Laser and other light-based systems may be affected by the color of a surface or if it is transparent or reflective. As more experience has been gained over the years, however, users have become adept at work-arounds for surface problems which may cause errors. One must also be appropriately safety conscious when using any laser source. Even though most lasers used for scanning are rated well below any harmful threshold, reflections on curved surfaces and other inadvertent events can result in a potentially harmful focused beam.

Dual-Capability Systems
Many companies that make contact digitizing instruments, as well as many of those that make laser scanners, provide turnkey products that have both of these quite complementary capabilities. Broad areas can be quickly scanned using a laser device mounted on the arm, and features which might be geometrically problematic for the laser can be contact-probed. Some companies provide instruments which can carry both a contact probe and a laser head simultaneously.

A few companies provide color laser scanning technology. Arius 3D uses a multiplexed arrangement of red, green and blue lasers to simultaneously gather color and geometric data. The company mainly offers scanning services, however, rather than selling equipment. Other companies such as Minolta and Cyberware use laser scanning to gather surface measurements and combine that data with color video information gathered separately. Most color scanners use structured white light or broadband sources. See that section.

Other Types of Laser Systems
Several additional laser technologies are also utilized, including time of flight, optical radar and laser tracking. In general, these methods offer good accuracy combined with the capability of making measurements from a long distance away from the subject - in some cases tens of meters. This so-called "stand-off" distance is important for applications such as digitizing large machinery, buildings, and the like, which represent a large fraction of the applications for these technologies.

Time of flight systems measure how long it takes for light emitted by a laser to return to a sensor located near its source. Optical radar systems are similar in operation, and both are analogous to standard radar systems which measure the return-time of a radio wave. Time of flight and radar systems don't usually require retroreflectors mounted on the object to be measured and can operate at very high rates to quickly capture entire scenes or objects. In contrast, laser trackers look for a signal in their field of view from a retroreflector placed or held on the object. The main advantage these systems offer is high precision over a large working volume and a frequent use is for aligning large pieces of machinery or verifying as-built dimensions of large objects.

Other Types of Tracking Systems           Directory of Commercial Providers of this Technology ...
In addition to laser-based tracking systems, a number of companies make LED-based and other types of tracking systems, such as magnetic trackers. These technologies generally have smaller working envelopes than laser-based systems and may not be quite as accurate. They're most frequently used in human and other types of motion studies, but are also useful for reverse engineering. A probe with one or more LED's is touched or attached to the object to be digitized. Sensors, most often utilizing CCD chips in a dual camera arrangement, image the LED's in their field of view. As with laser scanners, trigonometry is then used to calculate the position of the probe on the surface of the object. Encoding schemes based on high-speed modulation of the light emitted by the LED's allow some instruments to simultaneously track the position of hundreds of LED's.

Magnetic trackers offer the added benefit of being able to digitize points on objects that are not within a direct line of sight. Instead of an LED probe, these systems use a small wire coil as a target. One company that makes magnetic trackers, Polhemus, combines this technology with laser scanning. The result is a system that has many of the same features as laser scanners mounted on mechanical arms, while providing very great freedom of movement.

In RE applications, these systems provide good accuracy over a substantial volume and moderate speeds. They aren't affected by surface quality or color. On the down-side, they require a contacting probe or marker and can be slow to digitize complex surfaces.

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Scanning Technologies at a Glance      Mechanical Touch-probe Systems      Laser-based Systems      Structured-light or Broadband-source Systems      Seeing Inside - Internal Viewing Technologies RE Technology Comparison Chart	3D Metrology Systems for Manufacturing Scanners for Very Large Objects and Surveying Applications Commercial Manufacturers Directory