Ground control points (GCP) are points, or features, that you can identify clearly in the raw image for which you have a known ground coordinate. GCPs can come from a variety of sources, such as the Global Positioning System (GPS), ground surveys, geocoded images, vectors, geographic information systems (GIS), topographic maps, chip databases, or by using photogrammetric processes to extend the number of GCPs in your images.
A GCP determines the relationship between the raw image and the ground by associating the pixel (P) and line (L) image coordinates to the x, y, and z coordinates on the ground.
GCPs are often required in a photogrammetric process: you can model the location, or position, and the orientation of the sensor at the time that the image was acquired, through a rigorous modeling process. While most sensors come with a preliminary model, these models are often not accurate enough to meet project specifications. By using GCPs, you can refine the model such that it meets your project requirements.
© PCI Geomatics Enterprises, Inc.®, 2026. All rights reserved.