function
three-dimensional scanner model (8)
three-dimensional scanner purpose is to create an object geometric surface point cloud (point cloud ), these interpolated points can be used to a surface shape of the object, the more dense point clouds to create more accurate models (this process is called reconstruction). If the surface of the color scanner can be obtained, it can be further pasting textures on the reconstructed surface, i.e., a so-called exit printed material (texture mapping).may be analogized to three-dimensional scanner of the camera, they are rendered conical sight, information gathering are limited within a certain range. The difference between them is that the camera captured the color information, the three-dimensional scanner measures the distance. Since the measured results contain information on depth, so often Video depth (depth image) or Video distance (ranged image) termed. Full
Due to the limited scanning range of the three-dimensional scanner, and therefore often need to change the relative position of the scanner and the object or objects placed on Turntable (turnable table), after several scan the object to guess Model. The plurality of one-sided model integration technology called video registration (image registration) or alignment (alignment), which involves more than a three-dimensional (3D-matching) method.
Technical
is classified as three-dimensional scanner contact (Contact) and two non-contact (non-contact), which can be divided into an active scan (active) passive scan (passive), under these categories and subdivided into a number of different techniques. Using visible light reach the video reconstruction method, also known as doing based on machine vision (vision-based) way, it is one of today's mainstream machine vision research.
contact scanning
contact 3D scanner calculated actual way through the depth of the surface of the touch object, such as a coordinate measuring machine (CMM, Coordinate Measuring Machine) that is typical contact three-dimensional scanner. This method is very precise, often used in engineering and manufacturing industry, however, because the object must be in contact, the analyte during the scanning process there may have been damage to the probe damage, and therefore not suitable for high-value objects such as ancient artifacts, relics, etc. the reconstruction work. In addition, compared to other methods of contact scanning takes a long time, today's fastest coordinate measuring machine to complete hundreds of measurements per second, and optical technologies such as laser scanners operate in the frequency per second and up to 10000-5 million times.
noncontact active scanning
Active scanning means additional energy is projected onto the object, to calculate three-dimensional information by means of the reflected energy. Common projected energy have generally visible light, high-energy beam, ultrasound and X-rays.
ToF (Time-of-Flight)
ToF (time-of-flight, or called 'flying time ranging') a 3D laser scanner is an active (active) scanner, which uses a laser light to detect the object. FIG i.e., light of a laser range finder (laser rangefinder) to a main ToF technique. This laser rangefinder determines the distance to the surface of the target instrument manner, the laser pulse measuring device is derived from emitted from the trip time conversion. I.e., a device emitting laser light pulses, the reflected laser beam hitting the surface, and then received by the signal detector within the instrument and the time recorded. Since the speed of light (speed of light) {\ displaystyle c} is a known condition, round trip time of the optical signal is converted into a distance signal to walk, and this distance is twice the distance from the surface to the instrument body, so if order {\ displaystyle t} is the round trip time of the optical signal, the optical signal traveling distance is equal to {\ displaystyle (c \ cdot t) / 2}. Apparent, ToF-style 3D laser scanner, which measurement accuracy is more time we can measure accurately {\ displaystyle t}, because about 3.3 picoseconds (Picosecond; picosecond) time left optical signal 1 mm.
a laser rangefinder laser signals each sent only to a single point distance measurement instrument. Thus, the scanner to scan the entire field of view (field of view), it is necessary that each of the laser signals emitted at different angles. The laser range finder section to achieve this through a horizontal rotation system itself or internal rotating mirror (rotating mirrors). Since lighter rotating mirror, fast scan ring switch, and high precision, is more widely used approach. Typical ToF formula laser scanner can measure from about 10,000 to 100,000 per target point.
triangulation (Triangulation)
triangulation 3D laser scanner, also belong to the active laser scanner to detect the situation of the environment . With respect to the distance measuring method, a method of triangulation 3D laser scanner emit a laser light when the fly to the DUT, and using the camera to find the laser spot on the DUT. As the analyte (ranging from 3D laser scanner triangle) different from the position of the laser spot in the camera picture also different. This technique is known as triangulation distance measuring method, because the laser spot, the camera, the laser itself constitutes a triangle. In this triangle, the distance of the laser and camera, and laser in a triangle point of view, we are known conditions. Camera through the screen position of the laser spot, we can determine the angle of the camera is located in the triangle. These three conditions can determine a triangle, and calculates the distance the analyte. In many cases, the laser stripe-shaped line to replace a single light spot of the laser, the laser stripe to analytes for scanning, greatly accelerate the whole process of measurement. National Research Council of Canada is one of association committed to the development of triangulation laser scanning technology (1978).
handheld laser (Handhold Laser)
to construct the hand-held laser scanner 3D graphics transmitted through the triangular distance measuring method: via handheld device, to analytes emits linear laser spot or a laser light. In the two or more detectors (or an electrical component coupled to the position sensing assembly) measured object surface to be measured from the laser to the handheld products, typically required by a particular reference point - typically a sticky, reflective patch - used as a scanner located in space and calibration used. These data obtained in the scanner, the computer will be imported by the software is converted into 3D models. Hand-held laser scanner, also typically integrated passive scan (visible light) data obtained (structure of the analyte, color distribution), to construct a more complete 3D model analyte.
structured light source (Structured Lighting)
to one or two dimensional images projected onto the measured object, according to the case of the strain image, it is determined measuring the surface shape thereof can be very fast scan, with respect to the measurement point probe, this method can measure a large area or a multi-point, it can be used for dynamic measurement.
modulated light (Modulated Lighting)
modulation light 3D scanner adjust the light intensity continuity in time, commonly used modulation mode is a periodic sine wave. Observation by means of the brightness change with the optical phase difference for each pixel of video, depth can be estimated distance. A laser light source can be modulated or projector, the laser light energy to achieve a high degree of accuracy, however, this method is quite sensitive to noise.
non-contact passive scanning
passive scanner itself does not emit any radiation (e.g., laser), but rather is measured by the test method of the reflective surface around the radiation to reach the desired effect. Since visible radiation in the environment, it is fairly easy to obtain and use, most of these types of scanners to detect visible light-based environment. However, compared to other visible light radiation, such as infrared, but also can be applied to this purpose. Because in most cases, passive scanning method does not require special hardware support standard too, such passive products are often quite cheap.
stereo method (Stereoscopic)
conventional stereoscopic imaging system using two cameras together, parallel to the focusing on an object to be reconstructed. This method is conceptually similar to human eyes by means of depth perceived video projected one above [1] (in fact, of course, the human brain to perceive the depth information of course many complex), two cameras known if the focal length distance from one another, the interception of about two pictures superimposed can succeed, the depth information can be derived quickly. This method must rely on a valid image analysis pixel matching (correspondence analysis), generally use block matching (block matching) or epipolar geometry (epipolar geometry) algorithms achieve.
using two cameras stereo method known as do Method binocular vision (binocular) , visual and another three (trinocular) extended using other methods more cameras.
color molding method (Shape from Shading)
BKP Horn et earlier proposed by researchers, using a video luminance pixel values are substituted into the pre-designed color solving the model, namely the solution of equations depth information. Since the equations in the unknowns more than limitation, so assumptions must be by means of more narrow set of solutions. For example, the surface may be added to the differential properties (differentiability), limiting the curvature (curvature constraint), smoothness (Smoothness) limitation and more accurate solution is obtained. After this method is derived from the stereo optical method Woodham.
perspective optics (Photometric Stereo)
Photometric molding method in order to compensate individual photos provided insufficient information, an optical stereo method using a multi-camera pictures, these pictures shooting angle is the same, wherein the difference of illumination light conditions. The simplest method using a three dimensional optical light source is irradiated from three different directions was measured, each time only one light source opening. Photo shooting after the completion of three integrated gradient vector and solving the model object surface (Gradients) in perfect optical diffuser (perfect diffusion), after integration of the vector field can be obtained three-dimensional model. This method does not apply to smooth approximates a Lambertian surface (Lambertian surface) of the object.
profilometry
Such a method is to use a series of contour lines constituting a three-dimensional molded object. When a portion of the surface of an object can not show on the contour line, after a three-dimensional reconstruction of lost information. Common way is to be tested was placed on a turntable motor which is rotated by a small angle after its video imaging, and then removing the background by a video processing techniques and removed contour lines, contour lines after collection of each angle can "draw" into a three-dimensional model.
user-assisted
Some methods require additional user information in the reconstruction process to provide, by means of the unique properties of the human visual system, the auxiliary program to complete the reconstruction.
these methods are based on the principle of photography photo, shooting a video for the same objects in order to calculate the three-dimensional information. Another similar approach is panoramic reconstruction (panoramic reconstruction), but all around the video shoot on the spot to enable it to reconstruct the scene environment.
Application
Reverse Engineering
Reverse engineering is a technical process, that is an objective product analysis and reverse research to interpret and draw the processing flow of product, organizational structure, functional performance specifications and other design elements to produce functionally similar, but not exactly the same product. Analysis of commercial and military hardware in the field of reverse engineering from. Its main purpose is, in production can not easily obtain the necessary information, the finished product directly from the analysis, design principles derived products. Reverse engineering might be mistaken for serious violations of intellectual property rights, but in practice, they may be protected by intellectual property owners. For example in the field of integrated circuits, if a company suspected of infringing intellectual property rights, you can use reverse engineering techniques to find evidence.
Cultural assets
The various objects may be recorded through the 3D scanning, as small as a variety of artifacts, works of art, ranging from historic buildings, neighborhoods and even whole buildings can be urban environment scan through digitization, as an application on the cultural assets can be divided into the following purposes:
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record appearance
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future based on the repair of
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entity copy
by reduction of the model of three-dimensional scanning of up to 99%, it surface ornamentation and features some of the details, but we also can quickly get volume and surface area of a heritage, its application of this technology direction, including digital archives of cultural retention, virtual heritage restoration assistance. In the restoration of cultural relics, some artifacts because of erosion, surface information has been blurred; when there have been mutilated relics were found, three-dimensional technology can be collected relics information into a data model that provides accurate data basis for the restoration of cultural relics.
Referring
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3D computer graphics
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3D computer graphics software
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computer vision
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laser rangefinder