Cameras and sensors for photogrammetry: what matters in the spec sheet
Sensor size, megapixels, global against rolling shutter, lenses and focal length, calibration, and the multispectral and thermal sensors that fly beside the camera: what each means for the model.
Published · 9 min read · By Malya, the makers of Clarity
The camera is the instrument. Everything a photogrammetry survey can measure is in the pixels it recorded, and nothing in processing adds detail that was not there. The spec sheet has a dozen numbers on it and four of them matter: sensor size, shutter type, lens and, a distant fourth, megapixels. This page reads the sheet in that order.
The pixel: sensor, lens, height
Similar triangles
G / H = s / f
GSD = G / pixels across
= (s × H) / (f × pixels)
A 1-inch sensor 13.2 mm wide with 5,472 pixels across, behind an 8.8 mm lens, 100 m up:
13.2 × 100 ÷ (8.8 × 5472) = 2.7 cm
Halve the height and the pixel halves. A longer lens does the same from the same height, at the cost of a narrower picture and more of them.
Two similar triangles set the ground sample distance: the sensor over the focal length, the ground over the flying height. A wider sensor sees more ground; a longer lens sees less of it, bigger; a lower flight makes every pixel smaller. The GSD calculator does the arithmetic for any camera and height, and the 101 turns it into a flight plan.
Sensor size and megapixels
Megapixels say how many pixels; sensor size says how good each one is. A larger sensor has larger pixels that gather more light, so the picture is sharper in shade, cleaner at the exposure a fast shutter needs, and richer in the fine texture the matcher feeds on. It also sees more ground for the same lens. The practical tiers:
| Sensor | Typical camera | Pixel at 100 m | |
|---|---|---|---|
| Phone, 1/2-inch class | 12–48 MP phone; small consumer drones | 3–4 cm (and a rolling shutter) | |
| 1-inch, 20 MP | The standard mapping-drone camera for a decade | 2.7 cm with a 24 mm-equivalent lens | |
| 4/3, 20 MP | Mid-range survey drones; mechanical shutter | 2.5–3 cm, cleaner than 1-inch | |
| APS-C, 24–26 MP | Mirrorless cameras on larger drones; close-range work | 1.5–2.5 cm depending on lens | |
| Full frame, 45–60 MP | Survey payloads; the best close-range work | 1–1.5 cm with a 35 mm lens; 3 km² a flight at a coarser pixel |
Past 20 MP, more pixels mostly buy a choice: fly higher for the same pixel and cover more ground, or fly the same height for a finer one. They do not buy accuracy on their own; the accuracy page shows that control and geometry decide that.
Shutter: global, mechanical, rolling
A global shutter exposes every pixel at the same instant. A mechanical shutter does the same in effect: a physical curtain exposes the whole sensor in a few milliseconds. A rolling shutter reads the sensor a row at a time over tens of milliseconds, and from a moving drone each row sees the ground from a different place, so straight edges lean and the solver is handed a camera model that is wrong by an amount that changes with speed. One study of three processing packages found the error could not be removed by adding control points; it had to be modelled.
If the camera is rolling shutter
- Fly slowly: the lean is speed × readout time
- Use software that models rolling shutter, and give it the readout time
- Fly higher rather than lower when the pixel allows: the shift is a smaller fraction of the footprint
- Keep the camera still for each shot in close-range work
If you are choosing a camera
- A mechanical or global shutter is worth more than any number of megapixels
- Check the readout time if it is rolling; under 20 ms is workable, over 40 ms is not for mapping
- A fast shutter speed (1/1000 s or faster) is needed either way to freeze the ground
Lens and calibration
The solver needs to know the lens: its focal length, where its optical centre falls on the sensor, and how it bends straight lines towards the edges of the frame (radial distortion, strongest on wide lenses). It can estimate all of these from the photographs themselves, which works well on a block with oblique lines and poorly on a flat nadir-only block where a lens error and a curved world look alike. A stored calibration, made from a good block or a calibration target, can be held fixed in the solution instead.
- Focal length
- 24–35 mm full-frame equivalent for mapping: enough footprint, modest distortion. Longer for a finer pixel from height; never a zoom.
- Fixed focus
- Set at infinity (or the subject distance) and locked. A lens that refocused between lines is two lenses to the solver.
- Distortion
- Modelled, not avoided. Fisheye lenses can be used with the right model but give the solver more to estimate.
- Stability
- A rigid mount. A camera that shifts against its mount between photographs defeats any calibration.
Settings that make or break a survey
The same camera gives a good survey or a poor one depending on four settings, all of which should be set once and left alone for the whole flight.
- Shutter speed
- 1/1000 s or faster from a moving drone, so the ground is not smeared across a pixel.
- Aperture
- f/4–f/8: sharp across the frame without diffraction softening it. Let ISO take the strain.
- Exposure
- Manual, or locked. Automatic exposure makes neighbouring photographs of the same ground differ, and the matcher notices.
- Format
- JPEG at the highest quality is fine and small; RAW gives latitude for shadowed pits at the cost of storage and processing time.
Beyond the ordinary camera
- Oblique rigsThree or five cameras angled at once: nadir plus the four sides. City models and façades in one flight, at the cost of five times the pictures.
- MultispectralSeveral narrow bands (red edge, near infrared) for crop vigour, water and soil. Low resolution, draped over the ordinary camera's geometry.
- ThermalHeat, at a few hundred pixels across. Roof leaks, solar panels, pipes, wildlife at night. Mapped by photogrammetry on the thermal images or on a paired visible camera.
And the companion that is not a camera at all: LiDAR, which measures distance directly and is flown beside a camera for the ground under trees. The scanners page has it.
Choosing one
| For | Look for | Because | |
|---|---|---|---|
| Site surveys on a budget | 1-inch, 20 MP, in a mapping drone with a mechanical shutter if possible | A 2–3 cm pixel from 100 m, and a shutter that does not lean | |
| Site surveys to a stated accuracy | 4/3 or full-frame, 20–45 MP, mechanical shutter, RTK drone | Cleaner pixels, more ground per flight, and positions for every photograph | |
| Façades, plant, close-range | Mirrorless APS-C or full-frame, a 24–35 mm prime, flash with polarisers | Sub-centimetre pixels, stable lens, controlled light | |
| Objects on a table | Any camera, even a phone, on a tripod | Stillness and even light matter more than the sensor | |
| Crops and water | Multispectral alongside an ordinary camera | Bands the eye cannot see, on geometry the ordinary camera provides |
Sources
Questions people ask
How many megapixels do I need for photogrammetry?
Fewer than the brochure says. 20 MP on a 1-inch sensor is the usual floor for survey work and gives a 2–3 cm pixel from 100 m; 45 MP full-frame roughly halves the pixel or doubles the area per flight. Past that, sensor size, lens quality and shutter matter far more than pixel count.
Global or rolling shutter?
Global if you can: every pixel exposed at the same instant, so a moving drone does not lean the picture. Most small cameras are rolling shutter, which is workable if the readout is fast, the drone flies slowly enough, and the software models it. Mechanical shutters on larger cameras are global in effect.
What focal length is best?
A moderate wide angle: about 24–35 mm full-frame equivalent. Wider lenses distort more at the edges and the solver has to model it; longer lenses give a finer pixel from the same height but a narrower footprint, so more photographs. Fixed, never zoom.
Does camera calibration matter?
Yes. The solver needs the lens's focal length, centre and distortion. It can self-calibrate from a well-flown block with obliques, or use a stored calibration, which is safer on nadir-only flights where doming can otherwise hide a lens error. Never change focus or zoom during a survey.
Can I use a multispectral or thermal camera for photogrammetry?
Yes, with the same method and lower resolution. Multispectral cameras map crop and water condition; thermal cameras map heat on roofs, pipes and panels. They are usually flown beside an ordinary camera, which gives the sharp geometry the others are draped over.
See it on a real site.
Explore is free, with no card and no expiry: a real quarry, already flown and processed, with every measuring tool on it.
Read next
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- Photogrammetry equipment: everything you need, from phone to droneThe kit, from a phone and a scale bar to an RTK drone and a scanning robot, and what each buys you.
- Drones for photogrammetry: multirotor, fixed-wing and VTOLMultirotor, fixed-wing or VTOL, with or without RTK: which drone maps which site.
- All resources