Drone payload camera selection for inspection and mapping

A drone payload camera is not chosen by megapixel count. You choose it backwards from the smallest detail you must see from the air: set the ground sample distance, derive the focal length, then filter cameras and lenses by what survives flight — global shutter for motion, a low-latency feed for the pilot, grams on the mass budget, and a housing that keeps out rain. This guide is for engineers specifying inspection payloads for bridges, façades, tank farms and power lines, and mapping payloads for photogrammetry. You will work one example end to end — resolving a 5 mm crack from 50 m altitude — with the focal length it demands, the exposure it allows at cruise speed, the storage it writes and the shutter it needs.

Size the ground sample distance first

Ground sample distance (GSD) is the ground area one pixel covers, and it decides what the payload can detect. A feature needs about two pixels across it before you can measure it rather than just see it, so the smallest target sets the GSD, and the GSD sets everything else:

Keep altitude and sensor width in the same unit and GSD comes out per pixel in that unit. Sensor widths follow the standard optical-format sizes: a 1/1.7-inch type sensor is about 7.4 mm wide with a 9.3 mm diagonal, 2/3-inch about 8.8 mm, 1-inch 12.8 mm, and 1.1-inch about 14.1 mm wide. Multiplying the nominal inch figure by 16 mm estimates the diagonal of any format.

Every input moves GSD linearly. Double the altitude and the GSD doubles; double the focal length and it halves. A nadir view — camera straight down — is the honest case: tilt 45° off vertical and the footprint stretches by 1/cos(45°) ≈ 1.4 along the tilt, so a crack crosses fewer pixels than the nadir math promised. The two-pixel basis is the same sizing rule used for ground-based defect work, set out in camera resolution for defect detection.

Worked example: a 5 mm crack at 50 m

Four steps, with the arithmetic.

1. Set the GSD target. Smallest feature 5 mm, two pixels across: 5 mm ÷ 2 = 2.5 mm/px.
2. Pick the sensor. A 4000 × 3000 array in 1/1.7" format (7.4 mm wide) is a standard industrial part: the LS-CMR-0166 runs it at 30 fps over USB3, the LS-CMR-0053 at 9 fps over GigE. Required footprint: 4000 px × 2.5 mm/px = 10.0 m wide.
3. Solve the focal length. f = 50 m × 7.4 mm ÷ 10 m = 37 mm.
4. Choose the nearest standard lens and read the margin.

Decision: take the 50 mm lens — 2.7 pixels on the crack, with margin for tilt and timing. The 40 mm suits you when coverage area matters more than margin; the 35 mm sits just under the rule and the 25 mm fails it.

The same target on the larger global-shutter format: the standard 1.1-inch 12 MP array is 4096 × 3000 pixels across about 14.1 mm. Required footprint: 4096 px × 2.5 mm/px = 10.24 m, so f = 50 × 14.1 ÷ 10.24 ≈ 69 mm, and the 75 mm class lands at 2.3 mm/px with 2.2 pixels on the crack. Bigger pixels buy shutter speed and light; the focal length grows with the sensor.

Motion blur sets the exposure cap

Blur stays under one pixel when exposure ≤ GSD ÷ ground speed. At 1.85 mm/px and a 2 m/s cruise: 1.85 mm ÷ 2000 mm/s = 0.9 ms. Halve the speed and you double the allowance; a hover with 0.5 m/s of sway allows 3.7 ms. Full sun gives a mono industrial camera usable signal in 1-2 ms at mid f-numbers; under overcast skies the honest moves are flying slower, lower, or both.

The flight plan follows from the footprint

At 50 mm the footprint is 7.4 × 5.6 m — 5.6 m from the 5.58 mm sensor height. Typical photogrammetry practice plans 75% forward and 65% sidelap. Forward advance per frame: 5.6 m × (1 − 0.75) = 1.4 m, which is one frame every 0.7 s at 2 m/s, about 1.4 frames per second. Line spacing: 7.4 m × (1 − 0.65) = 2.6 m, so coverage runs at 2 m/s × 2.6 m = 5.2 m²/s ≈ 1.9 ha per hour. Storage: a 4000 × 3000 8-bit mono frame is 12 MB, so 1.4 frames per second writes about 62 GB per flight hour; 12-bit raises that to about 93 GB.

Shutter: global on anything that moves

A rolling shutter reads the rows in sequence, and a 12 MP rolling readout spans roughly 25-30 ms. At 2 m/s the platform moves 50-60 mm during the readout, so every frame arrives skewed — photogrammetry software will still register the images, but the geometry inherits the error.

Global shutter exposes all rows at once and freezes the geometry. Decision: line-flight mapping and any inspection flown on a path — global shutter, always. A static hover with exposures held under a few milliseconds can live with rolling.

For the mapping role the shortlist starts at the 12 MP global-shutter class:

When you can fly lower, the MV-CU020-90GC — 2.5 MP, 1/1.7" format, global shutter, GigE — is the lighter sibling; fewer pixels per crack is exactly the trade. The full argument is set out in global vs rolling shutter sensors.

Latency: budget the pilot link separately

Glass-to-glass latency is the time from photons at the lens to pixels on the pilot's screen. Published FPV tests measure complete 720p chains under 50 ms, with camera-side chains under 10 ms; treat 50 ms as the working budget for confident manual flight near structures. A compressed mapping stream commonly adds 100 ms or more once encoder and network buffering stack up, so pilot from a separate raw feed or not at all.

Machine-vision parts serve the pilot path well: raw USB3 or GigE frames into the onboard computer, no compression in the loop, short exposure, high frame rate. At 120 fps the frame period is 8.3 ms, well inside the budget, and a 0.9 ms exposure adds almost nothing to it. Subsampled or binned readouts trade resolution for frame rate where the pilot feed does not need mapping detail — the trade is worked through in 4x4 binning vs 2x2. For tethered platforms, GigE carries its standard 100 m run to a ground computer.

Weight, power and the mass spiral

Mass is the payload currency. Typical classes: a bare board module lands in the tens of grams with an M12 lens at a few grams more; a cased industrial camera with a C-mount FA lens reaches hundreds of grams. Cables and the housing window add tens of grams of their own. Power draw runs about 2-4 W per camera before the interface and compute. On a small quad, a working rule of thumb is roughly a minute of hover per 100 g — scale the exact figure from your platform's thrust data.

For pilot and trigger duty, weigh the light global-shutter modules first:

Decision: the smaller the platform, the more the bare-board route pays. The cased camera pays back in connectors, mounting and shielding once the platform stops caring about tens of grams.

Lenses: cover the sensor, resolve the pixels, hold the focus

Three checks, in order. First, image circle: the lens circle must exceed the sensor diagonal — a 1/1.7-inch sensor needs at least 9.3 mm, which a 2/3-inch lens (11 mm) covers. Second, rating: 7.4 mm across 4000 pixels is 1.85 µm per pixel, and a lens rated below the sensor's megapixel class will soften exactly the detail you flew to collect; pick a 12 MP-class lens for a 12 MP sensor. Third, distortion: photogrammetry wants under 0.3%, which is what the LS-FFL-0567 prints — 16 mm, 1.1" format, 20 MP, F2.8-22, <0.3% distortion. That image circle covers the 1/1.7-inch sensor with margin. The focal-length algebra behind step 3 is the same as any ground job; how to choose a machine vision lens focal length walks it.

Wide-plus-detail beats zoom on a vibrating platform, because varifocal and zoom settings walk under vibration and temperature. The LS-FFL-1582 prints 8 mm and a 57.6° field for a 2/3-inch sensor — the coverage partner while a longer lens holds the detail. Lock the focus mechanically once set.

Two fixed lenses from the same series show the split between coverage and detail:

All 2 share: Mount C-mount; Flange back 17.526 mm in air. Values as printed in each product's data sheet; open a part for its drawing and full specifications.

Sealing and temperature

Rain, dust and condensation are housing problems, not sensor problems. A machine-vision camera is a vented component; the payload does the environmental work: a sealed housing with a flat optical window parallel to the sensor, glanded connectors and desiccant against the fog that follows a cold soak at altitude. Match the housing rating to the weather you fly — the NEMA 4X versus IP66 ratings page explains why the immersion and jet-test numbers are not interchangeable.

Focus walks with temperature across a flight day, and a sun-to-shade cycle at altitude is harsher than any factory shift. Set focus at the working altitude, lock it, and re-verify after the first hot-and-cold cycle; the diagnosis method is in camera focus drift with temperature.

Where drone builds usually go wrong

• Megapixels first. A high-resolution sensor behind an underrated lens and a rolling shutter returns blur, not detail, and tiny pixels ask more of the optics and the light — the trade is quantified in small pixel camera selection.
• Zoom and varifocal optics. Settings walk under vibration. Fixed focal lengths, locked.
• One camera for everything. Piloting off the compressed mapping stream adds the latency budget; keep the pilot feed raw and separate.
• Calibration skipped. Photogrammetry needs per-unit intrinsic calibration to align images with GPS and LiDAR; geometric camera calibration for UAV visual navigation covers the alignment.

Checks before the first flight

• GSD at the planned altitude, from the formula, at or below half the smallest feature.
• Lens image circle ≥ sensor diagonal; lens megapixel rating ≥ sensor rating; distortion under 0.3% for photogrammetry.
• Exposure ≤ GSD ÷ ground speed, checked against the worst light of the day.
• Global shutter for any line flight; rolling only for short-exposure hover work.
• Pilot chain measured glass-to-glass under 50 ms.
• Mass budget: camera, lens, housing, cable and compute against the platform, at about 2-4 W per camera.
• Housing sealed, window clear of the footprint corners, desiccant fitted.
• Focus set at working altitude and locked.
• Trigger wiring into the flight controller kept clean and isolated — camera GPIO wiring shows how to prevent damage and triage power faults.
• Storage sized for the overlap plan: about 62 GB per flight hour at 1.4 frames per second, 8-bit mono.

One line per case, then. Inspection of 5 mm defects from 50 m: a 4000 × 3000, 1/1.7-inch sensor with a 50 mm lens, global shutter, 0.9 ms exposure, about 62 GB of storage per hour, in a sealed housing. Coverage mapping with a detail channel: the 8 mm wide lens low and slow for the passes, the 16 mm 20 MP lens for the measurement frames. Build the shortlist in the camera configurator, filter the lens finder by focal length, or send us the altitude, target size and platform limit through a quote or the contact page. More selection guides sit on the cameras topic page.