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If you’re a drone enthusiast, you’ve probably heard terms like PPK, RTK, and GCP. Well-known drones on the market, such as the M300 RTK and Phantom 4 RTK, have these acronyms in their titles. However – What exactly are PPK and RTK? What are RTK and PPK drones used for? Which gives the best results? Are these questions confusing you? This article is for you. Simply put, the main difference between them occurs during position correction. RTK is fixed in flight, PPK is fixed later. Both methods correct for position errors in drone mapping data and eliminate the need for GCPs, resulting in cm (sub-inch) absolute accuracy.
Drones are proving to be an invaluable asset in a variety of industries, including public safety, oil and gas, energy and utilities, construction, and agriculture. Drone-based solutions are an economical, practical, efficient and accurate alternative to existing workflows. Always remember that the efficiency of your investigation is related to choosing the right remediation method. But before getting to the heart of the matter, it’s essential to understand the concepts of GPS, GNSS, and GCPs.
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What are GPS and GNSS?
The Global Navigation Satellite System (GNSS) is a network of satellites that broadcast time and orbit data required for navigation and positioning. Simply put, a GNSS receiver accurately calculates its position by measuring the distances to three or more satellites. In contrast, Global Positioning System (GPS) is a type of GNSS and is also the most frequently used GNSS in the world. GPS is a navigation system that uses satellites, receivers, and algorithms to synchronize position, velocity, and time data of movement in the air, sea, and land. Provides real-time location and timing information around the world.
A fundamental difference between GPS and GNSS is that GNSS-enabled devices can use navigation satellites from non-GPS networks. The higher the number of satellites, the more accurate and reliable the receiver. All GNSS receivers are compatible with GPS. However, GPS receivers are not always compatible with GNSS.
What is GCP
A ground control point (GCP) is a designated point on the ground with a defined geographic location. They are often required for aerial survey applications as they further enhance the location and accuracy of the mapping output. In aerial surveys, drones are deployed to autonomously capture images of survey areas. Also, if you use GCPs, these aerial photos must show the GCPs. Photos are processed in the cloud using drone mapping software.
Placing GCPs in the mission area may take some time. This task requires a crew, vehicle, and equipment, along with document requirements for approvals and permits. Fortunately, alternatives such as PPK and RTK drones are now here to help with this time-consuming operation. Now back to the main question: Which drone technology, RTK or PPK, offers a better mapping experience? The answer depends entirely on your specific mission, including your local network connection. Regardless, RTK and PPK have some strengths and weaknesses. I’m here to analyze this topic and help you decide which one is really best for your drone mapping team.
What is an RTK drone?
RTK or real-time kinematic drones are equipped with a built-in GNSS RTK receiver that collects data from satellites and base stations to correct the image position in real-time as the drone flies.
With data connectivity such as GSM or WiFi, RTK drones connect to a base station or virtual reference station (VRS) via a device that controls flight. The camera position is determined in real time with an accuracy of up to 2-3 cm both horizontally and vertically. Simply put, if all signals are stable when the drone lands, the absolute accuracy data can be post-processed to map the findings. Advantages of using RTK drones:
- Save time by eliminating the need to place GCPs in hard-to-reach locations
- The drone’s real-time GPS positioning is used to make real-time corrections.Eliminates the need for post-flight GNSS processing
- Better waypoint navigation, beneficial in challenging settings
- Autonomous landing with RTK assistance
However, as it relies on a data connection, RTK positioning has its own drawbacks, such as radio link outages and signal blockage. In addition, long distances between drones and base stations can cause signal interference, resulting in loss of correction data and a lower percentage of accurate camera positions during flight. In such scenarios, PPK compensation can be selected if the drone is capable enough.
You may find it useful to be able to receive correction data during your flight. However, in real-world situations, RTK technology has flaws to consider, as barriers can block or interrupt the signal and flight can extend beyond the strength of the signal. RTK achieves the same absolute accuracy as PPK in the best case (when the link between base station and drone is continuous).
What is a PPK drone?
A PPK or post-processing kinematic drone uses an onboard GNSS receiver to append geographic coordinates to each image. Base stations (GNSS base stations or CORS networks), on the other hand, also collect location information during flight with more accurate triangulation. Once the drone has landed, corrective procedures should be performed using the appropriate software. This program can be cloud-based or desktop-based, depending on your preference. He then matches his two acquired GPS data sets to correct for satellite signal inaccuracies and reduce accuracy down to the sub-inch range.
An RTK Drone system requires four uninterrupted communication lines to function efficiently. 1. The line between satellites and drones. 2. Lines between satellites and GNSS base stations or CORS networks. 3. Lines between GNSS base stations, CORS/VRS and drone base stations. 4. The line between the drone base station and the drone.
Two uninterrupted lines of communication are required for the PPK drone system to function efficiently. 1. Links between satellites and GNSS base stations/CORS networks. 2. The line between satellites and drones.
Advantages of using PPK drones:
- Save time by eliminating the need to place GCPs in hard-to-reach locations
- Ensures effective flight even in difficult scenarios where real-time corrections are not possible
- Retention of GNSS data for validation and reprocessing as needed
- Flexibility in using base stations
- There are no long-range radio requirements and no risk of data link outages.
- Accurate GNSS positioning of drones after flight
- GPS processing with dual antennas
As already mentioned, the disadvantages of RTK flight are mainly related to connection loss due to obstacles. In such cases, PPK improves results. That said, it’s also important to note that RTK flights can effectively capture terrain and provide highly accurate findings if the datalink connection is stable.
Frequently Asked Questions
1. Which is better, PPK or RTK?
Well, it depends on the task at hand. For example, RTK may appear to save time as it retrieves corrected data as soon as the drone lands. However, RTK tends to fail when considering link dependencies. PPK systems, on the other hand, are more flexible and can carry out their missions in the most difficult environments.
If the mission area has dense vegetation or other obstacles, mapping with an RTK/PPK drone is recommended. This is because no matter where you place your GCPs or whether or not you place them, you always have control over high-precision, high-quality output.
2. When should I use ground control points in my GIS operations?
There are two main reasons for using GCP. (1) if you require the highest degree of global accuracy, or (2) if you have a contract to provide measurements within a specified accuracy range.
3. What is the difference between ground control points and checkpoints?
A survey checkpoint is a point with established coordinates used to verify the accuracy of a survey. Ground control points (GCPs), on the other hand, use GPS data to calibrate the survey model and improve overall accuracy. Note that unlike GCP, checkpoints do not affect data processing.
4. How many ground control points are required?
The answer depends on your requirements and the size of your research area. However, mapping and surveying missions require a minimum of 5 of her GCPs.
5. What are the disadvantages of using ground control points?
Before using GCP, you should consider certain factors such as project feasibility, time, and cost. For example, GCP measurements are not always possible onsite due to various factors such as delicate ground textures, inaccessible areas, and other personal safety considerations.
6. Will RTK and PPK drones replace ground control points?
No, drones will not replace the use of GCP. Even when using technologies such as RTK and PPK, the ground control point concept is still relevant. Depending on the size of the site, ground validation may be required to ensure that survey drones continue to deliver highly accurate outputs. Ideally, drone surveys and land surveys should go hand in hand!
7. Does PPK require a base station?
Yes, both RTK and PPK require a base station.
8. Are PPKs restricted by line of sight?
No, this is where PPK drones have advantages over RTK, especially on long flights. PPK drones can easily perform beyond-line-of-sight (BVLOS) operations.
To learn more about PPK and RTK and incorporate these surveying methods into your workflow, contact your in-house survey team or learn more about FEDS drone surveying and mapping.
Post RTK v/s PPK Drones: Which is Best? First Appeared on Leading Drone Company | Drone Service Provider.
