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Article:3D scanner
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== Technology ==
 
== Technology ==
   
There are a variety of technologies for digitally acquiring the shape of a 3D object. A well established classification<ref>{{cite journal |author=Brian Curless |title=From Range Scans to 3D Models |journal=ACM SIGGRAPH Computer Graphics |volume=33 |issue=4 |pages=38–41 |month=November |year=2000 |doi=10.1145/345370.345399 }}</ref> divides them into two types: contact and non-contact 3D scanners. Non-contact 3D scanners can be further divided into two main categories, active scanners and passive scanners. There are a variety of technologies that fall under each of these categories.
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hhghggg[[File:Lidar P1270901.jpg|thumb|right|240px|This [[lidar]] scanner may be used to scan buildings, rock formations, etc., to produce a 3D model. The lidar can aim its laser beam in a wide range: its head rotates horizontally, a mirror flips vertically. The laser beam is used to measure the distance to the first object on its path.]]
 
=== Contact ===
 
[[File:9.12.17 Coordinate measuring machine.png|thumb|right|240px|A coordinate measuring machine with rigid perpendicular arms.]]
 
Contact 3D scanners probe the subject through physical touch, while the object is in contact with or resting on a [[Flatness (manufacturing)|precision flat]] [[surface plate]], ground and polished to a specific maximum of surface roughness. Where the object to be scanned is not flat or can not rest stably on a flat surface, it is supported and held firmly in place by a [[Fixture (tool)|fixture]].
 
 
The scanner mechanism may have three different forms:
 
* A carriage system with rigid arms held tightly in perpendicular relationship and each axis gliding along a track. Such systems work best with flat profile shapes or simple convex curved surfaces.
 
* An articulated arm with rigid bones and high precision angular sensors. The location of the end of the arm involves complex math calculating the wrist rotation angle and hinge angle of each joint. This is ideal for probing into crevasses and interior spaces with a small mouth opening.
 
* A combination of both methods may be used, such as an articulated arm suspended from a traveling carriage, for mapping large objects with interior cavities or overlapping surfaces.
 
 
A CMM ([[coordinate measuring machine]]) is an example of a contact 3D scanner. It is used mostly in manufacturing and can be very precise. The disadvantage of CMMs though, is that it requires contact with the object being scanned. Thus, the act of scanning the object might modify or damage it. This fact is very significant when scanning delicate or valuable objects such as historical artifacts. The other disadvantage of CMMs is that they are relatively slow compared to the other scanning methods. Physically moving the arm that the probe is mounted on can be very slow and the fastest CMMs can only operate on a few hundred hertz. In contrast, an optical system like a laser scanner can operate from 10 to 500&nbsp;kHz.
 
 
Other examples are the hand driven touch probes used to digitize clay models in computer animation industry.
 
 
=== Non-contact active ===
 
 
Active scanners emit some kind of radiation or light and detect its reflection or radiation passing through object in order to probe an object or environment. Possible types of emissions used include light, [[Non-Contact Ultrasound|ultrasound]] or x-ray.
 
 
==== Time-of-flight ====
 
[[File:Lidar P1270901.jpg|thumb|right|240px|This [[lidar]] scanner may be used to scan buildings, rock formations, etc., to produce a 3D model. The lidar can aim its laser beam in a wide range: its head rotates horizontally, a mirror flips vertically. The laser beam is used to measure the distance to the first object on its path.]]
 
   
 
The time-of-flight 3D laser scanner is an active scanner that uses laser light to probe the subject. At the heart of this type of scanner is a time-of-flight [[laser rangefinder]]. The laser rangefinder finds the distance of a surface by timing the round-trip time of a pulse of light. A laser is used to emit a pulse of light and the amount of time before the reflected light is seen by a detector is timed. Since the [[speed of light]] <math>c</math> is known, the round-trip time determines the travel distance of the light, which is twice the distance between the scanner and the surface. If <math>t</math> is the round-trip time, then distance is equal to <math> \textstyle c \! \cdot \! t / 2</math>. The accuracy of a time-of-flight 3D laser scanner depends on how precisely we can measure the <math>t</math> time: 3.3 [[picosecond]]s (approx.) is the time taken for light to travel 1 millimeter.
 
The time-of-flight 3D laser scanner is an active scanner that uses laser light to probe the subject. At the heart of this type of scanner is a time-of-flight [[laser rangefinder]]. The laser rangefinder finds the distance of a surface by timing the round-trip time of a pulse of light. A laser is used to emit a pulse of light and the amount of time before the reflected light is seen by a detector is timed. Since the [[speed of light]] <math>c</math> is known, the round-trip time determines the travel distance of the light, which is twice the distance between the scanner and the surface. If <math>t</math> is the round-trip time, then distance is equal to <math> \textstyle c \! \cdot \! t / 2</math>. The accuracy of a time-of-flight 3D laser scanner depends on how precisely we can measure the <math>t</math> time: 3.3 [[picosecond]]s (approx.) is the time taken for light to travel 1 millimeter.
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