How to Set Ground Control Points for Greater Accuracy in UAV Mapping

Drone U
Drone U
Jul 31, 2018 · 4 min read

What Are Ground Control Points? And, Their Role in UAV Mapping….

If you are a part of the UAV mapping industry, you must be aware of Ground Control Points (GCP’s). Ground Control Points can help you create more accurate drone maps.

There are different kind of GPS available, each with varying accuracy. For creating Ground Control Points, you need to use RTK — GPS or PPK — GPS. RTK GPS or Real Time Kinematics can help you create drone maps with an accuracy level of 2 cm to 6 cm. Whereas PPK GPS or Post Processing Kinematics is even more accurate, and you can expect mm grade accuracy in UAV mapping.

Collecting good GPS data is really difficult. And this is because of earth’s uneven surface which can be likened to a piece of crumpled paper. This makes collecting good elevation data particularly difficult. Particularly, if you need a survey team to sign off on your drone model, they will not do so unless you use GCP’s.


Will Using Propeller Aeropoints Help You Arrive at Survey Grade Accuracy in UAV Mapping?

There are different ways via which drone pilots can set Ground Control Points. One of the most popular ways is by using “Smart GCP’s” called Propeller Aeropoints. Propeller Aeropoints are 2 foot squares which can turned on with a click of a button. These GCP’s which will work with any GPS enabled drone.

Propeller Aeropoints are equipped with RTK-GPS whereas popular commercial drones like the Phantom 4 have the GLONASS system. In order for GCP’s to work, they need to be equipped with a more sophisticated GPS system compared to the drone.

Aeropoints work with popular UAV mapping applications like Pix4D and PhotoScan. Data is automatically uploaded to Propeller’s platform, and you can access the processed data via Propeller’s web based platform in 24 hours.

The main disadvantage of using Propeller Aeropoints is the huge initial investment. Because these GCP’s only come in sets of 10, opting for these will set you back by a hefty 6 grand. Another factor worth noting is that you can only avail a year of free processing on buying these GCP’s. After a year, you will have to fork out a processing cost too.

Of course, in order to limit your investment, you can get in touch with your friends or peers and split the cost of these GCP’s. But, don’t you need multiple smart GCP’s for creating a drone map? Not really. In fact you need just one Propeller GCP for determining the exact GPS location. Once you have determined the location, you can replace the Propeller GCP by a “Fake GCP”, thus creating a point of reference. A fake GCP is nothing but a black and white plywood cut out measuring 2 feet x 2 feet. Check out our construction mapping course where Drone U Elite member and course Instructor, PJ KirkPatrick shows you how build a fake GCP for just 50 bucks!


Are There Better Options for Setting GCP’s for Accurate UAV Mapping? We Discuss Reach RS and Trimble….

Reach RS by Emlid is a good alternative to Propeller Aeropoints. Reach RS is a RTK GNSS receiver that can be controlled via an app on your smartphone. The Reach RS receiver should be mounted on a tripod.

So, how does Reach RS compare to Propeller Aeropoints? The first advantage of using Reach RS to set GCP’s is the lower upfront investment. The Reach RS costs $799, and you can make do with just one unit. Also, unlike Aeropoints, Reach RS comes with unlimited processing.

Because the Reach RS unit is mounted on a tripod, there will be less signal obstruction — which will result in greater accuracy. Using the Reach RS will give you 7 mm horizontal accuracy and 13 mm vertical accuracy. Do not forget to correct for height if you are using fake GCP’s.

Apart from Propeller Aeropoints and Reach RS, using a Trimble unit is an option, albeit an expensive one. The cost of a Trimble unit is $15,000 and upwards. Trimble RTK units are normally used on construction sites for surveying purposes.


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