Drone technology has become an essential tool for surveyors, revolutionizing the way we map, measure, and manage the modern worksite. Post-processed kinematic (PPK) workflows in particular have emerged as the clear leader in delivering the best efficiency and accuracy across the broadest range of use cases.
But nuances exist even within the world of PPK drone surveying, and those differences can significantly impact the overall ease and accuracy of each survey.
As the gold standard drone-based PPK solution (according to the Engineering and Mining Journal), we know a thing or two about how to get the most out of a PPK survey with as little hassle as possible. The smart device that’s given our PPK workflow the edge is our ground control solution: AeroPoints.
In this post, we’ll explore the differences between PPK surveying with and without AeroPoints and explain why Propeller’s smart ground control has put our PPK workflow ahead of the alternatives.
What is PPK drone surveying?
First, a brief recap of PPK: what it is, how it works, and why it’s the most accurate drone surveying method on non-vegetated sites. (Lidar can be more accurate if you’re flying over dense canopy.)
PPK is a type of drone surveying workflow that improves the accuracy of location data. Unlike traditional surveying techniques, PPK leverages GPS data post-flight to enhance the accuracy of your location tags. When you survey using PPK drone mapping, the images and GPS data collected by your drone are corrected against data from a base station after you fly instead of in real-time.
This workflow is different than RTK (real-time kinematic) surveying, which relies on real-time processing to pin the drone’s geocoordinates to known points on the ground. As confusing as this might sound at first, PPK workflows use RTK-enabled drones. That’s because RTK drones can track their own positions accurately, where standard drones can’t. RTK drones record GPS data and geotag images as they’re captured during flight, assigning each image a GPS location based on the drone’s internal sensors.
In an RTK workflow, an active base station on the ground sends raw GPS data to the drone. The drone’s onboard GPS then combines that info with its own observations to determine its position in space and geotag your images.
Real-time might sound like the best option, but it actually introduces the opportunity for error. To achieve data accuracy, the RTK drone must stay connected to the base station during flight. If the drone and base station lose connectivity for even a moment, your overall survey accuracy is compromised. This can happen for lots of reasons: antenna orientation, unreliable signal, disruption from rugged terrain or other visual barriers, and even the natural movement of the drone. All of this introduces a margin of error.
The benefits of PPK
In a PPK workflow, the drone still geotags your X,Y,Z coordinates to each image based on that on-board GPS unit. While this is happening, a base unit is also recording positional information—but with much more accurate triangulation. PPK corrects the drone’s positional data after flight by using the photo timestamps, dramatically reducing the margin of error in the final dataset.
PPK drone surveying has several advantages over RTK, including:
- Accuracy: By processing geospatial data after you land, PPK ensures higher precision in your survey results, yielding accuracy to 1/10ft.
- Performance: PPK is effective every time—even in areas where real-time data transmission is challenging, such as remote areas, spots with signal interference, or long flights over rugged terrain.
- Efficiency: Done right, PPK can be much more efficient than other drone surveying methods because it eliminates the need to manually place ground control points (GCPs) in the right distribution across your site. (More on this in the next section.)
Want to dig into the details?
We’ve got you covered. Check out our PPK digital guide to cut through the confusion and get straight to what you need to know about PPK.
A note about ground control
Ground control is an essential ingredient in all types of drone surveying. For greater accuracy, you need to use a sufficient number of known points on the ground, marked so the drone’s camera can “see” them. Those points are then used to verify the location data from the drone’s patchwork quilt of images.
If a drone’s position in the sky can’t be accurately geotagged, you can’t get reliable survey data. That accuracy comes from ground control, which is why even minor errors in your ground control placement can have significant repercussions.
What a difference an AeroPoint makes
While PPK is a highly accurate workflow, it still relies on solid ground control to yield survey-grade accuracy. In most cases, this means spending hours manually shooting and marking GCPs, which can be both time-consuming and dangerous on a busy worksite or unstable ground.
AeroPoints, our smart ground control solution, have changed all that. These portable, solar-powered GCPs are equipped with built-in GPS and serve as a base unit and GCP all in one. Simply place at least one in your flight area before launching your drone, and voila! Instant ground control.
AeroPoints seamlessly integrate with your drone and PPK workflow to simplify the process of collecting high-accuracy survey data from the air.
Incorporating AeroPoints into your PPK workflow expands the list of PPK benefits significantly:
- Efficiency: With AeroPoints, you don’t have to manually shoot and mark GCPs or worry about re-shooting them as your site changes.
- Ease of use: Simply place an AeroPoint within your flight area before take-off and activate with a single button. When your drone survey is complete, pick up the AeroPoint and allow it to connect to WiFi. Once it’s locked on a signal, it will auto-upload its data to Propeller.
- Cost savings: Optimize labor by saving hours that would have been spent walking a site and manually marking GCPs.
- Safety: Walking a worksite can be dangerous; using AeroPoints keeps workers safe by keeping their boots on solid ground.
