GCPs vs RTK vs PPK - What is best?
There are many different ways of improving your data collection and delivery in the drone industry, from the type of camera you use to the actual drone itself, but there are 3 tried and tested methods that can vastly improve the accuracy and quality of the data you collect.
As the title suggests this post will concentrate on GCPs, RTK, and PPK and which method is best to improve not only the quality of your data but the accuracy.
In this post, we will be looking at the advantages and disadvantages of each to help you make a choice of what option you think is best.
GCPs, short for Ground Control Points are points that are laid out on the ground that have known coordinates.
A GCP is often a square of chequered fabric, as shown above, that is laid down across
the site at various designated spots. These markers act as a known coordinate point.
How do they work? 💡
markers are placed on the ground
measure their position using survey-grade equipment, like a base station
upload those positions alongside the images to the processing software
doesn’t require RTK-enabled drones
a relatively low-cost upfront investment
good fallback method if nothing else works
requires instrumenting the site - the survey might take longer
requires access to different parts of the site
RTK stands for Real-Time Kinematic and is a technique used to increase the accuracy of GNSS (global navigation satellite system) positions using a fixed base station that remotely sends out data to a moving receiver.
DJI has developed drones that carry an RTK unit, these RTK units can be found on the DJI M300, DJI M2E, Phantom 4 RTK, and most recently the DJI M3E.
How does it work? 💡
drone positions itself using a base station and satellite
real-time corrections for GPS positions
no post-processing needed
drone positioning is precise - increases safety
less time on site and post-processing
at the mercy of signal in the field
requires a base station or internet connection
nothing to fall back on if you lose connection during the flight
PPK stands for Post Processed Kinematic and is a method of correcting the data after the flight has taken place and the data has been uploaded.
The data can be uploaded to specialist software that enables the correction of data after the flight has occurred, hence Post Processed.
How does it work? 💡
requires RTK devices to log their own position separately
positions are corrected in the post using software
allows for many corrections in the post including lever arm correction
doesn’t need instrumenting the site or constant connection
easier to correct positions in the comfort of an office
doesn’t provide real-time corrections for safety
requires additional post-processing software
not a real-time method - still requires RTK-enabled hardware
How To Decide
So now we have looked at all the advantages and disadvantages of the three options how do you decide on what method is best?
There are a few factors to consider...
do you have site access?
what’s your budget?
how much time do you want to spend on-site vs in the office?
Can you invest in additional software?
Our recommendation would be geared more toward the use of GCPs with post-processing your data using PPK for most projects, and RTK for projects that involve open spaces so that signal strength is not an issue.
For more information on some of our subjects above please see the following posts:
How to Collect High-Quality Data for Photogrammetry
How to Achieve Highly Accurate Flights Using RTK
We hope this blog post helps you understand which method is best, GCPs, RTK, or PPK?
If you'd like to learn more about how to high-quality data and get the most out of your drone missions, please feel free to visit our learning resources.
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— Team at Hammer Missions
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