3D laser scanning is performed with special devices, scanners, which detect spatial positions of points on surveyed surfaces. It represents a non- contact method of surveying via active (emitted) light. Each point is measured by a laser light beam of specific wavelength and diameter. There are two methods of range measurement: with the laser pulse and with phase modulation. In each method the laser beam is emitted to an object from which it is reflected back to the scanner. Pulse scanners calculate the distance of the point by measuring the time needed for the pulse to reflect back to the scanner. In phase scanners, the emitted beam has a specific frequency modulation, and a phase shift is measured in the reflected beam to determine the distance to the point.
When dealing with objects that are complex in geometry, scanning from one position will not provide enough information about all its surfaces. In cases such as this, scanning is performed from multiple positions. These scans are later on merged to one 3D model.
The intensity of the reflected beam is also measured. This data gives us information about the type of surface we are surveying.
Newer models of scanners have integrated cameras. These cameras take color pictures which are later on used for colorising cloud points and models.
Ranging error for these devices is usually around 3mm.
Recorded 3D data is processed in specialized computer software.