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A fiducial marker or fiducial is an object placed in the field of view of an image for use as a point of reference or a measure. It may be either something placed into or on the imaging subject, or a mark or set of marks in the reticle of an optical instrument.
In high-resolution optical microscopy, fiducials can be used to actively stabilize the field of view. Stabilization to better than 0.1 nm is achievable. [1]
In physics, 3D computer graphics, and photography, fiducials are reference points: fixed points or lines within a scene to which other objects can be related or against which objects can be measured. Cameras outfitted with Réseau plates produce these reference marks (also called Réseau crosses) and are commonly used by NASA. Such marks are closely related to the timing marks used in optical mark recognition.[ citation needed ]
Airborne geophysical surveys also use the term "fiducial" as a sequential reference number in the measurement of various geophysical instruments during a survey flight. This application of the term evolved from air photo frame numbers that were originally used to locate geophysical survey lines in the early days of airborne geophysical surveying. This method of positioning has since been replaced by GPS, but the term "fiducial" continues to be used as the time reference for data measured during flights.[ citation needed ]
In applications of augmented reality, fiducials help resolve several problems of integration between the real world view and the synthetic images that augment it. [2] Fiducials of known pattern and size can serve as real world anchors of location, orientation and scale. They can establish the identity of the scene or objects within the scene. For example, a fiducial printed on one page of an augmented reality popup book would identify the page to allow the system to select the augmentation content. It would also serve to moor the coordinates of the augmented content to the three dimensional location, orientation and scale of the open book, helping to create a stable and accurate fusion of real and synthetic imagery.
A slightly more complex example would be multiple fiducials, each attached to an individual piece in an augmented reality board game.
The appearance of markers in images may act as a reference for image scaling, or may allow the image and physical object, or multiple independent images, to be correlated. By placing fiducial markers at known locations in a subject, the relative scale in the produced image may be determined by comparison of the locations of the markers in the image and subject. In applications such as photogrammetry, the fiducial marks of a surveying camera may be set so that they define the principal point, in a process called "collimation".[ citation needed ] This would be a creative use of how the term collimation is conventionally understood.
Some barcode readers can estimate the translation, orientation, and vertical depth of a known-size barcode relative to the barcode reader. [3]
Some sets of fiducial markers are specifically designed to allow rapid, low-latency detection of 6D position estimation (3D location and 3D orientation) and identity of hundreds of unique fiducial markers. [4] For example, the ArUco markers, [5] the WhyCon marker, [6] WhyCode markers, [4] "amoeba" reacTIVision fiducials, the d-touch fiducials, [7] [8] [9] or the TRIP circular barcode tags (ringcodes). [10]
Fiducial markers are used in a wide range of medical imaging applications. Images of the same subject produced with two different imaging systems may be correlated by placing a fiducial marker in the area imaged by both systems. In this case, a marker which is visible in the images produced by both imaging modalities must be used. By this method, functional information from SPECT or positron emission tomography can be related to anatomical information provided by magnetic resonance imaging (MRI). [11]
Similarly, fiducial points established during MRI can be correlated with brain images generated by magnetoencephalography to localize the source of brain activity. Such fiducial points or markers are often created in tomographic images such as computed tomography, magnetic resonance and positron emission tomography images using devices such as the N-localizer [12] and Sturm-Pastyr localizer. [13]
In electrocardiography (ECG), fiducial points are landmarks on the ECG complex such as the isoelectric line (PQ junction), and onset of individual waves such as PQRST.
In processes that involve following a labelled molecule as it is incorporated in some larger polymer, such markers can be used to follow the dynamics of growth/shrinkage of the polymer, as well as its movement. Commonly used fiducial markers are fluorescently labelled monomers of bio-polymers. The task of measuring and quantifying what happens to these is borrowed from methods in physics and computational imaging like speckle imaging.
Automated behavioural tracking systems are used to study the organisation of social insect colonies, and the behaviour of individual colony members. These systems combine fiducial markers and machine vision to output the location and orientation of colony members multiple times per second and have, among other insights, revealed the social network structure of ant Camponotus fellah . [14]
In radiotherapy and radiosurgical systems, fiducial points are landmarks in the tumour to facilitate correct targets for treatment. In neuronavigation, a "fiducial spatial coordinate system" is used as a reference, for use in neurosurgery, to describe the position of specific structures within the head or elsewhere in the body. Such fiducial points or landmarks are often created in magnetic resonance imaging and computed tomography images by using the N-localizer or Sturm-Pastyr localizer.
In printed circuit board (PCB) manufacturing, fiducial marks, also known as circuit pattern recognition marks, allow SMT placement equipment to accurately locate and place parts on boards. These devices locate the circuit pattern by providing common measurable points. They are usually made by leaving a circular area of the board bare from solder-mask coating. Inside this area is a circle exposing the copper plating beneath. This center metallic disc can be solder-coated, gold-plated or otherwise treated, although bare copper is most common if not a current-carrying contact. Alternatively, it is possible to use clear solder-mask lacquer to cover the fiducials. In order to minimize rounding errors it was good practice to place fiducials in the same grid (or some multiple of it) that was used to place the parts, however, this isn't always possible on high-density boards nor is it a requirement any more with modern high-precision machines.
Most placement machines are fed boards for assembly by a rail conveyor, with the board being clamped down in the assembly area of the machine. Each board will clamp slightly differently than the others, and the variance—which will generally be only tenths of a millimeter—is sufficient to ruin a board without proper calibration. Consequently, a typical PCB will have multiple fiducials to allow placement robots to precisely determine the board's orientation. By measuring the location of the fiducials relative to the board plan stored in the machine's memory, the machine can reliably compute the degree to which parts must be moved relative to the plan, called offset, to ensure accurate placement.
Using three fiducials enables the machine to determine PCB offset in both the X and Y axes, as well as to determine if the board has rotated during clamping, allowing the machine to rotate parts to be placed to match. Such fiducials are also called global fiducials. Global fiducials are also used in conjunction with stencil printing. Without them the printer would not print the solder paste in exact alignment with the pads. Parts requiring a very high degree of placement precision, such as ball grid array packages, may have additional local fiducials near the package placement area of the board to further fine-tune the targeting. Local fiducial, however, cannot be used in the stencil printing process.
Conversely, low end, low-precision boards may only have two fiducials, or use fiducials applied as part of the screen printing process applied to most circuit boards. Some very low-end boards may use the plated mounting screw holes as fiducials, although this yields very low accuracy.
For prototyping and small batch production runs, the use of a fiducial camera can greatly improve the process of board fabrication. By automatically locating fiducial markers, the camera automates board alignment. This helps with front to back and multilayer applications, eliminating the need for set pins. [15]
In color printing, fiducials—also called "registration black"—are used at the edge of the cyan, magenta, yellow and black (CMYK) printing plates so that they can be correctly aligned with each other.
"Banana for scale" refers to an Internet meme involving using a banana as a fiducial marker. The meme began in August 2010, where a man posted to Facebook a picture of a safe with a banana beside it. From there, the meme spread primarily via Reddit; The Daily Dot remarked that "[the meme] had become a hilarious game with redditors try to one up each other. It's a trend in the same vein as planking." [16]
A printed circuit board (PCB), also called printed wiring board (PWB), is a medium used to connect or "wire" components to one another in a circuit. It takes the form of a laminated sandwich structure of conductive and insulating layers: each of the conductive layers is designed with a pattern of traces, planes and other features etched from one or more sheet layers of copper laminated onto or between sheet layers of a non-conductive substrate. Electrical components may be fixed to conductive pads on the outer layers, generally by means of soldering, which both electrically connects and mechanically fastens the components to the board. Another manufacturing process adds vias, drilled holes that allow electrical interconnections between conductive layers.
Augmented reality (AR) is an interactive experience that combines the real world and computer-generated 3D content. The content can span multiple sensory modalities, including visual, auditory, haptic, somatosensory and olfactory. AR can be defined as a system that incorporates three basic features: a combination of real and virtual worlds, real-time interaction, and accurate 3D registration of virtual and real objects. The overlaid sensory information can be constructive, or destructive. As such, it is one of the key technologies in the reality-virtuality continuum.
Surface-mount technology (SMT), originally called planar mounting, is a method in which the electrical components are mounted directly onto the surface of a printed circuit board (PCB). An electrical component mounted in this manner is referred to as a surface-mount device (SMD). In industry, this approach has largely replaced the through-hole technology construction method of fitting components, in large part because SMT allows for increased manufacturing automation which reduces cost and improves quality. It also allows for more components to fit on a given area of substrate. Both technologies can be used on the same board, with the through-hole technology often used for components not suitable for surface mounting such as large transformers and heat-sinked power semiconductors.
The scale-invariant feature transform (SIFT) is a computer vision algorithm to detect, describe, and match local features in images, invented by David Lowe in 1999. Applications include object recognition, robotic mapping and navigation, image stitching, 3D modeling, gesture recognition, video tracking, individual identification of wildlife and match moving.
Image-guided surgery (IGS) is any surgical procedure where the surgeon uses tracked surgical instruments in conjunction with preoperative or intraoperative images in order to directly or indirectly guide the procedure. Image guided surgery systems use cameras, ultrasonic, electromagnetic or a combination of fields to capture and relay the patient's anatomy and the surgeon's precise movements in relation to the patient, to computer monitors in the operating room or to augmented reality headsets. This is generally performed in real-time though there may be delays of seconds or minutes depending on the modality and application.
Surface-mount technology (SMT) component placement systems, commonly called pick-and-place machines or P&Ps, are robotic machines which are used to place surface-mount devices (SMDs) onto a printed circuit board (PCB). They are used for high speed, high precision placing of a broad range of electronic components onto the PCBs which are in turn used in computers, consumer electronics, and industrial, medical, automotive, military and telecommunications equipment. Similar equipment exists for through-hole components. This type of equipment is sometimes used to package microchips using the flip chip method.
Image-guided radiation therapy is the process of frequent imaging, during a course of radiation treatment, used to direct the treatment, position the patient, and compare to the pre-therapy imaging from the treatment plan. Immediately prior to, or during, a treatment fraction, the patient is localized in the treatment room in the same position as planned from the reference imaging dataset. An example of IGRT would include comparison of a cone beam computed tomography (CBCT) dataset, acquired on the treatment machine, with the computed tomography (CT) dataset from planning. IGRT would also include matching planar kilovoltage (kV) radiographs or megavoltage (MV) images with digital reconstructed radiographs (DRRs) from the planning CT.
Neuronavigation is the set of computer-assisted technologies used by neurosurgeons to guide or "navigate" within the confines of the skull or vertebral column during surgery, and used by psychiatrists to accurately target rTMS. The set of hardware for these purposes is referred to as a neuronavigator.
Virtual graffiti consists of virtual or digital media applied to public locations, landmarks or surfaces. Virtual graffiti applications utilize augmented reality and ubiquitous computing to anchor virtual graffiti to physical landmarks or objects in the real world. The virtual content can then be viewed through digital devices. Virtual graffiti is aimed at delivering messaging and social multimedia content to mobile applications and devices based on the identity, location, and community of the user.
The 5DX was an automated X-ray inspection robot, which belonged to the set of automated test equipment robots and industrial robots utilizing machine vision. The 5DX was manufactured by Hewlett Packard, then later Agilent Technologies when HP was split into Hewlett Packard and Agilent Technologies in 1999. The 5DX performed a non-destructive structural test using X-ray laminography (tomography) to take 3D images of an assembled printed circuit board using 8-bit grayscale to indicate solder thickness. It was used in the assembled printed circuit board (PCB) electronics manufacturing industry to provide process feedback to a surface mount technology assembly line, as well as defect capture.
Positron emission tomography–computed tomography is a nuclear medicine technique which combines, in a single gantry, a positron emission tomography (PET) scanner and an x-ray computed tomography (CT) scanner, to acquire sequential images from both devices in the same session, which are combined into a single superposed (co-registered) image. Thus, functional imaging obtained by PET, which depicts the spatial distribution of metabolic or biochemical activity in the body can be more precisely aligned or correlated with anatomic imaging obtained by CT scanning. Two- and three-dimensional image reconstruction may be rendered as a function of a common software and control system.
CyberCode is a visual tagging system based on a 2D barcode technology. Designed to be read by low-cost CMOS or CCD cameras common in mobile devices, it can also be used to determine the 3D position of the tagged object as well as its ID number.
Viscom AG is a manufacturer of inspection technologies, in particular for automatic optical inspection (AOI) and X-ray inspection, with headquarters in Hanover, Germany, used in automotive electronics, entertainment electronics, telecommunications and industrial electronics.
Cone beam computed tomography is a medical imaging technique consisting of X-ray computed tomography where the X-rays are divergent, forming a cone.
Vuforia is an augmented reality software development kit (SDK) for mobile devices that enables the creation of augmented reality applications. It uses computer vision technology to recognize and track planar images and 3D objects in real time. This image registration capability enables developers to position and orient virtual objects, such as 3D models and other media, in relation to real world objects when they are viewed through the camera of a mobile device. The virtual object then tracks the position and orientation of the image in real-time so that the viewer's perspective on the object corresponds with the perspective on the target. It thus appears that the virtual object is a part of the real-world scene.
An ARTag is a fiducial marker system to support 3D registration (alignment) and pose tracking in augmented reality. They can be used to facilitate the appearance of virtual objects, games, and animations within the real world. Like the earlier ARToolKit system, they allow for video tracking capabilities that calculate a camera's position and orientation relative to physical markers in real time. Once the camera's position is known, a virtual camera can be positioned at the same point, revealing the virtual object at the location of the ARTag. It thus addresses two of the key problems in Augmented Reality: viewpoint tracking and virtual object interaction.
The N-localizer is a device that enables guidance of stereotactic surgery or radiosurgery using tomographic images that are obtained via computed tomography (CT), magnetic resonance imaging (MRI), or positron emission tomography (PET). The N-localizer comprises a diagonal rod that spans two vertical rods to form an N-shape and permits calculation of the point where a tomographic image plane intersects the diagonal rod. Attaching three N-localizers to a stereotactic instrument allows calculation of three points where a tomographic image plane intersects three diagonal rods. These points determine the spatial orientation of the tomographic image plane relative to the stereotactic frame.
The Augmented Reality Markup Language (ARML) is a data standard to describe and interact with augmented reality (AR) scenes. It has been developed within the Open Geospatial Consortium (OGC) by a dedicated ARML 2.0 Standards Working Group. ARML consists of both an XML grammar to describe the location and appearance of virtual objects in the scene, as well as ECMAScript bindings to allow dynamic access to the properties of the virtual objects, as well as event handling, and is currently published in version 2.0. ARML focuses on visual augmented reality.
Component placement is an electronics manufacturing process that places electrical components precisely on printed circuit boards (PCBs) to create electrical interconnections between functional components and the interconnecting circuitry in the PCBs (leads-pads). The component leads must be accurately immersed in the solder paste previously deposited on the PCB pads. The next step after component placement is soldering.
Stencil printing is the process of depositing solder paste on the printed wiring boards (PWBs) to establish electrical connections. It is immediately followed by the component placement stage. The equipment and materials used in this stage are a stencil, solder paste, and a printer.
