How Many AeroPoints and Ground Control Points Do I Need for My Survey?

We are often asked, “How many AeroPoints do I need for my survey?” This is a difficult question to answer as it relies on a number of factors, including:

  • What drone and camera you’re using,
  • Whether or not the drone is RTK or PPK capable,
  • The physical terrain of your site (i.e., is it hilly? Is it flat?), 
  • The size of your site.

Similar to traditional ground control, the more AeroPoints you use, the better results you'll get. AeroPoints work collaboratively to correct against each other, so the accuracy of each unit increases when more AeroPoints are laid out.

There are a number of factors that can contribute to an accurate (or inaccurate) survey.  This article will help arm you with the knowledge required to confidently lay out your AeroPoints and be confident that you will be generating an accurate survey every time.

Non-PPK/RTK capable drones

For a drone that is not PPK or RTK capable, you will need AeroPoints (or ground control points) within your survey area to ensure that the model is accurate. Ground control points (GCPs) tie the model produced by your imagery to known points in the real world. 

During the photogrammetry process, the images taken by your drone are stitched together to produce a digital elevation model (DEM) and an orthomosaic. However, when your drone takes an image, it only knows where it is in the sky within a margin of error of around 10 meters. Although you can still produce a DEM, without ground control, your model will warp and bend.

Think of your site like a tarp on a windy day. You need stakes (i.e., AeroPoints or other GCPs) to keep the tarp (accuracy) from blowing away. If your tarp lacks enough stakes, it will be blown about in the wind. In order to stop this from happening, we recommend that you use at least five GCPs.  

Check out our article Best practices for ground control placement in the Knowledge Base to learn more.

The number of GCPs you need is also dependent on how high you are flying and how your site varies in elevation. As a general rule, the GCPs should be spaced in an even grid-like pattern across the site with the following considerations:

  • The spacing between ground control points should be approximately twice your flight height. For example, if you are flying at 100 meters (~330 ft) your control should be placed in a grid with 200 meters (~660ft) spacings. 
  • Capture all high and low points if safe to do so.
  • The ground control creates the ‘boundary of accuracy’ for the survey. Anything outside the boundary the ground control points created should be considered inaccurate. 
  • A minimum of five GCPs. (AeroPoints and/or custom GCPs can be used together).
The following diagram gives a representation of both bad and good GCP placement. You can see in the red image that the site is either under-constrained or the high and/or low points are not covered.

PPK/RTK capable drones

For a PPK or RTK capable drone, the requirement for ground control is less than that of ‘normal’ accuracy drones. However, ground control is still necessary. 

I still can't do it!

We wrote these articles to equip you with everything you need to get the job done on your own, but we understand that sometimes this isn't sufficient.

If you're stuck, you can connect with our support team by clicking the support button on the top right corner of your user portal.

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