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Preparing ground control points for PPK UAV mapping

This tutorial shows how to prepare ground control points for precise PPK UAV mapping.


Check the How PPK works and Configuring Reach UAV kit for PPK mapping guides to learn more.


Ground control points (GCPs) are points with known coordinates on the ground in the survey area that serve as reference points and help accurately map areas.

Use ground control points for any of the following purposes:

  • To check and improve the accuracy of the map.
  • To get the correct scale and orientation of the map.
  • To ensure absolute positioning of the map.

Learn more about absolute and relative accuracy and positioning in the Choosing base setup method article.


To ensure precise drone mapping, you need to place and collect GCPs in RTK mode in the survey area.


In most cases, GCPs are necessary to obtain absolute accuracy and georeference the map. In this case, you should place the base over a known point and manually enter its coordinates. To learn more, check the Choosing base setup method guide.

Placing GCPs

When placing GCPs, follow the requirements below:

  • Make your GCPs clearly visible on the drone’s images: they should be big enough and contrast with the surroundings.
  • Provide enough GCPs depending on the survey area. Usually, you need 5–10 points.
  • Place GCPs evenly in the survey area. For example, if you use 5 points, set one for each corner and the last one in the center of the area.

To ensure good area cover, avoid placing GCPs in single straight lines.

  • Try to place GCPs at the highest and lowest points on the site. It will help perform the correct flat projection.

Measuring GCPs

After placing GCPs, you need to collect them. Follow the steps below.

Configuring Reach RS2/RS2+

First, you need to configure your Reach RS2/RS2+ to receive RTK corrections. You can do it in the following ways:

  • Working with RS2/RS2+ base
  • Working with NTRIP service

Collecting GCPs

To collect points using Emlid Flow, follow the steps below.

  1. Go to the Survey tab and create a project.


    To learn more, check the How to create a project guide.

  2. Collect your ground control points.


    To learn more, check the Collect points guide.

  3. Export the project once you collected GCPs.


    To learn more, check the Export projects guide.

Now the list of your points is ready for import to photogrammetry software.

Further reading