GCP) can look like various types of physical markers, such as a specially designed ground marker, a painted target on the ground, or even a natural feature like a rock or a tree. The important thing is that the marker is easily visible and can be accurately located and measured to serve as a reference point for the drone’s GPS data. GCPs are usually placed at strategic locations within the survey area and are typically chosen to provide good coverage of the entire site.

By using GCPs, survey drones can achieve sub-centimeter level accuracy, which is critical for applications such as land surveying and construction site mapping.

However, there are some limitations to using GCPs. For one, setting up GCPs can be a time-consuming and labor-intensive process that requires a team of people to lay out the markers over the course of a day or more. This is especially true for large and complex sites with uneven terrain. Additionally, using GCPs requires a significant amount of post-processing work to tie the ground coordinates of the points to their real-world locations.

To address these limitations, newer GPS correction technologies have been developed that can provide an alternative to GCPs. These technologies use real-time GPS corrections to improve the global accuracy of the drone’s GPS data without the need for physical markers on the ground. This can simplify the process of drone mapping, reducing the amount of time and labor required for setup and post-processing.

GPS Correction Technology

GPS correction technology is a method that improves the accuracy of location data by using GPS receivers to produce precise, high accuracy data. It has been used in various industries for many years to enhance the quality of location data obtained from different tools on job sites. However, only recently has this technology been made available as an add-on for survey drones for survey-grade accurate data.

Compared to traditional GCPs, GPS correction technology can provide the same level of accuracy without requiring the same amount of time and labor for setup. This is because GPS correction technology uses real-time corrections to the drone’s GPS data to enhance high accuracy data without the need for physical markers on the ground. This can save significant time and effort in the field, especially for large and complex sites.

What Do GCPs and GPS Correction Technology Have to Do With RTK vs PPK?

RTK drones and PPK drones have different GPS correction technology techniques, but both have the same goal: to improve the accuracy of GPS data. RTK provides real-time corrections to GPS data by constant and consistent connection from GPS satellites to a ground station.

In contrast, PPK uses post-processing to improve the accuracy of GPS data after the fact. This means that GPS data is collected during a drone’s flight, and then post-processed with the use of software to improve its accuracy

Importance of understanding RTK and PPK

Selecting the right survey drone for a particular project can be a challenge. It’s important for surveyors to understand the differences between RTK and PPK to ensure they are choosing the right system for their needs.

By understanding the advantages and limitations of each system, drone users can make informed decisions about which system will provide the survey accuracy and reliability they need for their projects.

RTK (Real-Time Kinematic)

RTK (Real-Time Kinematic) is a satellite-based navigation system used in mapping that provides extremely accurate GPS coordinates of a RTK drone in real time. It works by comparing signals from the GPS satellites to a fixed reference point or base station, allowing it to provide precise positional data.

This technology is particularly useful for surveying and mapping applications where high levels of accuracy are required.

How RTK Drones Work

An RTK drone is equipped with an onboard GNSS RTK receiver that captures raw GPS (Global Positioning System) data from satellites as well as a GNSS base station on the ground. The ground station serves as a reference point to correct image location in real-time while the drone is in flight. This real-time correction of raw data ensures that the drone is constantly aware of its RTK positioning, which leads to more accurate data collection.

To provide high-precision positioning data, RTK uses a technique called carrier phase tracking that measures the phase difference between the connection from the GPS satellites received by the drone and the base station. This phase difference is then used to calculate the distance between the drone and the ground station.

To ensure accuracy, the RTK system compensates for atmospheric delays that can affect the signal strength between the drone and the GPS satellites, using a technique called atmospheric modeling. This takes into account factors such as the ionosphere and troposphere and corrects for errors introduced by the satellite clock or orbit.

The positioning data is transmitted to the drone in real-time, allowing it to navigate and perform tasks with accuracy.

In summary, RTK works by using a base station to provide a highly accurate location and comparing signals from the GPS satellites to this reference point to calculate the distance between the drone and the base station. The carrier phase tracking technique is used to provide high-precision positioning data, while atmospheric modeling and error correction techniques are employed to ensure the accuracy of the data.

Advantages of RTK

Real-Time Kinematic (RTK) is a satellite-based navigation system that offers several advantages for drone mapping and surveying applications.

Here are some of the main advantages of RTK:

Highly Accurate: RTK provides very accurate GPS coordinates in real-time, making it ideal for applications where precision is critical. With an accuracy of up to centimeters, RTK is the most accurate GPS positioning technology available for drones.

Real-time Data: RTK drone surveys provides highly precise GPS data in real-time, which means that users can quickly and easily collect accurate positioning data as they fly the drone. This allows for faster data collection and more efficient workflow.

Reliability: RTK provides a reliable and consistent connection to the GPS satellites, making it more dependable than other GPS systems. It also compensates for any atmospheric or satellite clock errors that could affect the accuracy of the positioning data.

Easy to Use: RTK is easy to use, with many drones and ground stations coming equipped with RTK capabilities. This makes it easy for users to access highly accurate positioning data without the need for additional equipment or technical expertise.

Versatile: RTK technology can be used in a variety of drone applications, including surveying, mapping, and inspection. Its high accuracy and real-time data capabilities make it suitable for a wide range of tasks.

In summary, RTK’s main advantages are its high accuracy, real-time data capabilities, reliability, ease of use, and versatility. These advantages make it an excellent choice for a wide range of drone-based applications, particularly those that require high levels of precision and accuracy.

Limitations of RTK

While RTK drone surveys offers several advantages for drone mapping and surveying applications, there are also some limitations that users should be aware of.

Here are some of the main disadvantages of RTK:

Requires Base Station: The primary limitation of RTK is that it requires a base station to provide a highly accurate correction data. This means that it is not suitable for applications where there is no access to a base station, such as remote areas or offshore locations. This can limit the usefulness of RTK in certain applications.

Limited Range: RTK has a limited range, typically between 5-10 kilometers, depending on the terrain and the quality of the equipment. This can limit the usefulness of RTK in large-scale applications, such as coastal surveys, agriculture or forestry.

Visual Line Of Site: RTK technology relies on a fixed base station to provide highly accurate location information to a drone in real-time. However, this requires a clear line of sight between the drone and the base station, which means that RTK works best in areas with minimal obstructions such as trees or mountains. If there are obstructions, they can interfere with the signal and affect the accuracy of the location data. Thus, flat terrain with no obstructions is ideal for using RTK technology to achieve the highest level of accuracy.

Reliance on GPS Satellites: RTK relies on a reliable connection to the GPS satellites, which can be affected by various factors such as atmospheric conditions, tree canopy, or tall buildings. This can cause signal dropouts or inaccuracies in the positioning data.

Cost: RTK systems can be expensive compared to other GPS systems. This is due to the need for a base station and high-quality equipment to achieve high levels of accuracy.

In summary, RTK’s limitations are its reliance on a base station, limited range, dependence on GPS satellites, and cost. These limitations can make it unsuitable for certain applications, particularly those in remote or challenging environments. However, in situations where high accuracy is required, RTK remains one of the most reliable and precise GPS positioning technologies available for drones.

PPK (Post-Processed Kinematic)

PPK (Post-Processed Kinematic) is a GPS correction technique that provides that improves the accuracy of GPS coordinates for drones by post-processing the data collected from the drone’s flight. Unlike RTK, PPK does not require a base station to provide accurate location data.

Instead, PPK drones collects GPS data from the drone’s flight, which is then post-processed to improve the accuracy of the GPS coordinates. This makes PPK ideal for applications where access to a base station is limited or not possible.

PPK is commonly used in aerial land survey applications, where it can provide reliable and accurate GPS coordinates for drone flights.

How PPK works

Initial Flight: During the initial flight, The PPK drone will follow a predetermined grid pattern over the survey area, taking pictures or collecting data at specific intervals. As the drone captures images or collects data, it will tag coordinates to each image or data point. This is crucial for post-processing the data, later on, to generate accurately geotags for the surveyed points.
Collecting Data: PPK starts by collecting GPS data from the drone’s flight. This data includes the drone’s position, velocity, and time-stamped measurements of the GPS signal.
Logging Data: The GPS data is logged on the drone’s onboard memory card. This data is often collected at a high frequency, such as 5-10 Hz, to ensure that there is enough data to achieve a high level of accuracy.
Retrieving Data: After the drone has completed its flight, the GPS data is downloaded from the onboard memory card to a computer.
Post-Processing Data: The GPS data is then post-processed using specialized software. This software compares the GPS data collected by the drone with data from a reference station, which provides a highly accurate location. The reference station may be a base station or a virtual station that has been created using data from other GPS stations.
Calculating Corrections: The post-processing software calculates accurately correct image location to the GPS data. This is based on the difference between the drone’s GPS data and the reference station’s GPS data. These corrections include factors such as atmospheric conditions and satellite clock errors.
Generating Precise Coordinates: Once the corrections have been calculated, the post-processing software generates precise GPS coordinates for the drone’s flight. These coordinates are typically accurate to within a few centimeters.
Applying Coordinates: Finally, the precise GPS coordinates are applied to the drone’s images or other data collected during the flight. This allows for accurate georeferencing and mapping of the data.

In summary, PPK improves the accuracy of GPS coordinates for drones by collecting GPS data during the flight and post-processing it with corrections based on data from a reference station. This makes PPK ideal for applications where access to a base station is limited or not possible, such as aerial photography and videography.

Advantages of PPK

Post-Processed Kinematic (PPK) offers several advantages for drone mapping and surveying applications.

Here are some of the main advantages of PPK:

Highly Accurate: PPK provides highly accurate GPS coordinates that are often accurate to within a few centimeters. This level of accuracy is ideal for applications where precision is critical.
Does Not Require Base Station: Unlike RTK, PPK does not require a base station to provide accurate location data. Instead, it uses post-processing to improve the accuracy of the GPS data collected during the drone’s flight. This makes PPK ideal for applications where access to a base station is limited or not possible.
Real-time Data: PPK can also provide real-time GPS data, depending on the capabilities of the equipment and software used. This allows for faster data collection and more efficient workflow.
Reliability: PPK provides a reliable and consistent connection to the GPS satellites, making it more dependable than other GPS systems. It also compensates for any atmospheric or satellite clock errors that could affect the accuracy of the positioning data.
Versatile: PPK can be used in a variety of drone applications, including surveying, mapping, and inspection. Its high accuracy and flexibility make it suitable for a wide range of tasks.

In summary, PPK’s main advantages are its high accuracy, independence from a base station, real-time data capabilities (depending on the equipment and software used), reliability, and versatility.

Limitations of PPK

While Post-Processed Kinematic (PPK) offers several advantages for drone mapping and surveying applications, there are also some limitations that users should be aware of.

Here are some of the main limitations of PPK:

Post-Processing Time: PPK requires a post-processing step to improve the accuracy of the GPS coordinates. This can be time-consuming, and the time required for post-processing will depend on the size of the dataset and the complexity of the correction factors.
Dependence on GPS Satellites: Like RTK, PPK also relies on a reliable connection to the GPS satellites, which can be affected by various factors such as atmospheric conditions, tree canopy, or tall buildings. This can cause signal dropouts or inaccuracies in the positioning data.
Cost: PPK systems can be expensive compared to other GPS systems. This is due to the need for high-quality equipment and software to achieve high levels of accuracy.
Limited Real-Time Capabilities: PPK does not provide real-time data by default, although real-time data can be achieved through the use of specialized equipment and software. This means that users may have to wait for post-processing before they can access highly accurate positioning data.

In summary, PPK’s limitations are its post-processing time, dependence on GPS satellites, cost, and limited real-time data capabilities by default. These limitations can make it less suitable for certain applications, particularly those that require real-time data or where time is of the essence.

However, in situations where high accuracy is required and access to a base station is limited, PPK remains a reliable and precise GPS positioning technology for drones.

RTK vs PPK: Which is Better?

RTK and PPK can be addressed by comparing their respective methods of correction. RTK (Real-Time Kinematic) corrects data during the flight, while PPK (Post-Processed Kinematic) corrects data after the flight. This means that RTK provides real-time accuracy, while PPK provides accuracy after the data has been collected. The choice between the two will depend on the specific use case and needs of the user.

Here’s a summary of the main difference between RTK and PPK:

RTK provides highly accurate GPS coordinates in real-time, while PPK requires a post-processing step to achieve high accuracy.
RTK requires a base station to provide accurate location data, while PPK is independent of a base station.
RTK has a limited range of typically 5-10 km, while PPK has no such range limitation.
RTK is generally more expensive than PPK due to the need for a base station and specialized equipment.
PPK does not require strong signal strength or reliable GPS communication between the drone and the base station.
RTK is generally faster than PPK since it does not require a post-processing step.

When deciding which system to use for a project, it is important to consider factors such as the required level of accuracy, the available budget, the time frame for data collection, and the ease of use in the field.

In general, PPK is the better option. Combining PPK images with GCPs (Ground Control Points) can lead to the best absolute accuracy when conducting a survey or mapping project using a drone. While PPK alone can provide highly accurate GPS coordinates, incorporating GCPs further improves the accuracy of the data by providing known points on the ground that can be used as reference points during post-processing. By combining PPK and GCPs, you can ensure that your data is as accurate as possible and meets the specific requirements of your project.

Which one is better for your project?

When choosing between RTK and PPK for your project, it’s important to consider several factors to determine which system is better suited to your specific requirements. Here are some of the key factors to consider:

Accuracy: The level of accuracy needed for your project will be an important factor in choosing between RTK and PPK. If you need highly accurate GPS coordinates in real-time, RTK may be the better option. If you can tolerate a post-processing step and require independence from a base station, PPK may be a better fit.
Cost: RTK systems can be more expensive than PPK systems due to the need for a base station and specialized equipment. If cost is a significant factor, PPK may be a more economical choice.
Data Processing Time: RTK provides real-time GPS data, while PPK requires a post-processing step to improve the accuracy of the GPS data. If time is a critical factor and real-time data is required, RTK may be the better option.
Ease of Use in the Field: RTK may be easier to use in the field since it does not require a post-processing step. PPK, on the other hand, requires data to be downloaded and processed after the flight. If ease of use is a concern, RTK may be a better choice.

Ultimately, the choice between RTK and PPK will depend on the specific requirements of your project. If high accuracy and real-time data are required and cost is not a concern, RTK may be the better option. If independence from a base station and cost are more important, PPK may be a better fit.

Conclusion

The choice between RTK and PPK for drone mapping and surveying applications ultimately depends on the specific requirements of the project. RTK provides highly accurate GPS coordinates in real-time, but requires a base station and can be more expensive. PPK, on the other hand, is independent of a base station and can be more cost-effective, but requires a post-processing step to achieve high accuracy.

It’s important to consider factors such as accuracy, cost, data processing time, and ease of use in the field when making a decision.

By understanding the differences between RTK and PPK, drone users can choose the right system for their project and ensure that they achieve the level of accuracy and precision needed to succeed.

GCP’s vs RTK vs PPK: Which Provides Better Results?