Ground sample distance (GSD) is the distance on the ground between the centres of two neighbouring pixels in an aerial image – in other words, the real-world size of one pixel. A GSD of 2 cm/px means every pixel represents a 2 × 2 cm patch, so features smaller than a few centimetres cannot be resolved. It is the key quality figure for drone mapping, photogrammetry, orthomosaics and surveying.
GSD follows from similar triangles: the sensor sees the ground through the lens, so the ground width covered by the image is the sensor width multiplied by altitude ÷ focal length, and dividing by the number of pixels across gives the size of one pixel. Flying twice as high doubles the GSD (coarser detail) but covers four times the area per photo, so mapping jobs trade detail against flight time and battery count.
Always use the real focal length of the lens, not the 35 mm equivalent printed in marketing material, and the physical sensor width in millimetres. The calculator also gives the footprint of each image and, for a planned overlap, the distance between photos along a flight line and between flight lines – 70–80% overlap is typical for photogrammetry.
How to use the Ground Sample Distance Calculator
- Calculate
- Sensor width
- Sensor height
- Focal length (real, not 35 mm equivalent)
- Image width
- Image height
- Flight altitude above ground
- Target GSD
- Image overlap (front and side)
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Choose whether to find the GSD or the altitude, enter the camera’s sensor size, real focal length and image size in pixels, and the altitude or target GSD. The calculator applies the similar-triangle formula and multiplies GSD by the pixel counts for the footprint.
Worked example
A drone with a 13.2 × 8.8 mm sensor, an 8.8 mm lens and 5,472 × 3,648 px images flies at 100 m. GSD = 13.2 × 100 ÷ (8.8 × 5,472) = 0.0274 m = 2.74 cm/px. Each photo covers 150 × 100 m (1.5 ha). With 75% overlap the drone triggers every 25 m and flight lines are 37.5 m apart. For a 2 cm/px target the same camera must fly at 2 × 8.8 × 5,472 ÷ 13.2 cm = 73 m.
GSD and altitude for this camera
| Altitude | GSD | Footprint |
|---|---|---|
| 30 m | 0.82 cm/px | 45 × 30 m |
| 60 m | 1.64 cm/px | 90 × 60 m |
| 100 m | 2.74 cm/px | 150 × 100 m |
| 120 m | 3.29 cm/px | 180 × 120 m |
Inputs explained
| Field | What to enter |
|---|---|
| Calculate | Choose one: Ground sample distance from altitude, Flight altitude for a target GSD |
| Sensor width | Units: mm, cm, in |
| Sensor height | Units: mm, cm, in |
| Focal length (real, not 35 mm equivalent) | Units: mm, cm, in |
| Image width | In px |
| Image height | In px |
| Flight altitude above ground | Units: m, ft |
| Target GSD | Units: cm/px, mm/px, in/px, m/px |
| Image overlap (front and side) | In % |
What each result means
- Footprint width on the ground = [Ground sample distance]×[Image width]
- Footprint height on the ground = [Ground sample distance]×[Image height]
- Area covered by one image = [Footprint width on the ground]×[Footprint height on the ground]
- Distance between photos along a flight line = [Footprint height on the ground]×(1 – [Image overlap (front and side)]÷100)
- Distance between flight lines = [Footprint width on the ground]×(1 – [Image overlap (front and side)]÷100)
Formula
GSD = (sensor width × altitude) ÷ (focal length × image width in pixels) · altitude = GSD × focal length × image width ÷ sensor width · footprint = GSD × pixels
Worked example
Inputs — Calculate: Ground sample distance from altitude; Sensor width: 13.2 mm; Sensor height: 8.8 mm; Focal length (real, not 35 mm equivalent): 8.8 mm; Image width: 5,472 px; Image height: 3,648 px; Flight altitude above ground: 100 m; Image overlap (front and side): 75 %.
Results — Ground sample distance = 2.7412 cm/px; Flight altitude = 100 m; Footprint width on the ground = 150 m; Footprint height on the ground = 100 m; Area covered by one image = 15,000 m²; Distance between photos along a flight line = 25 m; Distance between flight lines = 37.5 m.
Key terms
- Ground sample distance
- Ground distance represented by one pixel.
- Footprint
- Area of ground covered by one image.
- Front overlap
- Overlap between consecutive photos along a flight line.
- Side overlap
- Overlap between photos on neighbouring flight lines.
Frequently asked questions
What is a good GSD for drone mapping?
1–3 cm/px for construction, inspection and surveying; 5–10 cm/px for agriculture and large-area mapping.
How do I get a smaller GSD?
Fly lower, use a longer focal length or a camera with more pixels across the same sensor width.
What is the GSD of a DJI Phantom 4 Pro at 100 m?
About 2.74 cm/px (13.2 mm sensor, 8.8 mm lens, 5,472 px wide).
Does GSD equal accuracy?
No – survey accuracy is typically 1–3 times the GSD and depends on ground control points and processing.
Why use the real focal length?
GSD depends on the actual lens geometry; a "24 mm equivalent" lens on a 1-inch sensor is really about 8.8 mm.
Is GSD the same across the image?
Only for a level camera over flat ground; terrain and tilt change it locally.