How does it work a 3D Laser Scanner
For some years now, in the market of surveying and metrology, have made their appearance the 3D laser scanner that are increasingly being used for the acquisition of geometric information in various sectors and for different fields of application.
This technology has greatly speeded up the phase of acquisition of 3D coordinates that define the geometry of a detected object, be it a building or a plant, performed by scanning the space and acquiring point clouds at a speed that arrives now up to a million points per second.
But really how does it work a 3D laser scanner?
The basic principle is the emission of a light signal (Laser) by a transmitter and receiving the return signal by a receiver. In the receiving phase the scanner uses different techniques for distance calculation that distinguish the type of instrument.
Depending on the technique used, the 3D laser scanner are defined ‘time of flight’ (TOF) when calculating the distance according to the time elapsed between the emission of the laser and the reception of the return signal, or ‘phase shift based’ when the calculation is performed by comparing the phases of the output signal and the return.
The most scanners on the market today are of two types described, although there are also so-called ‘trangulation scanners’. An example of time of flight scanner is the Leica P40, while the phase based scanner are the Z+F 5010X and the Faro Focus X330.
The emitter is mounted on a body that rotates around a vertical axis which contains a mirror rotating on its horizontal axis, which has the function of reflecting the laser and direct it toward the point detected. The movement of the body and mirror occur at very high speeds, allowing the acquisition of data at a speed of up to one million points per second.
Setting the acquisition paramethers
The speed and the pitch of the rotations can be set by the operator, acting on these parameters determines the resolution of the scan, that is the density of the grid of points detected at a certain distance, and the quality of the acquired data, typically higher when the scanner rotates slowly. The two parameters therefore also determine the duration of the scan that can vary from about thirty seconds up to several tens of minutes to complete 360° scans.
During the acquisition the scanner stores, for each measured point, the computed distance and also horizontal and vertical angles based on the position of the body and of the mirror. In addition to this information, it also acquired the value of reflectance of the surface affected by the laser that will be much higher when the surface will tend to be white.
All modern 3D laser scanner mount also an integrated digital camera that, after the acquisition of the geometric data, is used by automatic procedures for the acquisition of images of the space detected. The photos will then stich together by software provided by the manufacturers (Cyclone for Leica, Laser Control for Z + F and Scene for Faro) and applied to point clouds to enrich the color information.
The end result will be a colored cloud of 3D points (3D Point Cloud), representing three-dimensional space around the point of scanning, characterized by a high accuracy, which can be used to extract 2D and/or 3D deliverables.