Views: 0 Author: Site Editor Publish Time: 2022-11-25 Origin: Site
Handheld laser scanners create 3D images through the triangulation mechanism described above: laser points or lines are projected onto the object from the handheld device, and sensors (usually charge-coupled devices or position-sensitive devices) measure the distance to the surface.Data is collected relative to the internal coordinate system,so to collect data where the scanner is moving,the position of the scanner must be determined.This position can be determined by the scanner using reference features on the scanned surface (usually adhesive reflective labels,or by using external tracking methods.External tracking typically takes the form of a laser tracker (providing sensor position) and integrated cameras (orienting the scanner),or a photogrammetric solution using 3 or more cameras to provide the scanner's complete six degrees of freedom.Both technologies tend to use infrared light-emitting diodes attached to the scanner,which are seen by the camera through a filter, providing flexibility to ambient lighting.Data is collected and recorded by a computer as data points in three-dimensional space,which can be processed to convert it into a triangulated mesh and then a computer-aided design model,usually a non-uniform rational B-spline surface.Handheld laser scanners can combine this data with passive visible light sensors (capturing surface texture and color) to build (or "reverse engineer") a complete 3D model.
A structured light 3D scanner projects a pattern of light onto an object and observes how the pattern deforms on the object.Use an LCD projector or other steady light source to project the pattern onto the subject.The camera is slightly offset from the pattern projector,observes the shape of the pattern and calculates the distance of each point in the field of view.Structured light scanning remains a very active area, which can solve correspondence problems and allow error detection and error correction.The advantages of structured light 3D scanners are speed and precision.Instead of scanning one point at a time, a structured light scanner scans multiple points or the entire field of view at a time.Scanning the entire field of view in fractions of a second reduces or eliminates motion-induced distortion problems.Some existing systems are capable of scanning moving objects in real time.Developed a real-time scanner using digital fringe projection and phase-shifting techniques (certain structured light methods) to capture, reconstruct and render high-density details of dynamically deformable objects such as facial expressions at 40 frames per second.Recently,another scanner was developed. The system can apply different modes,and the frame rate of acquisition and data processing reaches 120 frames per second.It can also scan isolated surfaces,such as two moving hands. used binary defocusing technology to achieve a speed breakthrough of hundreds of to thousands of frames per second.
Modulated light
Modulated light 3D scanners emit constantly changing light at objects.Typically, a light source simply cycles its amplitude in a sinusoidal pattern.The camera detects the reflected light,and the amount the pattern moves determines how far the light travels.Modulating light also allows the scanner to ignore light from sources other than lasers, so there is no interference.
Volumetric techniques
Computed tomography (CT) is a medical imaging method that produces a three-dimensional image of the interior of an object from a large number of two-dimensional x-ray images,similarly magnetic resonance imaging is another medical imaging technique that provides greater contrast than computed tomography (CT) is better able to scan between the different soft tissues of the body,making it particularly useful in neuro (brain),musculoskeletal, cardiovascular and oncological (cancer) imaging.These techniques produce discrete 3D volumetric representations that can be directly visualized, manipulated, or converted to traditional 3D surfaces via isosurface extraction algorithms.
Industrial
Computed tomography (CT) is a medical imaging method that produces a three-dimensional image of the interior of an object from a large number of two-dimensional x-ray images, similarly magnetic resonance imaging is another medical imaging technique that provides better contrast than computer Tomography (CT) is able to better scan the different soft tissues of the body,making it particularly useful in neuro (brain),musculoskeletal,cardiovascular and oncological (cancer) imaging.These techniques produce discrete 3D volumetric representations that can be directly visualized, manipulated, or converted to traditional 3D surfaces via isosurface extraction algorithms.
Non-contact passive
Passive 3D imaging solutions do not emit any type of radiation themselves,but instead rely on detecting reflected ambient radiation.Most of these solutions detect visible light since it is a readily available ambient radiation. Other types of radiation can also be used, such as infrared.Passive methods can be very cheap as in most cases they require no specific hardware other than a simple digital camera.
Stereoscopic systems typically use two slightly separated cameras to view the same scene.By analyzing the subtle differences between the images seen by each camera,the distance of each point in the image can be determined.This approach is based on the same principles that drive stereo vision in humans.
Photometric systems typically use a single camera,but take multiple images under different lighting conditions.These techniques attempt to invert the image formation model to recover the surface orientation of each pixel.
Contour technique uses a series of photographs to create a silhouette around a three-dimensional object against a contrasting background.These outlines are extruded and intersected to form an approximation of the object's visual shell.Some concave surfaces of objects (like the inside of a bowl) cannot be detected using these methods.
Space experiments,the European Space Agency has used 3D scanning technology to scan space rocks.
Construction and civil engineering.
Robot control: Laser scanners, for example, can act as the "eyes" of a robot.
As-built drawings of bridges, industrial plants and monuments.
Historic sites.
Site modeling and layout.
Quality Control.
Quantitative survey.
Payload monitoring.
Highway redesign.
Establish a baseline of pre-existing shape/state to detect structural changes due to exposure to extreme loads such as earthquakes,ship/truck impacts, or fire.
Creation of GIS (Geographic Information System) maps and geographic information.
Subsurface laser scanning in mines and karst voids.
Forensic documents.
Design process
Increased accuracy in handling complex parts and shapes.
Coordinate product designs using parts from multiple sources.
Update old CD scans with newer technology.
Replacement of missing or worn parts.
Savings by allowing design-as-built services, for example in car factories.
"Bring the Factory to Engineers" via network share scan, and Save money on travel.
Entertainment
The entertainment industry uses 3D scanners to create digital 3D models for movies,video games,and leisure purposes.They are heavily used in virtual cinematography.Scanning a real-world object is much faster than manually creating a model using 3D modeling software,where an equivalent model exists in the real world.Often,artists sculpt a physical model of what they want and scan it into digital form,rather than creating a digital model directly on the computer.
3D photography
3D scanners are being developed to represent 3D objects in an accurate manner using cameras.Since 2010,companies that create 3D portraits of people (either 3D figurines or 3D selfies) have emerged.
Law enforcement.
Law enforcement agencies around the world are using 3D laser scanning. 3D models are used for field documentation of:
Crime scene.
Bullet trajectory.
Bloodstain pattern analysis.
Incident reconstruction.
Bombings.
Plane crash etc.
Reverse engineering
Reverse engineering of mechanical components requires an accurate digital model of the object to be reproduced.Rather than a set of points,an accurate digital model can be represented by a polygonal mesh, a set of flat or curved NURBS surfaces,or an idealized CAD solid model of a mechanical component. 3D scanners can be used to digitize free-form or gradient-shaped components as well as prismatic geometries,whereas coordinate measuring machines are typically only used to determine simple dimensions of highly prismatic models.These data points are then processed to create a usable digital model,often using specialized reverse engineering software etc.
