What is lidar? How lidar scanners work and where they are used

What is lidar and what does lidar mean?

If you are asking what is lidar, the short answer is that it is a way of measuring the world with laser light. The word stands for light detection and ranging: a lidar sensor emits laser energy, detects the light reflected from a surface and converts the timing or phase of that return into a distance.

On its own, one distance is not very useful. A lidar scanner becomes powerful because it also records the exact horizontal and vertical angle of every measurement. Distance plus two angles gives an X, Y, Z coordinate, and a scanner repeats this hundreds of thousands to millions of times per second.

The result is a point cloud: a dense set of 3D points, often with intensity and colour values, that describes the shape of buildings, terrain, plant rooms, roads or industrial parts. Engineers then measure, model and compare that data instead of revisiting the site.

How does lidar technology work?

Lidar technology works by measuring how long light takes to reach a target and come back, or by measuring the phase change of a modulated beam. Both methods rely on the constant speed of light, roughly 300,000 km per second.

Time-of-flight (pulsed) lidar

A pulsed scanner sends a short laser pulse and times its return. Distance equals the speed of light multiplied by the round-trip time, divided by two. Because pulses can be strong and short, time-of-flight units reach long ranges and work well outdoors and from aircraft.

Phase-shift lidar

A phase-shift scanner emits a continuous beam modulated at known frequencies and compares the phase of the outgoing and returning signal. This allows very high measurement rates and low noise at short to medium range, which is why many terrestrial scanners for buildings use it.

Deflection and positioning

Mirrors, rotating heads or solid-state optics steer the beam across the scene. Terrestrial scanners rotate on a fixed tripod, while mobile and airborne lidar systems add GNSS and an inertial measurement unit (IMU), or SLAM software, to know where the sensor was at each instant.

What are the main types of lidar systems?

Lidar systems are usually grouped by how the sensor is carried: from the air, on a tripod, on a vehicle or in the hand. The platform decides coverage speed, accuracy and cost more than any single sensor spec.

Figures are typical ranges, not guarantees. Real accuracy depends on range, target surface, calibration, georeferencing and processing. For a deeper look at tripod-based work, see our guide to terrestrial laser scanning accuracy and field workflow.

2D lidar versus 3D lidar

A 2D lidar sensor scans a single plane, which suits obstacle detection on robots and safety systems. A 3D lidar scanner adds a second axis of rotation or multiple beams, so it captures full volumes. Surveying and lidar mapping almost always require 3D data.

What does a lidar scanner do in surveying and construction?

In surveying and construction, a lidar scanner captures existing conditions completely and quickly, so teams measure in the office rather than in the field. It replaces many individual tape, total station or GNSS shots with millions of points.

• Lidar topography and topographic surveys: airborne and drone lidar produce bare-earth terrain models, contours and slope analysis over large areas.
• As-built and scan-to-BIM: terrestrial scanners record structural, mechanical and architectural detail for renovation and clash checks.
• Infrastructure mapping: mobile lidar surveys of roads, bridges, tunnels and rail capture clearances and surface condition.
• Volumes: stockpiles and earthworks can be measured from repeat scans.
• Deformation monitoring: comparing scans over time reveals settlement or movement.

A lidar scanner for construction is most useful when the site is complex, congested or hazardous, because the crew stands back and captures everything in one pass. Our overview of SLAM scanning and handheld mobile mapping covers walk-through capture for interiors and tunnels.

How accurate is lidar, and what limits lidar range?

Lidar accuracy depends mainly on the platform, the distance to the target and how well the data is georeferenced. Terrestrial scanners are typically the most accurate; airborne systems trade accuracy for coverage.

Lidar range is limited by laser power, eye-safety class, the reflectivity of the surface and the measurement rate. Dark, wet or shiny surfaces return less light, so specifications normally quote range against a stated reflectivity, such as 90 % white or 18 % grey. Faster measurement rates usually mean shorter maximum range.

As a real example, our terrestrial 3D laser scanner measures up to 2 million points per second with a 0.5–70 m or 0.5–150 m range (white, 90 %). Its long-range version reaches 614 m at 0.5 Mpts/s but 153 m at 2 Mpts/s, which shows the speed-versus-range trade-off clearly.

Lidar wavelength and eye safety

Most survey lidar uses near-infrared light. Wavelengths around 905 nm and 1550 nm are common; the 1550 nm band allows more power within eye-safety limits. Green light near 532 nm penetrates water and is used for lidar bathymetry. Laser safety classes are defined in IEC 60825-1, and Class 1 means eye-safe under normal use.

Lidar vs laser scanning vs photogrammetry

Lidar and laser scanning are essentially the same technology; "laser scanner" is the common term for tripod and handheld survey instruments, while "lidar" is used more for airborne, automotive and mobile sensors. The debate of laser vs lidar is mostly vocabulary.

The more useful comparison is lidar against photogrammetry, which builds 3D models from overlapping photos.

Many projects combine both: lidar for geometry and a camera for colour. A "lidar camera" usually means exactly that pairing of a depth sensor with an RGB camera.

Lidar data processing: from raw scans to deliverables

Raw lidar data becomes useful only after processing: registration, cleaning, classification and modelling. Budget office time for this, because it often takes longer than the fieldwork.

1. Import and register: align individual scans into one coordinate system using targets, overlapping geometry or GNSS/IMU trajectories.
2. Georeference: tie the cloud to survey control so it fits project coordinates.
3. Clean: remove noise, moving objects and stray points.
4. Classify: separate ground, vegetation, buildings and other classes, especially for terrain models.
5. Extract deliverables: digital terrain models, contours, sections, 2D drawings, meshes, lidar 3D modeling or BIM elements.
6. Export: open formats such as LAS/LAZ and E57 keep data portable between applications.

Our guide to point cloud processing and registration explains each step in more detail.

Lidar cost and how to choose a lidar scanner

Lidar cost varies more by platform and accuracy class than by brand. Low-cost lidar sensors for robotics are inexpensive, while survey-grade terrestrial, handheld and airborne lidar systems are professional capital equipment.

As a broad, typical guide, survey-grade handheld and terrestrial scanners are usually priced in the tens of thousands of US dollars, and airborne lidar systems higher. Software, training and processing time add to the total. Use these only as orientation; exact lidar price depends on configuration.

When choosing, answer these questions first:

• What deliverable do you need, and at what accuracy?
• Is the work mainly indoors, outdoors, or on long corridors?
• What maximum range and scan speed does a typical site need?
• Do you need georeferencing to GNSS control?

For a walk-through workflow, the handheld SLAM laser scanner weighs 925 g and delivers point-cloud thickness of ≤ 1 cm after post-processing. Mars Geosystems supplies scanners from one unit, with OEM options for distributors; you can request a quote for lidar equipment with your project details.

Frequently asked questions