A 3D scanner is a device that analyzes a real-world object or environment to collect data on its shape and possibly its appearance (i.e. colour). The collected data can then be used to construct digital, three dimensional models.
Industries and users who traditionally work with two-dimensional plans and schematic diagrams are increasingly discovering the advantages of three-dimensional planning and documentation tools through the use of 3D laser scanners. Traditionally, measurements are collected using a combination of tools such as measuring tapes, total stations, digital cameras, and laser range finders; however, the use of 3D laser scanners allows companies to gather measurement data with a single solution while significantly reducing data collection errors and streamlining the overall workflow.
Capturing high resolution three-dimensional images of complex environments and geometries, large-volume 3D laser scanners provide a fast, efficient way to capture millions of data points for use in comprehensive 3D models or detailed reconstructions. Used in applications ranging from forensic and crime scene investigation to surveying, facility management and historic preservation, 3D laser scanners are a versatile, accurate solution that allows companies to obtain data they previously couldn’t, helping them to make more informed decisions while saving valuable time and money.
Many different technologies can be used to build these 3D scanning devices; each technology comes with its own limitations, advantages and costs. Many limitations in the kind of objects that can be digitized are still present, for example, optical technologies encounter many difficulties with shiny, mirroring or transparent objects.
There are many different approaches to 3D scanning, based on different principles of imaging. Some technologies are ideal for short-range scanning, while others are better for mid- or long-range scanning.
Laser triangulation scanners use either a laser line or single laser point to scan across an object. A sensor picks up the laser light that is reflected off the object, and using trigonometric triangulation, the system calculates the distance from the object to the scanner.
The distance between the laser source and the sensor is known very precisely, as well as the angle between the laser and the sensor. As the laser light reflects off the scanned object, the system can discern what angle it is returning to the sensor at, and therefore the distance from the laser source to the object’s surface.
Structured light scanners also use trigonometric triangulation, but instead of looking at laser light, these systems project a series of linear patterns onto an object. Then, by examining the edges of each line in the pattern, they calculate the distance from the scanner to the object’s surface. Essentially, instead of the camera seeing a laser line, it sees the edge of the projected pattern, and calculates the distance similarly.
Laser pulse-based scanners, also known as time-of-flight scanners, are based on a very simple concept: the speed of light is known very precisely, so if we know how long a laser takes to reach an object and reflect back to a sensor, we know how far away that object is. These systems use circuitry that is accurate to picoseconds to measure the time it takes for millions of pulses of the laser to return to the sensor, and calculates a distance. By rotating the laser and sensor (usually via a mirror), the scanner can scan up to a full 360 degrees around itself.
Laser phase-shift systems are another type of time-of-flight 3D scanner technology, and conceptually work similarly to pulse-based systems. In addition to pulsing the laser, these systems also modulate the power of the laser beam, and the scanner compares the phase of the laser being sent out and then returned to the sensor. For reasons that are beyond this web page’s scope, phase shift measurement is more precise.
How the Faro Focus 3D Works
Large-Volume 3D Laser scanners like the Faro Focus 3D use infrared laser technology to produce exceedingly detailed three-dimensional images of complex environments and geometries in only a few minutes. The resulting images are an assembly of millions of 3D measurement points, known as a point cloud.
The laser scanner works by emitting a beam of infrared laser light and reading the energy reflected back to the scanner to place a point in 3D space.
The laser is sent from the scanner onto a rotating mirror that projects a flat plane of laser light out from the scanner. The entire head of the scanner then rotates, sweeping the laser across the desired area. Objects in the path of the laser will reflect energy back to the scanner and the scanner will place a point in 3D space.
The density of the points collected is controlled by the rotation speed of the scanner. The slower the scanner turns, the denser the pattern of points collected, while the faster the scanner turns, the resulting point cloud is less dense. In this manner, millions of discrete measurements can be collected in a matter of minutes.
For most situations, a single scan will not produce a complete model of the subject. Multiple scans, even hundreds, from many different directions are usually required to obtain information about all sides of the subject. These scans have to be brought into a common reference system, a process that is usually called alignment or registration, and then merged to create a complete model. The use of reference targets or objects in the scan environment can be used to tie together multiple scans, each on their own coordinate system onto a single, aligned coordinate system. This allows extremely complex environments to be documented quickly and accurately. This whole process, going from the single range map to the whole model, is usually known as the 3D scanning pipeline.
Collected 3D data is useful for a wide variety of applications. These devices are used extensively by the entertainment industry in the production of movies and video games. Other common applications of this technology include industrial design, orthotics and prosthetics, reverse engineering and prototyping, quality control/inspection and documentation of cultural artifacts.
The purpose of a 3D scanner is usually to create a point cloud of geometric samples on the surface of the subject. These points can then be used to extrapolate the shape of the subject (a process called reconstruction). If colour information is collected at each point, then the colours on the surface of the subject can also be determined.
3D scanners share several traits with cameras. Like cameras, they have a cone-like field of view, and like cameras, they can only collect information about surfaces that are not obscured. While a camera collects color information about surfaces within its field of view, a 3D scanner collects distance information about surfaces within its field of view. The "picture" produced by a 3D scanner describes the distance to a surface at each point in the picture. This allows the three dimensional position of each point in the picture to be identified.