GSD calculator: ground sample distance, overlap and photo spacing
Work out ground sample distance, photo footprint, line spacing, camera interval and photos per hectare or acre for a drone mapping flight, from the camera, the height, the overlap and the speed.
Published · 3 min read · By Malya, the makers of Clarity
Plan a mapping flight from the numbers that matter: how much ground one pixel covers, how far apart the photos and the flight lines are, how often the camera has to fire, and how many photos the job will take. Pick a camera, set the height and the overlap, and the results update as you type, in metres or feet.
GSD and overlap calculator
- Ground sample distance
- 2.66 cm/px
- Photo footprint
- 140.7 m × 105.4 m
- Photos per hectare
- 11
- Distance between photos
- 21.1 m
- Distance between lines
- 42.2 m
- Camera interval at that speed
- 2.6 s
GSD = sensor width × height ÷ (focal length × image width). Footprint is GSD × pixels; spacing is footprint × (1 − overlap). Most mapping drones cannot fire faster than about every 2 s; if the interval comes out below that, slow down or fly higher.
What the numbers mean
- Ground sample distance is the pixel on the ground. It decides the finest detail the map can show, and with good positioning the map is accurate to about one to three times it.
- Photo footprint is the ground one photo covers, across and along the flight line.
- Distance between photos and between lines come from the footprint and the overlaps: 80% front overlap means each photo moves on by a fifth of its footprint.
- Camera interval is the time between photos at your speed. Most mapping cameras need about two seconds between frames; below that, slow down or fly higher.
- Photos per hectare or acre scales the job: multiply by the site area for the photo count, which drives both the time in the air and the time to process.
| Height | GSD | Photos per hectare | Photos per acre |
|---|---|---|---|
| 60 m (200 ft) | 1.6 cm/px (0.63 in) | about 31 | about 13 |
| 80 m (260 ft) | 2.1 cm/px (0.84 in) | about 18 | about 7 |
| 100 m (330 ft) | 2.7 cm/px (1.05 in) | about 11 | about 5 |
| 120 m (400 ft) | 3.2 cm/px (1.26 in) | about 8 | about 3 |
From the numbers to a flight that processes
The calculator gives the geometry. Whether the flight processes into a clean map also depends on the overlap suited to the ground, the light, shutter speed and positioning: all of it is in how to fly a drone for photogrammetry. What accuracy each kind of positioning gives, in centimetres, is in drone survey accuracy. When the photos are in, Clarity's processing turns them into the orthomosaic and terrain model and reports the GSD it actually achieved.
Questions people ask
What is GSD?
Ground sample distance: the width of ground covered by one pixel of the photo, usually given in centimetres or inches per pixel. A GSD of 2.5 cm means each pixel shows a 2.5 cm square of ground. It is set by the camera's sensor, the lens and the height above ground, and it limits the detail and the accuracy of the finished map.
How do you calculate ground sample distance?
GSD = sensor width × flying height ÷ (focal length × image width in pixels). With the sensor width and focal length in millimetres and the height in metres, multiply by 100 to get centimetres per pixel. A 17.3 mm sensor, 12.3 mm lens and 5,280-pixel image at 100 m gives 2.66 cm per pixel.
What GSD do I need for a construction survey?
For volumes and earthwork, 2 to 3 cm per pixel is the usual target, which a 20 MP mapping drone gives at 75 to 110 m. Finer than 2 cm costs flight time and photos for little extra accuracy unless the job needs fine detail; coarser than 5 cm starts to blur the edges of piles, kerbs and batters.
Is a smaller GSD always more accurate?
It is more detailed, and accuracy is usually one to three times the GSD, so up to a point it helps. But the accuracy of where the map sits on the earth comes from ground control, RTK or PPK, not from pixel size. A 1 cm map without positioning can still be a metre out.
Do it in Clarity.
Explore is free, with no card and no expiry: a real quarry, already flown, to try every tool on. Studio is $50 a month for up to five sites of your own ground, from the orthomosaic and terrain model you already have. Enterprise processes your photos.
Read next
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- Construction progress monitoring with drones: tracking and reportingWhat a flight measures that a site walk cannot, how often to fly, and what goes in the monthly report.
- Construction punch lists and field quality observationsWhat each record needs, a workflow from raised to closed, when an observation becomes an NCR, and the numbers worth watching.
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