Ground control point, a marked feature on the earth's surface with known exact coordinates used to anchor aerial mapping and photogrammetry. Surveyors set targets on the ground and measure their positions with GNSS receivers so that drone software or satellite imagery can tie the pixels to real-world coordinates. Without them, aerial models float in an arbitrary coordinate system and lack absolute accuracy.
Heard on the job
Make sure you paint the GCP targets large enough for the drone to pick them up at 400 feet.