Terrestrial laser scanning (TLS): how it works, accuracy and field workflow

What is terrestrial laser scanning?

Terrestrial laser scanning (TLS) is a ground-based survey method in which a 3D laser scanner, mounted on a tripod, records the geometry of its surroundings as a point cloud. The scanner stays still during each scan, then the operator moves it to the next station until the whole site is covered.

Because each setup is static and close to the subject, TLS produces dense, low-noise data with millimetre-level detail at short range. That makes it the standard method for as-built documentation of buildings, industrial plants, tunnels, bridges and heritage structures.

TLS is one branch of laser scanning. Airborne laser scanning works from aircraft and drones, and mobile laser scanning works from vehicles, backpacks or handheld devices. If you are choosing between instrument types, our 3D laser scanner buying guide compares them side by side.

How does terrestrial laser scanning work?

A terrestrial laser scanner measures a distance and two angles for every point, then converts them into XYZ coordinates relative to the scanner.

The laser rangefinder works in one of two ways. A time-of-flight scanner times short pulses to the target and back; a phase-shift scanner compares the phase of a modulated continuous beam. Time-of-flight suits long ranges, while phase-shift scanners are typically faster and less noisy at short to medium ranges.

To cover the scene, a fast-spinning mirror deflects the beam vertically while the scanner head turns slowly through 360° horizontally. The result is a near-spherical field of view; only a cone below the instrument is hidden by the tripod. Each point also stores the strength of the returned signal (intensity), and most scanners take panoramic photos to colourise the cloud.

The angular step chosen by the operator sets point spacing. At 10 m, for example, a finer step gives closer points but increases scan time and file size, so resolution is always a trade-off against productivity.

Terrestrial vs airborne vs mobile laser scanning

The three main laser scanning platforms differ in coverage speed, viewpoint and achievable accuracy. The comparison below shows typical characteristics.

Projects often combine methods: airborne laser scanning for terrain, TLS for structures that need detail, and handheld SLAM mobile mapping to fill in interiors quickly.

What controls laser scanner accuracy?

Laser scanner accuracy on a real project is a chain of error sources, and the weakest link usually decides the result.

• Range noise: random scatter in distance, which increases on dark, wet or distant surfaces.
• Angular accuracy: small angle errors grow with distance, so far points are less precise.
• Angle of incidence: a beam hitting a surface at a grazing angle produces a stretched footprint and noisier points.
• Surface properties: glass, polished metal and water can reflect the beam away or create false points.
• Beam divergence and mixed pixels: at edges the footprint can straddle two surfaces, creating phantom points that need filtering.
• Registration and georeferencing: the residuals of joining scans and fitting them to control.
• Calibration and environment: instrument calibration, temperature and vibration.

Field test procedures for terrestrial laser scanners are described in ISO 17123-9. Running a simple check on known distances before an important job is good practice for any 3D laser scanning survey.

Targets, registration and georeferencing

Registration joins individual scans into one point cloud; georeferencing places that cloud in a project or national coordinate system.

There are three common registration approaches. Target-based registration uses spheres or checkerboard targets visible from several stations. Cloud-to-cloud registration matches overlapping geometry directly and needs good overlap and distinct shapes. Traverse-style registration sets the scanner over known points and orients it to a backsight, much like a total station.

For georeferencing, 3D laser scanning targets are coordinated with a total station or GNSS rover. A scanning total station can do both jobs from one instrument. Always keep a few targets out of the adjustment as independent checks, and record the registration report with the project. Our guide to point cloud registration and processing covers the office side.

Terrestrial laser scanning field workflow

A disciplined workflow is the most effective way to get accurate, complete scans on the first visit. A typical TLS job follows these steps:

1. Define the deliverable: agree the required accuracy, level of detail and coordinate system with the client before planning stations.
2. Plan stations: use drawings or a walk-through to place stations with clear lines of sight, typical overlap of 30 % or more between neighbours, and short ranges to critical areas.
3. Set control and targets: establish control points and place targets where several stations can see them.
4. Choose scan settings: pick resolution and quality based on the closest and farthest surfaces that matter, and decide whether colour imagery is needed.
5. Scan and photograph: level the scanner, scan, then capture imagery. Avoid people walking through critical areas.
6. Check in the field: do a preliminary registration on site to spot gaps before leaving.
7. Back up data: copy raw scans and field notes to two separate storage devices daily.

3D laser scanning applications in construction and industry

TLS is most useful where geometry is complex and errors are expensive. Typical applications include:

• 3D laser scanning in construction: as-built records, floor flatness, steel and formwork checks, and comparing what was built against the design model.
• Buildings and architecture: measured surveys of existing buildings for renovation, producing plans, sections and elevations.
• Industrial plants: capturing pipework and equipment for retrofit and clash detection, reducing site visits during shutdowns.
• Topographic surveys: dense terrain capture for quarries, embankments and complex sites where manual spot heights would miss detail.
• Tunnels, bridges and heritage: deformation monitoring, clearance checks and conservation records.

The benefits of laser scanning in construction come mainly from fewer return visits, earlier detection of clashes and a permanent record that can be measured later.

Terrestrial laser scanning equipment and cost

A complete TLS kit includes the scanner, tripod, targets, batteries, a field tablet, processing software and a workstation. Survey-grade terrestrial scanners typically cost tens of thousands of US dollars, with long-range models at the upper end; prices vary by region and configuration.

Mars Geosystems offers two terrestrial scanners on our 3D laser scanners page. The phase-shift scanner measures up to 2 Mpts/s over 0.5–150 m (on 90 % white targets), with up to 266 MPx colour and a 4.4 kg weight. Its long-range version reaches 614 m at 0.5 Mpts/s. The high-speed scanner provides up to 1000 kHz, 0.6–150 m range, a 360° × 282° field of view and a Class 1 eye-safe laser under IEC 60825-1.

For a configuration matched to your projects and typical ranges, send details through the quote request form.

Frequently asked questions