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3D contact scanner
3D scanning technologies - what is 3D scanning and how does it work?
3D scanning is a technique used to capture the shape of an object using a 3D scanner. The result is a 3D file of the object which can be saved, edited, and even 3D printed. Many different 3D scanning technologies exist to 3D scan objects, environments, and people. Each 3D scanning technology comes with its own limitations, advantages, and costs.
Table of contents
Introduction
Laser triangulation 3D scanning technology
Structured light 3D scanning technology
Photogrammetry 3D scanning technology (photography)
Contact-based 3D scanning technology
Laser pulse-based 3D scanning technology
Introduction
The basic principle of 3D scanning is to use a 3D scanner to collect data about a subject. The subject can be:
- an object
- an environment (such as a room or even a landscape)
- a person (3D body scanning)
Some 3D scanners can simultaneously collect shape and color data. A 3D scanned color surface is called a texture.
3D scans are compatible with Computer-Aided Design (CAD) software and also 3D printing, after preparing the 3D model via specific software. A 3D scan can give a lot of information about the design of an object, in a process called reverse engineering.
3D scanners are powerful tools for professionals in several industries, such as automotive, aerospace, dental, and jewelry, as well as in more artistic applications such as video games, special effects, and animation movies. 3D scanning technologies rely on different physical principles and can be classified into the following categories:
- Laser triangulation: Projects a laser beam onto a surface and measures the deformation of the laser ray.
- Structured light: Measures the deformation of a light pattern when projected onto a surface to 3D scan the shape of the surface.
- Photogrammetry: Also called “3D scan from photographs”, this technology reconstructs a subject in 3D from 2D captures (photos) with computer vision and computational geometry algorithms.
- Contact-based 3D scanning technology: Relies on the sampling of several points on a surface, measured by a mechanical, optical, or physical probe.
- Laser pulse: Based on the Time of Flight (ToF) of a laser beam. The laser beam is projected onto a surface and recollected by a sensor. The time of travel of the laser between its emission and reception gives the surface’s geometrical information to the 3D scanner.
3D scanning technologies
Laser triangulation 3D scanning technology
Laser triangulation-based 3D scanners use either a laser line or a single laser point to scan across an object. First, the 3D scanner casts its laser onto the object. As the laser light reflects off of the 3D scanned object, its initial trajectory is modified and picked up by a sensor.
Then, based on this modified trajectory and thanks to trigonometric triangulation, the system can detect the laser’s deviation angle.
The calculated angle is directly linked to the distance from the object to the scanner. When the 3D scanner collects enough distances, it is capable of mapping the object’s surface to recreate it in 3D.
The main advantages of the laser triangulation technology for 3D scanning are its high resolution and accuracy.
One downside to laser triangulation technology is how sensitive it is to the properties of object’s surface; very shiny and/or transparent and/or dark surfaces are particularly problematic.
Structured light 3D scanning technology
Structured light 3D scanners use trigonometric triangulation but do not rely on a laser. Instead, they project a series of linear patterns onto the object. The system is then able to examine the edges of each line in the pattern and how the lines are deformed and to calculate the distance from the scanner to the object’s surface.
The projected structured light used for 3D scanning can be white or blue and generated by numerous types of projectors, such as Digital Light Processing (DLP) technology. The projected pattern is usually a series of light rays but can also be a randomized dot matrix.
The main advantages of structured light technology for 3D scanning are its speed and resolution, and its non-harmful light can be used for 3D body scanning.
However, structured light 3D scanners are sensitive to lighting conditions and have trouble working outdoors in broad daylight.
Photogrammetry 3D scanning technology (photography)
Photogrammetry is the science of making measurements from photographs, especially for recovering the exact positions of surface points. Photogrammetry is based on a mix of computer vision and powerful computational geometry algorithms.
The principle of photogrammetry is to analyze several photographs of a static subject, taken from different viewpoints, and to automatically detect pixels corresponding to a unique physical point.
This 3D scanning technology’s main challenge is to examine tens or hundreds of photos and thousands of points with high accuracy. To run such photogrammetry algorithms, a very powerful computer is required.
The main advantages of photogrammetry 3D scanning technology are its acquisition speed and ability to pick up colors and textures. Photogrammetric technology is also capable of reconstructing subjects at large scales, such as landscapes or monuments photographed from the ground or from the air, by a photography drone, for example.
The quality of the results generated by photogrammetry technology is dependent on the resolution of the input photographs. This technology can also be quite slow, depending on your software and PC setup.
Contact-based 3D scanning technologyContact-based 3D scanning is also known as digitizing. This 3D scanning technology implies a contact-based form of 3D data collection.
Contact 3D scanners probe the subject via physical touch, while the object is firmly held in place. A touching probe is moved along the surface to record 3D information. The probe is sometimes attached to an articulated arm capable of collecting all its respective configurations and angles for more precision.
Some specific configurations of contact-based 3D scanners are called Coordinate Measuring Machines (CMM).
Contact 3D scanning is widely used to perform quality control after fabrication or during maintenance operations. The main advantages of the contact technology for 3D scanning are its precision and ability to 3D scan transparent or reflective surfaces.
The downsides of contact 3D scanning technology include its slow speed and inability to work with organic, freeform shapes.
Laser pulse-based 3D scanning technology
Laser pulse-based 3D scanners, also known as Time-of-Flight scanners or Lidar laser 3D scanners, measure how long a casted laser takes to hit an object and come back.
Since the speed of light is exactly known, the time it takes for the laser to come all the way back gives the exact distance between the 3D scanner and the object. In order to precisely measure the distance, the 3D scanner computes millions of laser pulses with accuracy up to the picosecond (1 picosecond equals 0.000000000001 seconds!).
Since each measure only collects one point, the 3D scanner needs to cast its laser 360 degrees around that point. To do so, the 3D scanner is usually fitted with a mirror that changes the orientation of the laser.
Time-of-Flight 3D scanners encompass both laser pulse and phase shift lasers. Phase shift laser 3D scanners are a sub-category of laser pulse 3D scanners. In addition to pulsing the laser, phase shift systems also modulate the power of the laser beam. Phase shift lasers offer better overall performance.
The main advantage of laser pulse 3D scanners is their ability to 3D scan very big objects and environments.
They are, however, quite slow.
Laser pulse technology is often used by terrestrial laser 3D scanners, which are mainly destined for land surveying or to 3D scan entire buildings. Some laser pulse 3D scanners also incorporate dynamic SLAM algorithms to enhance their ability to recognize their surroundings.
Types of 3D Scanning Technologies and 3D Scanners
3D laser scanning is a way to capture a physical object’s exact size and shape into the computer world as a digital 3-dimensional representation. This technique captures information like the complex geometry, intrigue shape, colorized texture, and other details of the 3D object that is scanned.
A 3D scanner collects information about the object being scanned as well as the environment (e.g. room) in which the object is present. If, a person is sitting beside the object that can also be 3D scanned.
3D scanners essentially create a digital copy of a real-world object. This digital copy or the 3D file can then be edited and 3D printed as per the user’s requirements.
Also, a 3D file can be used for further 3D modeling processes. Generally, in this 21st-century Engineers are using this technology for reverse engineering processes. 3D scanner files are generally compatible with CAD software and 3D printing slicer software.
A single scan is not enough to re-create a complete model of the object being scanned. Normally, hundreds of scans are necessary to capture all of the information from various sides and angles. All of these scans than have to be integrated through a common reference system known as alignment/registration. Finally, the individual scans are merged to re-create the final model. This entire process of bringing together the individual scans and merging them is known as a 3D scanning pipeline.
3D laser scanning technology largely classified into the following methods:
Time of Flight, Triangulation, Phase shift, Stereo.
Different types of 3d scanning methods and the principles they are based on are as follows:
1.
LASER triangulation 3D scanning technology.
2. Structured light 3D scanning technology.
3. Photogrammetry.
4. Contact-based 3D scanning technology.
5. LASER pulse-based 3D scanning technology.
1. Laser-based 3D Scanners
Laser-based 3D scanners use a process called trigonometric triangulation to accurately capture a 3D shape as millions of points. Laser scanners work by projecting a laser line or multiple lines onto an object and then capturing its reflection with a single sensor or multiple sensors.
The sensors are located at a known distance from the laser's source. Accurate point measurements can then be made by calculating the reflection angle of the laser light. Laser scanners are very popular and come in many designs.
They include handheld portable units, arm based, CMM based, long-range, and single point long-range trackers.
Benefits of 3D Laser Scanners
1. Scan tough surfaces, such as shiny or dark finishes
2. Lesser sensitive: to changing light conditions and ambient light
3. Portable
4. Simple design, easy to use, and low cost.
2. Projected or Structured Light 3D Scanners
Historically known as “white light” 3D scanners, mainly structured light 3D scanners today use a blue or white LED projected light.
These 3D scanners project a light pattern consisting of bars, blocks, or other shapes onto an object.
The 3D scanner has one or more sensors that look at the edge of those patterns or structural shapes to determine the object's 3D shape.
Using the same trigonometric triangulation method as laser scanners the distance from the sensors to the light source is known. Structured light scanners can be tripod mounted or handheld.
Benefits of Structured light 3D Scanners
1. Very fast scan times –as fast as 2 seconds per scan
2.
Large scanning area –as large as 48 inches in a single scan
3. High resolution –as high as 16 million points per scan and 16-micron (.00062”) point spacing
4. Very high accuracy –as high as 10 microns (.00039”)
5. Versatile –multiple lenses to scan small to large parts in a single system
6. Portable –handheld systems are very portable
7. Eye safe for 3D scanning of humans and animals
8. Various price points from low cost to expensive depending on resolution and accuracy
3. Medium and Long-Range 3D Scanners
Long-range 3D scanners come in two major formats-Pulse based and phase shift–both of which are well suited for large objects such as buildings, structures, aircraft, and military vehicles. Phase shift 3D scanners also work well for medium-range scan needs such as automobiles, large pumps, and industrial equipment. These scanners capture millions of points by rotating 360 degrees while spinning a mirror the redirects the laser outward towards the object or areas to be 3D scanned.
Laser pulse-based 3Dscanners
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. Thus, if the length of time laser takes to reach an object and reflect back to a sensor is known, the distance from the sensor to the object is known. 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 3D Scanners
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 sent out and returned to the sensor.
Phase shift measurements are typically more accurate and quieter but are not as flexible for long-range scanning as pulse-based 3D scanners. Laser pulse-based 3D scanners can scan objects up to 1000m away while phase shift scanners are better suited for scanning objects up to 300m or less.
Benefits Long Range 3D Scanners
1. 3D Scan millions of points in a single scan –up to 1 million points per second
2. Large scanning area more than 1000 Sq. meters
3. Good accuracy and resolution based on object size
4. Non-contact to safely scan all types of objects
5. Portable
4. Photogrammetry
This technology is quite simple. It involves stitching together photographs of an object taken from different angles. The photos are taken using a camera or even your smartphone with specific camera settings, while the stitching of those photos is done by special software. The software identifies pixels that correspond to the same physical point and brings pictures together accordingly.
Parameters like the focal length of the lens and its distortion need to be fed into the software by the user to create an accurate model. Photogrammetry is so simple that you can pick up your phone right now and start taking pictures.
The big advantage of using photogrammetry is its accuracy level and the speed with which the data of an object is acquired. The downside with this technique is the time it takes to run the image data through the software and the sensitivity of the end result to the resolution of the photographs. You need to have a good camera with high resolution and DPI to get a good end result.
We can simulate these photos with many software such as Reality capture, Blender, Mushroom, 3DF Zephyr, Agisoft Metashape, etc.
5. Contact scanning
This scanning method involves physical contact of a probe onto the surface of the object being scanned. First, the object is firmly held in place so that it does not move. Then, the touching probe is moved all over the object in order to collect the details of the object and all the 3D information that is necessary to create a digital file.
Enough points on the surface need to be sampled to create an accurate model. Sometimes, an articulated arm is used to control the touching probe and capture multiple angles/configurations with a high level of precision.
Since contact scanning involves actual physical contact with the surface of the object being scanned, even transparent and reflective surfaces can be accurately scanned using this method. This is the major benefit of this technique over other scanning technologies, which as pointed out above, are incapable of scanning such surfaces.
The disadvantage with contact 3D scanning is its slow speed. Running the touching probe through all sections of an object in order to collect all the 3D information takes time.
Contact 3D scanning is interestingly used to perform quality control in industrial fabrication. Parts that have been newly fabricated can be checked for any deformations or damages using contact scanning.
How does a 3d scanner work? Device, principle and technologies of 3D scanning
3D scanner is a stationary or small hand-held device for scanning objects with complex spatial geometry.
Simple scanners process images in a plane, while 3d scans physical volumetric objects, displaying information as a polygonal model or a cloud of points. Three-dimensional scanning devices are used in medicine (dentistry, plastic surgery, making prostheses, organ models, etc.), for creating computer games, in the film industry, design, architecture, engineering, for designing industrial parts, cars, for reconstructing objects in archeology. Scanners analyze and digitally recreate a three-dimensional model of an object, its shape and color with a high degree of detail, working in different conditions (with insufficient visibility, in the dark, with vibration), with any materials, provide the desired format of output information for software for work with her on the computer.
How does a 3D scanner work?
The principle of operation of the 3d scanner is the ability of the device to determine the distance to an object, convert the received data into a digital image (three-dimensional model), and transfer it to a computer.
The scanner determines the coordinates of points in space on the surface of the processed object, analyzes them, and forms a detailed digital model. Cameras, lasers, rangefinders, devices for illumination are involved in its work.
3D scanning technologies
- Contact (contacts with the object).
- Non-contact (without object contact). These are the most promising and new technologies that allow you to create models of objects simply by directing a laser beam, light, waves at them. The scanner is applied at a distance and is able to create a copy of a hard-to-reach object without physical contact with it.
Non-contact 3d scanners
The two most common scanning technologies are optical (passive and radiation) and active laser.
Active emission principle
Scanner emits structured, intermittent light, laser triangulation.
A laser beam, a beam of light generated in a special way (diodes, lamp flashes), and waves are directed to the object under study. Based on the analysis of their reflection and position, a three-dimensional copy of the object is formed.
Passive radiation principle
Do not emit anything, analyze the light or infrared (thermal) radiation of an object. Work like a human eye;
Photometric non-contact passive 3d scanning technology
Scanners from this group are represented on the market by the XYZprinting model. These are quite compact simple models that have only basic 3D scanning functions.
Pluses: reasonable price and compactness.
Device
Passive 3d scanner device (on the example of the specified model): housing, one compact camera, USB cable for connecting to a computer and transferring the image of the scanned object to it. Scanner without stand, manual, made in the form of a stapler.
How it works
A light-sensitive camera captures light from an object, processes it, and forms a three-dimensional model, exporting it to a computer. The user can have two modes of operation: scanning a person or objects. To get started, you need to install the software on your computer, connect the device to it via a USB cable, select the operating mode, press the button on the scanner and, slowly swiping it in front of the object, scan.
How the technology works
The device works with passive scanning photometric technology without any radiation and projection onto the object. The work is carried out with a slightly improved simple optical camera that captures visible light. The disadvantage is that if the lighting is insufficient, the object needs to be additionally illuminated.
Scanning is performed using the so-called silhouette method. It reproduces the contours of an object based on a sequence of frames captured by a video camera swept around the object against a well-contrasted background.
Stereoscopic non-contact passive 3d scanning system
Models with non-contact passive scanning technology
This type of device is represented by 3D Systems Sense, 4D Dynamics Gotcha models.
Device and principle of operation of a 3d scanner based on the non-contact passive scanning system
Devices are equipped with two cameras and an infrared sensor. The 3D Systems Sense scanner is made in the form of a stapler, it is a compact handheld device, it can be used with a tripod, in Gotcha (with a tripod and a handle), it is included. The principle of operation is passive optical. In both cases, power and data transfer is carried out via a USB cable. The devices have standard modes: scanning a person and an object.
Scan technology
The camera uses this technology to detect infrared (thermal) radiation and normal light reflected from an object.
The systems are stereoscopic, that is, they use two cameras. The device compares frames, based on small comparisons of differences between them, determines the distance at each point of the image and recreates the object in digital form.
3d scanners with laser active scanning
This group of devices is represented by the following scanner models: 3D Systems iSense, DAVID Starter-Kit ver.2, MakerBot Digitizer.
Device
Devices have two lasers and a camera. It should be noted that the laser safety of gadgets corresponds to level I, which is completely safe for the eyes. The iSense scanner is designed to work only with the iOS operating system and with Apple iPad above 4 generations. It is made in a compact case, which is installed on a mobile gadget and connected to it with a USB cable, the battery lasts for 4 hours of its operation. It attaches like a webcam, scans and immediately displays the image on the iPad.
Models
DAVID Starter-Kit ver.2 3D scanner device: webcams and laser sensors with automatic adjustment function. The device comes with a tripod and tripod.
Maker Bot Digitizer is somewhat different in design from the previous model. The body of the scanner is made as a pedestal, one part of which is a rotating platform, the other is equipped with two lasers on the sides and a camera in the middle. They scan an object located on the site.
How technology works
Let's describe how a 3D scanner works. Laser scanning is based on the triangulation method. This is an active scan tool. It uses laser beams by projecting it onto an object. The laser processes the surface of the object, its points are fixed on its different parts. The camera captures the laser dots on it, the angle of displacement of the laser beam and transmits the data to a computer with the appropriate software, which forms the object in digital form.
The scanning technology is called “triangulation”, because the triangle of functional elements of the device is involved in the work: the laser point on the object, its emitter, and the camera. In most cases, the dot is formed by a laser streak or spot passing over the surface of the object.
Structured light 3d scanning technology
Models that use structured or intermittent light technology in their work: DAVID SLS-2, RangeVision Smart, RangeVision Standard Plus, RangeVision Advanced, RangeVision Premium. A separate group includes manual Artec Spider, Artec Eva, Artec Eva Lite.
Device
The main functional elements of these devices are cameras and a light source that structures it in a special way and directs it to the scanned object. In the DAVID SLS-2 model, a video projector serves as a light source. These are mounted on a tripod with a tripod, which are included.
This allows you to set up and calibrate instruments, install them in different positions and securely fix them, reducing vibration. Light sources in devices are halogen lamps, diodes, video projector.
Artec Spider, Artec Eva, Artec Eva Lite are made in a compact body with an iron-like handle. The handle has control buttons and outputs for interface and power cords. At the bottom there is also a hole for standard photo tripods and legs for fixing the device on the surface. 3d scanner device has the following. From the bottom it is equipped with a 3D camera (there are three of them in Artec Spider) with increased resolution, from the top of the device - a flash (projector) of structured illumination, a central color texture camera in the middle, along with light sources in the form of 6 or 12 diode bulbs. All light sources have white radiation. The device comes with a standard mini-USB interface cable and a power cable. Additionally, you can buy a rechargeable battery.
How the technology works
Such devices are also called structural-light 3D scanners. The scanning technology is similar to laser triangulation (light, emitter, camera). The important thing is that they can work without markers - the object does not need to be glued with a lot of markers and marks. The essence of structured light technology lies in projecting a pattern of light onto an object and fixing and analyzing its deformation. The luminous flux is projected onto the object by several types of light sources: LCD, video projector, diodes, halogen lamps.
The camera detects shifts in the light pattern that enters its field of view and looks like moving lines of light on the surface of an object. It calculates and analyzes the distance from each illuminated point of the object and thus forms its detailed digital copy. The advantage of Light 3D scanners is speed and high accuracy. They scan not one or several points, but simultaneously a cluster of points or the entire field of view at once.
Everything about 3D scanners: from varieties to applications
The 3D scanner is a special device that analyzes a specific physical object or space in order to obtain data about the shape of the object and, if possible, its appearance (for example, color). The collected data is then used to create a digital three-dimensional model of this object.
To create 3D-scanner allows several technologies at once, differing from each other in certain advantages, disadvantages, as well as cost. In addition, there are some restrictions on the objects that can be digitized. In particular, there are difficulties with objects that are shiny, transparent or have mirror surfaces.
Don't forget that 3D data collection is also important for other applications. So, they are needed in the entertainment industry to create films and video games. Also, this technology is in demand in industrial design, orthopedics and prosthetics, reverse engineering, prototyping, as well as for quality control, inspection and documentation of cultural artifacts.
Functionality
The purpose of the 3D Scanner is to create a point cloud of geometric patterns on the surface of an object. These points can then be extrapolated to recreate the shape of the object (a process called reconstruction). If color data were obtained, then the color of the reconstructed surface can also be determined.
3D scanners are a bit like regular cameras. In particular, they have a cone-shaped field of view, and they can only receive information from surfaces that have not been darkened. The difference between these two devices is that the camera transmits only information about the color of the surface that fell into its field of view, but the 3D scanner collects information about the distances on the surface, which is also in its field of view. Thus the "picture" obtained with of the 3D scanner, describes the distance to the surface at each point in the image. This allows you to determine the position of each point in the picture in 3 planes at once.
In most cases, one scan is not enough to create a complete model of the object. Several such operations are required. As a rule, a decent number of scans from different directions will be needed in order to obtain information about all sides of the object. All scan results must be normalized to a common coordinate system, a process called image referencing or alignment, before a complete model is created. This whole procedure from a simple map with distances to a full-fledged model is called a 3D scanning pipeline.
Technology
There are several technologies for digitally scanning a mold and creating a 3D model of a object. However, a special classification has been developed that divides the 3D scanners into 2 types: contact and non-contact. In turn, non-contact 3D scanners can be further divided into 2 groups - active and passive. Several technologies can fall under these categories of scanning devices.
Coordinated-measuring machine with two fixed mutually perpendicular measuring hands
Contact 3D scanners Contact Summarizers on a precision surface plate, ground and polished to a certain degree of surface roughness. If the scanned object is uneven or cannot lie stably on a horizontal surface, then a special vise will hold it. The scanner mechanism comes in three different forms: CMM (Coordinate Measuring Machine) is a prime example of the Contact 3D Scanner . They are used mainly in manufacturing and can be ultra-precise. The disadvantages of CMM include the need for direct contact with the surface of the object. Therefore, it is possible to change the object or even damage it. This is very important if thin or valuable items such as historical artifacts are being scanned. Another disadvantage of CMM over other scanning methods is slowness. Moving the measuring arm with the probe in place can be very slow. The fastest result of CMM operation does not exceed a few hundred hertz. At the same time, optical systems, for example, a laser scanner, can operate from 10 to 500 kHz. Another example is hand-held measuring probes used to digitize clay models for computer animation. The Lidar device is used to scan buildings, rocks, etc., which makes it possible to create 3D models of them. The Lidar laser beam can be used in a wide range: its head rotates horizontally, and the mirror moves vertically. The laser beam itself is used to measure the distance to the first object in its path. Non-contact active scanners Active scanners use certain types of radiation or just light and scan an object through the reflection of light or the passage of radiation through an object or medium. These devices use light, ultrasound, or x-rays. Time-of-Flight Scanners Time-of-Flight Laser Scanner The 3D scanner is an active scanner that uses a laser beam to examine an object. This type of scanner is based on a time-of-flight laser range finder. Triangulation scanners Two positions of the object are shown. A point cloud is created using triangulation and a laser stripe. Triangulation laser scanners 3D scanners are also active scanners that use a laser beam to probe an object. Like the time-of-flight 3D scanners, triangulation devices send a laser at the scanned object, and a separate camera captures the location of the point where the laser hit. Depending on how far the laser travels across the surface, the dot appears at different locations in the camera's field of view. Advantages and disadvantages of scanners Both time-of-flight and triangulation scanners have their own strengths and weaknesses, which determines their choice for each specific situation. As for triangulation rangefinders, the situation is exactly the opposite. Their range is only a few meters, but the accuracy is relatively high. Such devices can measure distance with an accuracy of tens of micrometers. The study of the edge of an object negatively affects the accuracy of the TOF scanners. The laser pulse is sent one, and is reflected from two places at once. The coordinates are calculated based on the position of the scanner itself, and the average value of the two reflections of the laser beam is taken. At 10,000 dots per second, low resolution scanners can do the job within seconds. But for scanners with high resolution, you need to do several million operations, which will take minutes. It should be borne in mind that the data may be distorted if the object or the scanner moves. So, each point is fixed at a certain point in time in a certain place. If the object or scanner moves in space, then the scan results will be false. That's why it's so important to mount both the object and the scanner on a fixed platform and keep the possibility of vibration to a minimum. It is also worth considering the fact that when scanning in one position for a long time, a slight movement of the scanner may occur due to temperature changes. If the scanner is mounted on a tripod and one side of the scanner is exposed to strong sunlight, then the tripod will expand and the scan data will gradually distort from one side to the other. However, some laser scanners have built-in compensators that counteract any movement of the scanner during operation. Conoscopic holography In the conoscopic system, a laser beam is projected onto the surface of an object, after which the beam is reflected along the same path, but through a conoscopic crystal, and is projected onto a CCD (charge-coupled device). The result is a diffraction pattern from which frequency analysis can be used to determine the distance to the surface of an object. Handheld laser scanners Handheld laser scanners create a 3D image using the triangulation principle described above. A laser beam or stripe is projected onto an object from a hand-held emitter, and a sensor (often a CCD or position-sensitive detector) measures the distance to the surface of the object. The data is collected relative to the internal coordinate system and therefore, to obtain results, if the scanner is in motion, the position of the device must be accurately determined. This can be done using basic features on the scanned surface (adhesive reflective elements or natural features) or using the external tracking method. The latter method often takes the form of a laser tracker (providing a position sensor) with a built-in camera (to determine the orientation of the scanner). Scan data is collected by a computer and recorded as points in 3D space, which after processing are converted into a triangulated grid. The computer-aided design system then creates a model using a non-uniform rational B-spline, NURBS (a special mathematical form for creating curves and surfaces). Handheld laser scanners can combine this data with passive visible light sensors that capture surface texture and color to create or reverse engineer a complete 3D Models . Structured Light The grid is projected onto the object using a liquid crystal projector or other constant light source. The advantage of the Structured Light 3D Scanners is their speed and accuracy. Instead of scanning one point at a time, structured scanners scan several points at the same time or the entire field of view at once. Scanning the entire field of view takes a fraction of a second, and the generated profiles are more accurate than laser triangulations. This completely solves the problem of data corruption caused by motion. In addition, some existing systems are capable of scanning even moving objects in real time. For example, the VisionMaster, a 3D scanning system, has a 5-megapixel camera, so each frame contains 5 million dots. Real-time scanners use digital edge projection and a phase-shifting technique (one of the techniques for applying structured light) to capture, reconstruct and create a high-density computer model of dynamically changing objects (such as facial expressions) at 40 frames per second. A new type of scanner has recently been created. Various models can be used in this system. The frame rate for capturing and processing data reaches 120 frames per second. This scanner can also process individual surfaces. For example, 2 moving hands. Using the binary defocusing method, the shooting speed can reach hundreds or even thousands of frames per second. Modulated light When using the 3D scanners based on modulated light, the light beam directed at the object is constantly changing. Often the change of light passes along a sinusoid. The camera captures the reflected light and determines the distance to the object, taking into account the path that the light beam has traveled. Volumetric techniques Medical Computed tomography (CT) is a special medical imaging technique that creates a series of three-dimensional x-ray images of an object's interior. Magnetic resonance imaging works on a similar principle - another imaging technique in medicine, which is distinguished by a more contrast image of the soft tissues of the body than CT. Therefore, MRI is used to scan the brain, the musculoskeletal system, the cardiovascular system, and to search for oncology. These techniques produce volumetric voxel models that can be rendered, modified, and transformed into a traditional 3D surface using isosurface extraction algorithms. Production Although MRI, CT or microtomography are more widely used in medicine, they are also actively used in other areas to obtain a digital model of an object and its environment. Non-contact passive scanners Passive scanners do not emit light, instead they use reflected light from the surrounding area. Most scanners of this type are designed to detect visible light, which is the most accessible form of ambient radiation. Other types of radiation, such as infrared, may also be involved. Passive scanning methods are relatively cheap, because in most cases they do not need special equipment, a conventional digital camera is enough. Photometric systems typically use a single camera that captures multiple frames in all lighting conditions. Silhouette techniques use contours from successive photographs of a three-dimensional object against a contrasting background. These silhouettes are extruded and transformed to get the visible skin of the object. However, this method does not allow you to scan the recesses in the object (for example, the inner cavity of the bowl). There are other methods that are based on the fact that the user himself discovers and identifies some features and shapes of the object, based on many different images of the object, which allow you to create an approximate model of this object. Such methods can be used to quickly create a three-dimensional model of objects of simple shapes, for example, a building. You can do this using one of the software applications: D-Sculptor, iModeller, Autodesk ImageModeler or PhotoModeler. This 3D scan is based on the principles of photogrammetry. Reconstruction From point clouds The point clouds generated by the 3D Scanners can be used directly for measurement or visualization in the field of architecture and engineering. These CAD models do not simply describe the shell or shape of an object, but they also enable design intent (that is, critical features and their relationship to other features) to be realized. An example of design intent that is not expressed in form would be the ribbed bolts of a brake drum, which should be concentric with the hole in the center of the drum. There are several approaches to get a parametric CAD model. Some involve only exporting a NURBS surface, leaving the CAD engineer to complete the modeling (Geomagic, Imageware, Rhino 3D). Others use the scan data to create an editable and verifiable function model that can be fully imported into CAD with an intact fully functional tree, providing a complete fusion of shape and design intent of the CAD model (Geomagic, Rapidform). However, other CAD applications are powerful enough to manipulate a limited number of points or polygonal models in a CAD environment (CATIA, AutoCAD, Revit). From the 2D slice set 3D reconstruction of the brain or eyeballs based on CT results is performed using DICOM images. CT, industrial CT, MRI or microCT scanners do not create a point cloud, but 2D slices (referred to as a “tomogram”) that are superimposed on each other, resulting in a kind of 3D model. There are several ways to do this scan, depending on the desired result: Application Material Handling and Manufacturing 3D Laser Scanning describes a general way to measure or scan a surface using laser technology. It is used in several areas at once, differing mainly in the power of the lasers that are used and the results of the scan itself. Low laser power is needed when the scanned surface should not be influenced, for example, if it only needs to be digitized. Confocal or 3D laser scanning are methods that provide information about the scanned surface. Another low power application involves a projection system that uses structured light. It is applied to solar panel plane metrology involving voltage calculation with a throughput of more than 2,000 plates per hour. The laser power used for laser scanning of industrial equipment is 1W. The power level is typically 200mW or less. Construction industry Benefits of 3D scanning Creating a 3D model through scanning has the following benefits: Entertainment 3D scanners are actively used in the entertainment industry to create digital 3D models in film and video games. If the model being created has a counterpart in the real world, then scanning will allow you to create a three-dimensional model much faster than developing the same model through 3D modeling. Quite often, artists first sculpt a physical model, which is then scanned to get a digital equivalent, instead of creating such a model on a computer. Reverse engineering Reverse engineering of mechanical components requires a very precise digital model of the objects to be recreated. This is a good alternative to converting many points of a digital model to a polygon mesh, using a set of NURBS flat and curved surfaces, or, ideally for mechanical components, creating a 3D CAD model. A 3D scanner can be used to digitize objects that freely change shape. As well as the prismatic configuration, for which a coordinate measuring machine is usually used. This will allow you to determine the simple dimensions of the prismatic model. This data is further processed by special programs for reverse engineering. 3D printing 3D scanners are also actively used in the field of 3D printing, as they allow you to create fairly accurate 3D models of various objects and surfaces in a short time, suitable for further refinement and printing. In this area, both contact and non-contact scanning methods are used, both methods have certain advantages. Cultural heritage An example of copying a real object through 3D scanning and 3D printing. There are many research projects that have been carried out using the scanning of historical sites and artifacts to document and analyze them. The combined use of 3D scanning and 3D printing makes it possible to replicate real objects without the use of a traditional plaster cast, which in many cases can damage a valuable or delicate cultural heritage artifact. The sculpture of the figure on the left was digitized using a 3D scanner, and the resulting data was converted in the MeshLab program. The resulting digital 3D model was printed using a rapid prototyping machine that allows you to create a real copy of the original object. Michelangelo There are many research projects that have been carried out using the scanning of historical sites and artifacts to document and analyze them. In 1999, 2 different research groups started scanning Michelangelo's statues. Stanford University, along with a team led by Mark Levoy, used a conventional laser triangulation scanner built by Cyberware specifically to scan Michelangelo's statues in Florence. In particular, the famous David, "Slaves" and 4 more statues from the Medici chapel. Scanning is performed with a dot density of 0.25 mm, sufficient to see the traces of Michelangelo's chisel. Such a detailed scan involves obtaining a huge amount of data (about 32 gigabytes). It took about 5 months to process them. Around the same time, a research group from IBM was working, led by H. Raschmeyer and F. Bernardini. They were tasked with scanning the Florentine Pieta sculpture to obtain both geometric data and color information. The digital model obtained from a Stanford University scan was fully used in 2004 to further restore the statue. Medical applications CAD/CAM 3D scanners are widely used in orthopedics and dentistry to create a 3D patient shape. Quality assurance and industrial metrology Digitization of real world objects is of great importance in various fields of application. 3D scanning is very actively used in industry to ensure product quality, for example, to measure geometric accuracy. Predominantly all industrial processes such as assembly are quite complex, they are also highly automated and are usually based on CAD (computer-aided design data).
This mechanism is ideal for probing recesses or interior spaces with a small inlet. 
In turn, the laser rangefinder determines the distance to the surface of the object, based on the time of flight of the laser back and forth. The laser itself is used to create a pulse of light, while the detector measures the time until the light is reflected. Given that the speed of light (c) is a constant value, knowing the time of flight of the beam back and forth, you can determine the distance over which the light has moved, it will be twice the distance between the scanner and the surface of the object. If (t) is the round-trip flight time of the laser beam, then the distance will be (c*t\2). Laser beam time-of-flight accuracy of the 3D scanner depends on how accurately we can measure the time itself (t): 3.3 picoseconds (approximately) is needed for the laser to overcome 1 millimeter.
The laser range finder measures the distance of only one point in a given direction. Therefore, the device scans its entire field of view in separate points at a time, while changing the direction of scanning.
You can change the direction of the laser rangefinder either by rotating the device itself, or using a system of rotating mirrors. The latter method is often used, because it is much faster, more accurate, and also easier to handle. For example, time-of-flight 3D scanners can measure distance from 10,000 to 100,000 points in one second.
TOF devices are also available in 2D configuration. Basically, this applies to time-of-flight cameras. 
This technology is called triangulation because the laser dot, the camera and the laser emitter itself form a kind of triangle. The length of one side of this triangle is known - the distance between the camera and the laser emitter. The angle of the laser emitter is also known. But the camera angle can be determined by the location of the laser dot in the field of view of the camera. These 3 indicators completely determine the shape and size of the triangle and indicate the location of the corner of the laser point. In most cases, to speed up the process of obtaining data, a laser strip is used instead of a laser dot. Thus, the National Research Council of Canada was among the first scientific organizations that developed the basics of triangulation laser scanning technology back in 1978 year. 
The advantage of time-of-flight devices is that they are optimally suited for operation over very long distances up to several kilometers. They are ideal for scanning buildings or geographic features. At the same time, their disadvantages include measurement accuracy. After all, the speed of light is quite high, so when calculating the time it takes for the beam to overcome the distance to and from the object, some flaws (up to 1 mm) are possible. And this makes the scan results approximate. 
This causes the point to be defined in the wrong place. When using scanners with high resolution, the chances that the laser beam hits the exact edge of the object increase, but noise will appear behind the edge, which will negatively affect the scan results. Scanners with a small beam can solve the edge scanning problem, but they have limited range, so the beam width will exceed the distance. There is also special software that allows the scanner to perceive only the first reflection of the beam, while ignoring the second. 
Therefore, scanning objects in motion is practically impossible. Recently, however, there has been active research on how to compensate for the effect of vibration on data corruption. 
The main advantage of conoscopic holography is that only one beam path is needed to measure the distance, which makes it possible to determine, for example, the depth of a small hole. 
You can also use photogrammetry, provided by 3 cameras, which gives the scanner six degrees of freedom (the ability to make geometric movements in three-dimensional space). Both techniques typically use infrared LEDs connected to the scanner. They are observed by cameras through filters that ensure the stability of ambient lighting (reflecting light from different surfaces). 
A camera positioned just to the side of the projector captures the shape of the network and calculates the distance to each point in the field of view.
Structured light scanning is still an active area of research, with quite a few research papers devoted to it each year. Ideal maps are also recognized as useful as structured light patterns that can solve matching problems and allow errors to be corrected as well as detected. 
Modulated light allows the scanner to ignore light from sources other than the laser, thus avoiding interference. 
This is important, for example, for non-destructive testing of materials, reverse engineering or the study of biological and paleontological samples.
Stereoscopic systems involve the use of 2 video cameras located in different places, but in the same direction. By analyzing the differences in the images of each camera, you can determine the distance to each point in the image. This method is similar in principle to human stereoscopic vision. 
These methods attempt to transform the object model in order to reconstruct the surface for each pixel. 
In addition, this technique is in some ways similar to panoramic photography, except that the photographs of the object are taken in three-dimensional space. Thus, it is possible to copy the object itself, rather than taking a series of photos from one point in three-dimensional space, which would lead to the reconstruction of the object's environment.
However, most applications use non-homogeneous rational B-spline, NURBS, or editable CAD models (also known as solid models) instead of 3D polygonal models.
At the same time, such models are quite « heavy" (accommodate a large amount of data) and are quite difficult to edit in this format. Reconstruction into a polygonal model involves searching and combining neighboring points with straight lines until a continuous surface is formed. For this, you can use a number of paid and free programs (MeshLab, Kubit PointCloud for Au toCAD, 3D JRC Reconstructor, ImageModel, PolyWorks, Rapidform, Geomagic, Imageware, Rhino 3D, etc.). 
Surface models are editable, but only in a sculptural way. Organic and artistic forms lend themselves well to modeling. Surface modeling is available in Rapidform, Geomagic, Rhino 3D, Maya, T Splines. 
This nuance determines the sequence and method of creating a CAD model, so the engineer, taking into account these features, will develop bolts tied not to the outer diameter, but, on the contrary, to the center. Thus, to create such a CAD model, you need to correlate the shape of the object with the design intent. 
Their peculiarity is that the areas on which air is displayed, or bones with a high density are made transparent, and the sections are superimposed in a free alignment interval. The outer ring of biomaterial surrounding the brain is made up of the soft tissues of the skin and muscles on the outside of the skull. All sections are made on a black background. Since they are simple 2D images, when added one-to-one when viewed, the borders of each slice disappear due to their zero thickness. Each DICOM image is a slice about 5 mm thick.
Several models can be made from different thresholds, allowing different colors to represent a specific part of an object. Volumetric rendering is most often used to render a scanned object. 
Gradually, they replace the outdated gypsum technology. CAD/CAM software is used to create prostheses and implants.
Many dentistry uses CAD/CAM as well as 3D scanners to capture the 3D surface of a dentifrice (in vivo or in vitro) in order to create a digital model using CAD or CAM techniques (e.g. , for a CNC milling machine (computer numerical control), as well as a 3D printer). Such systems are designed to facilitate the process of 3D scanning of the drug in vivo with its further modeling (for example, for a crown, filling or inlay). 
The problem is that the same degree of automation is required for quality assurance. A striking example is the automated assembly of modern cars, because they consist of many parts that must match exactly with each other.
Optimum performance levels are guaranteed by quality assurance systems. Geometrical metal parts need special checking, because they must be of the correct size, fit together to ensure reliable operation.
In highly automated processes, the results of geometric measurements are transferred to machines that produce the corresponding objects. Due to friction and other mechanical processes, the digital model may differ slightly from the real object. In order to automatically capture and evaluate these deviations, the manufactured parts must be rescanned. For this, 3D scanners are used, which create a reference model with which the received data are compared.
The process of comparing 3D data and a CAD model is called CAD comparison and can be a useful method for determining mold and machine wear levels, final assembly accuracy, gap analysis, and the volumetric surface of a disassembled part.
