How does LiDAR work?

LiDAR — Light Detection and Ranging — is a survey technique that uses laser pulses to measure the geometry of physical spaces, structures, and surfaces. It has become the standard tool for as-built capture, façade survey, and BIM-ready geometry capture in UK construction.

The basic mechanism

A LiDAR scanner contains a laser emitter, a receiver, and a precise positioning system. To measure each point:

1. The laser emits a short pulse of light in a known direction.
2. The pulse travels to the nearest surface in that direction and reflects.
3. The receiver detects the returning pulse.
4. The system measures the round-trip time.
5. Distance = (speed of light × time) / 2.
6. Combined with the known direction, distance becomes a 3D coordinate.

A modern terrestrial LiDAR scanner emits roughly a million pulses per second, sweeping through a full sphere from each setup position. Each pulse becomes a point in the resulting cloud.

Scanner types

Different LiDAR platforms suit different applications:

• Terrestrial (tripod-mounted). The accuracy backbone — millimetre-grade engineering capture.
• Mobile (handheld, backpack, vehicle-mounted). Faster and more reachable; typically centimetre-grade accuracy with SLAM-based registration.
• Drone-mounted. Aerial reach with engineering-grade distance measurement.
• Static long-range. For very large structures and outdoor scenes.

What it captures

Each LiDAR point carries:

• 3D position (X, Y, Z).
• Intensity (how strongly the surface reflected the pulse).
• Often colour (from an integrated camera).

Together, millions of points make up a measurable, photorealistic record of every surface within line of sight to the scanner.

Registration

Most LiDAR surveys involve multiple scan stations. Registration ties them into a single coherent dataset:

• Common targets (typically reflective spheres or chequerboards) are placed in overlapping zones.
• Each station captures the targets along with the surrounding geometry.
• Software calculates the transformation that aligns each station with the others.
• The result is a registered point cloud accurate to a few millimetres across the whole capture.

Registration accuracy is reported as part of the deliverable.

Where it wins

• Indoor and shaded environments where photogrammetry struggles.
• Plain or reflective surfaces that confound photogrammetric processing.
• Highest-accuracy engineering capture.
• Structural monitoring with repeat captures.
• Complex geometry with deep recesses.

Where photogrammetry wins

For large external sites with good light and well-textured surfaces, drone photogrammetry is often more cost-effective. The two methods are complementary; the right surveyor picks by application.

Deliverable formats

Common formats:

• E57 — open, vendor-neutral.
• RCP / RCS — Autodesk’s format, for Revit and other Autodesk tools.
• PLY, PTS, LAS — specialist downstream uses.

For more detail, see What is LiDAR scanning in construction and What is a point cloud survey.