Ground control points

Ground control points are designated locations on a job site that have been precisely measured using Real Time Kinematic (RTK) GPS coordinates. Ground control points, often referred to as GCPs, are used extensively in drone surveying and construction to increase the accuracy of drone maps.

Site Scan smart GCP tagging

Tagging ground control points in Site Scan

In photogrammetry, ground control points are used to georeference the photos taken by a drone or another sensor, ensuring that when the images are stitched together into an orthomosaic, the ground control points are properly aligned. In this vein, more ground control points used generally correlates with higher accuracy. That said, drone mapping software like Site Scan can achieve accuracy within 1/10th of an inch with the use of a minimum of 4 ground control points, spaced appropriately across the survey site.

Ground control points must be visually distinct from their surroundings in order to be easily spotted by manual tagging efforts or automated ground control point detection software. This is often achieved by using high contrast markings and distinct shapes. Often, a spray painted orange or white X, or a black and white checkered pattern are used. Depending on the altitude of a drone survey flight, a ground control point should be of a large enough size to appear clearly in photographs.

Once ground control points are placed, an RTK GPS system, such as a total station or more cost effective alternative, such as Trimble-enabled 3DR GCP, should be used to capture the exact GPS coordinates of the ground control point.

Collecting ground control points and automatically uploading them to the cloud with 3DR GCP.

Finally, you can survey your site using a drone, and once uploading of photos has finished, you can begin the process of tagging ground control points in your photographs to ensure accuracy. Drone mapping software like Site Scan has streamlined this otherwise tedious process with automated ground control point detection, which allows you to quickly and easily confirm or reject the ground control points in your photographs that the software has detected.

After the tagging is completed, the georeferenced orthomosaic is ready to be processed, and you can see the resulting product and accuracy.


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