August 26, 2013

3D Laser Scanning: Is the process of collecting 3D coordinates of an object’s surface with laser measurements in an automated manner and at a high rate (up to hundreds of thousands of points per second). Line-of-sight to the object surface is required and the result is similar to a photograph with depth information.

In terrestrial laser scanning this process is realized by an instrument – laser scanner system – generally comprised of four main components: laser unit, deflecting/rotating unit, ranging unit, and control and data recording unit. The laser unit emits the laser beam/pulses in one direction and the deflecting/rotating unit will direct the laser signal to multiple directions using a rotating polygon mirror and by rotating the entire laser scanner body. The ranging unit detects the returned signal and processes the information to determine distances and angles and finally 3D coordinates (e.g. North, East, Elevation). The control and data recording unit has a role in the laser scanner operation and data storing. This component can be separate from the scanner body, in a data collector or notebook computer, or integrated into the scanner system.

Courtesy of Trimble Navigation Limited

The technical specifications of commercially available laser scanner systems include: scan method (time-of-flight, phase difference), field of view (horizontal, vertical), scan range distance (maximum, operating, and minimum), scan speed, angle resolution (horizontal, vertical), scan range accuracy, digital camera specifications, and inclination sensor.

A single session of data collection at a particular location (one origin and one orientation) is referred to as a scan. The resulting collection of points with 3D coordinates in a 3D coordinate system is called a point cloud. Additional information at each point may also include colour from the digital camera and reflectivity. In most cases multiple scans are necessary in order to capture the entire object surface.  Subsequently a process of transforming each point cloud onto a common coordinate system takes place. This process is referred to as registration or alignment. The resulting data set can now be viewed, manipulated, analyzed and modeled to produce and extract digital information, two-dimensional drawings, and three dimensional models. Usually for the purpose of presentation, a 2D or 3D representation of the data model is created by the process of rendering by means of a computer program.  These deliverables are relevant for a wide range of applications in sectors such as oil and gas, mining, cities and municipalities, industrial units (plants, factories, and shops), civil engineering, architecture, construction, heritage preservation, etc.

The process of laser scanning comprises the following steps: survey planning, field data acquisition, data preparation, data registration, data quality control and analysis, data modelling and extraction of information, and delivery of product.

The resulting benefits of using 3D laser scanning include safety and risk mitigation (e.g. hazardous areas can be surveyed without requiring personnel to physically access the area; less personnel are required), speed, accuracy, portability and flexibility, and cost effectiveness.