LiDAR vs photogrammetry — which survey method is right for you

LiDAR and photogrammetry both produce 3D point clouds — the underlying deliverable looks similar enough that they are sometimes assumed to be interchangeable. They are not. Each has clear strengths and clear weaknesses, and choosing the wrong one for your project can produce data that is unfit for purpose. Here is the honest comparison.

How they work

LiDAR uses laser pulses. The instrument sends a pulse, measures the time of flight to the surface and back, and calculates distance. Combined with the known direction of the pulse, the result is a 3D coordinate per pulse. Modern terrestrial scanners produce around a million points per second.

Photogrammetry uses overlapping photographs. Software identifies common features across many images, solves the camera positions, and triangulates 3D coordinates for every common feature. The result is a dense 3D point cloud derived from the images.

The two technologies use fundamentally different physics. The choice between them is usually driven by site condition, accuracy requirement, and deliverable.

Where LiDAR wins

Indoor and shaded environments. LiDAR does not need light. A dim corridor, a windowless plant room, the underside of a bridge, the inside of a tank — all are easy for LiDAR and impossible for photogrammetry.

Plain or reflective surfaces. Photogrammetry needs surface texture to match features across images. A plain white wall, glass, water, polished steel — all confound photogrammetric processing. LiDAR returns a useful pulse from any of them (subject to the angle of incidence).

Highest accuracy. A registered LiDAR survey produces a few-millimetre point cloud across the entire capture. Photogrammetry can match that accuracy in ideal conditions, but more often produces accuracy in the centimetre range.

Engineering structures. Bridges, viaducts, retaining walls, tunnels — LiDAR captures the geometry better than any photogrammetric flight, particularly where the structure is complex or where access is constrained.

Repeatability for monitoring. When you need to come back in six months and detect movement at engineering tolerance, LiDAR with the same control network is the right choice. Photogrammetry can be made to work but is more sensitive to environmental conditions between captures.

Where photogrammetry wins

Large external sites. A drone-mounted photogrammetric flight covers a large site quickly and cheaply. LiDAR equivalents (drone-mounted LiDAR or terrestrial scanning every few metres) take much longer and cost more.

Visual record. The output of a photogrammetric capture is photographic — every surface is rendered with its true colour and texture. For documentation, dispute resolution, and visual communication, photogrammetry produces a more readable deliverable.

Orthomosaics. A drone photogrammetric flight produces a high-resolution geo-referenced orthomosaic of the site. There is no equivalent direct deliverable from LiDAR alone.

Aerial inspection. For roof, façade, or chimney inspection, a drone-mounted photogrammetric capture produces inspection-ready imagery alongside the 3D model. LiDAR is structurally accurate but does not produce the inspection imagery in the same pass.

Cost on the right job. For external, well-lit, well-textured sites, photogrammetry is cheaper than LiDAR for an equivalent deliverable.

Where they converge

Some payloads now combine LiDAR and photogrammetric capture in the same flight or scan. The deliverable is a registered LiDAR cloud with photogrammetric texture overlaid, or a photogrammetric model with LiDAR-derived high-accuracy control points. For complex jobs, this combined approach offers the best of both methods at a small cost premium.

Choosing between them

A short decision tree:

• Is the capture indoors or in a shaded environment? LiDAR.
• Are the surfaces plain, glassy, or reflective? LiDAR.
• Is the site large, external, well-lit, well-textured? Photogrammetry (probably from a drone).
• Is the brief about visual documentation and orthoimagery as much as geometry? Photogrammetry.
• Is the brief structural monitoring with millimetre tolerances? LiDAR with controlled targets.
• Is the structure complex with deep recesses or constrained access? LiDAR.
• Is the brief mixed? Use both.

Common scoping mistakes

Specifying photogrammetry for an interior. Particularly for plain or reflective interiors. The output will have gaps and noise where it matters most. Use LiDAR.

Specifying LiDAR for a large external area progress capture. The cost will be higher than a drone photogrammetric flight that produces equivalent quality for the brief.

Confusing accuracy with point density. A photogrammetric model can have many more points than a LiDAR scan and still be less accurate. Density and accuracy are not the same metric.

Assuming the surveyor will pick the method. They might, but the brief should be explicit. Specify the deliverable, the accuracy required, and the conditions; let the surveyor justify the method against the specification.

Practical advice

Both methods are mature, both produce defensible deliverables when used appropriately, and both have a place in a modern survey toolkit. The right surveyor will be able to talk through the trade-offs for your specific brief in a few minutes. If they cannot — or if they push their preferred method without engaging with the question — get a second opinion before committing.