Ground Sampling Distance
The size in real-world units (typically cm/px) represented by one pixel in a drone or aerial image — the primary metric for spatial resolution in drone survey.
Ground Sampling Distance (GSD) is the size of one pixel in a drone or aerial photograph, expressed in real-world units — typically centimetres per pixel (cm/px). A GSD of 2 cm/px means each pixel in the image corresponds to a 2 cm × 2 cm area on the ground.
GSD determines the spatial resolution of drone photogrammetry output. Smaller GSD means higher resolution and more detail captured, but requires flying lower or using a camera with higher pixel count. For heritage condition assessment and architectural documentation, a GSD of 1–2 cm/px is typically adequate. For fine sculptural detail, a GSD of 5 mm or better is needed.
GSD is related to flight altitude by a simple formula: GSD = (sensor width in mm × altitude in m) ÷ (focal length in mm × image width in pixels). Drone manufacturers and photogrammetry software calculate this automatically for mission planning.