Terrestrial laser scanning (TLS) captures detailed 3D information of an environment by emitting laser pulses and measuring the time it takes for them to return.
At its core, TLS uses a lidar (Light Detection and Ranging) device on a tripod to scan an area around it. Here's a breakdown of the process:
The Basics of TLS
- Deployment: A TLS device, which is essentially a sophisticated lidar scanner, is set up on a stable tripod at a specific location within the area of interest.
- Scanning: The scanner rotates and tilts, systematically covering the surrounding environment.
- Pulse Emission: The device sends out rapid pulses of laser light.
- Surface Interaction: These light pulses travel outward and bounce off a surface they encounter, such as walls, objects, ground, or vegetation.
- Signal Return: The reflected light pulses travel back towards the transmitter within the scanner.
- Time Measurement: The scanner precisely measures the time it takes for each pulse to travel from the device to the surface and back.
- Distance Calculation: Since the speed of light is known, the scanner can calculate the distance to the surface based on this travel time.
- Angle Recording: Along with distance, the scanner also records the precise angle (horizontal and vertical) at which the pulse was sent and received.
- Point Cloud Creation: By combining the distance and angle information for millions or billions of pulses, the scanner creates a dense collection of 3D points, known as a "point cloud." Each point represents a location in space where a laser pulse hit a surface.
Key Components
| Component | Function |
|---|---|
| Lidar Scanner | Emits pulses and receives returning signals |
| Tripod | Provides a stable platform for scanning |
| Rotation/Tilt | Allows the scanner to cover a full area |
| Software | Processes data, creates point clouds, registers scans |
What Does TLS Produce?
The primary output of a TLS scan is a highly accurate 3D point cloud. This point cloud serves as a digital representation of the scanned environment.
- Visualisation: Point clouds can be viewed and navigated in 3D software.
- Measurement: Accurate distances, areas, and volumes can be extracted directly from the point cloud.
- Modeling: The point cloud can be used as a basis for creating detailed 3D models (e.g., Building Information Models - BIM, meshes).
- Analysis: Changes over time, structural deformation, or volumetric calculations can be performed using point cloud data.
Applications of TLS
TLS is used across various industries due to its speed and accuracy in capturing complex 3D data.
- Architecture & Construction: Documenting existing buildings, monitoring construction progress, verifying as-built conditions.
- Engineering: Structural analysis, deformation monitoring, topographic surveying.
- Cultural Heritage: Preserving digital records of historical sites and artifacts.
- Forensics: Documenting crime scenes or accident sites.
- Manufacturing: Quality control, dimensional inspection of large components.
In essence, TLS leverages the principles of lidar to remotely capture detailed 3D spatial data by measuring the time-of-flight of laser pulses, creating a precise digital copy of the scanned reality.
