Fiduciary marker
Encyclopedia
A fiducial marker or fiducial is an object used in the field of view
of an imaging system which appears in the image produced, 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.
, 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 reseau plate
s produce these reference marks (also called reseau crosses) and are commonly used by NASA
. Such marks are closely related to the timing mark
s used in optical mark recognition
.
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 This method of positioning has since been replaced by GPS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.
Markers may be used to make otherwise invisible or difficult to distinguish features of an image more visible. Markers can simplify computerized image processing
applications such as motion capture
, by providing an easy-to-track feature in images which follows the movements of the marked subject.
or virtual reality
, fiducials are often manually applied to objects in a scene so that the objects can be recognized in images of the scene. For example, to track some object, a light-emitting diode
can be applied to it. With knowledge of the color of the emitted light, the object can easily be identified in the picture.
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 fiduciary 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
". This would be a creative use of how the term collimation is conventionally understood.
applications. Images of the same subject produced with two different imaging systems may be correlated by placing a fiduciary 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). Similarly, fiducial points established during MRI can be correlated with brain images generated by magnetoencephalography to localize the source of brain activity.
.
, 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.
(PCB) design, fiducial marks, also known as circuit pattern recognition marks or simply "fids," allow automated assembly 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-stop coating (similar to clearcoat), in which a filled copper circle is placed. This center metallic disc can be solder-coated, gold-plated or otherwise treated, although bare copper is most common as it is not a current-carrying contact.
Most placement devices 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 three fids to allow placement robots to precisely determine the board's orientation. By measuring the location of the fids 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 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. Parts requiring a very high degree of placement precision, such as integrated circuit
chip packages with many fine leads, may have subsidiary fiducial marks near the package placement area of the board to further fine-tune the targeting.
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 ersatz fiducials, although this yields very low accuracy.
, 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.
Field of view
The field of view is the extent of the observable world that is seen at any given moment....
of an imaging system which appears in the image produced, 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.
Accuracy
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 (Carter et al. Applied Optics, (2007)).Physics
In physicsPhysics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
, 3D computer graphics
3D computer graphics
3D computer graphics are graphics that use a three-dimensional representation of geometric data that is stored in the computer for the purposes of performing calculations and rendering 2D images...
, and photography
Photography
Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...
, 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 reseau plate
Reseau plate
A Reseau plate is a transparent plate with fiduciary markers placed at the focal plane of a camera just in front of the film to provide a means of correcting images to enable them to be used for precision measurement...
s produce these reference marks (also called reseau crosses) and are commonly used by NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
. Such marks are closely related to the timing mark
Timing mark
A timing mark is an indicator used for setting the timing of the ignition system of an engine, typically found on the crankshaft pulley or the flywheel, being the largest radius rotating at crankshaft speed and therefore the place where marks at one degree intervals will be farthest apart.On older...
s used in optical mark recognition
Optical mark recognition
Optical Mark Recognition is the process of capturing human-marked data from document forms such as surveys and tests.-OMR background:...
.
Geographical Survey
Airborne geophysicalGeophysics
Geophysics is the physics of the Earth and its environment in space; also the study of the Earth using quantitative physical methods. The term geophysics sometimes refers only to the geological applications: Earth's shape; its gravitational and magnetic fields; its internal structure and...
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
Aerial photography
Aerial photography is the taking of photographs of the ground from an elevated position. The term usually refers to images in which the camera is not supported by a ground-based structure. Cameras may be hand held or mounted, and photographs may be taken by a photographer, triggered remotely or...
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
Global Positioning System
The Global Positioning System is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...
, but the term "fiducial" continues to be used as the time reference for data measured during flights.
Markers may be used to make otherwise invisible or difficult to distinguish features of an image more visible. Markers can simplify computerized image processing
Image processing
In electrical engineering and computer science, image processing is any form of signal processing for which the input is an image, such as a photograph or video frame; the output of image processing may be either an image or, a set of characteristics or parameters related to the image...
applications such as motion capture
Motion capture
Motion capture, motion tracking, or mocap are terms used to describe the process of recording movement and translating that movement on to a digital model. It is used in military, entertainment, sports, and medical applications, and for validation of computer vision and robotics...
, by providing an easy-to-track feature in images which follows the movements of the marked subject.
Virtual Reality
In applications of augmented realityAugmented reality
Augmented reality is a live, direct or indirect, view of a physical, real-world environment whose elements are augmented by computer-generated sensory input such as sound, video, graphics or GPS data. It is related to a more general concept called mediated reality, in which a view of reality is...
or virtual reality
Virtual reality
Virtual reality , also known as virtuality, is a term that applies to computer-simulated environments that can simulate physical presence in places in the real world, as well as in imaginary worlds...
, fiducials are often manually applied to objects in a scene so that the objects can be recognized in images of the scene. For example, to track some object, a light-emitting diode
Diode
In electronics, a diode is a type of two-terminal electronic component with a nonlinear current–voltage characteristic. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material connected to two electrical terminals...
can be applied to it. With knowledge of the color of the emitted light, the object can easily be identified in the picture.
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 fiduciary 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
Photogrammetry
Photogrammetry is the practice of determining the geometric properties of objects from photographic images. Photogrammetry is as old as modern photography and can be dated to the mid-nineteenth century....
, the fiducial marks of a surveying camera may be set so that they define the principal point, in a process called "collimation
Collimator
A collimator is a device that narrows a beam of particles or waves. To "narrow" can mean either to cause the directions of motion to become more aligned in a specific direction or to cause the spatial cross section of the beam to become smaller.- Optical collimators :In optics, a collimator may...
". This would be a creative use of how the term collimation is conventionally understood.
Medical Imaging
Fiduciary markers are used in a wide range of medical imagingMedical imaging
Medical imaging is the technique and process used to create images of the human body for clinical purposes or medical science...
applications. Images of the same subject produced with two different imaging systems may be correlated by placing a fiduciary 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
Positron emission tomography
Positron emission tomography is nuclear medicine imaging technique that produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide , which is introduced into the body on a...
can be related to anatomical information provided by magnetic resonance imaging
Magnetic resonance imaging
Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...
(MRI). Similarly, fiducial points established during MRI can be correlated with brain images generated by magnetoencephalography to localize the source of brain activity.
ECG
In electrocardiography, fiducial points are landmarks on the ECG complex such as the isoelectric line (PQ junction), and onset of individual waves such as PQRST.Cell Biology
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 fiduciary 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 imagingSpeckle imaging
Speckle imaging describes a range of high-resolution astronomical imaging techniques based either on the shift-and-add method or on speckle interferometry methods...
.
Radio Therapy
In radiotherapy and radiosurgical systems such as the CyberKnife, fiducial points are landmarks in the tumour to facilitate correct targets for treatment. In neuronavigationNeuronavigation
The term neuronavigation is a neologism used to describe the set of computer-assisted technologies used by neurosurgeons to guide or "navigate” within the confines of the skull or vertebral column during surgery...
, 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.
PCB
In printed circuit boardPrinted circuit board
A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...
(PCB) design, fiducial marks, also known as circuit pattern recognition marks or simply "fids," allow automated assembly 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-stop coating (similar to clearcoat), in which a filled copper circle is placed. This center metallic disc can be solder-coated, gold-plated or otherwise treated, although bare copper is most common as it is not a current-carrying contact.
Most placement devices 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 three fids to allow placement robots to precisely determine the board's orientation. By measuring the location of the fids 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 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. Parts requiring a very high degree of placement precision, such as integrated circuit
Integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
chip packages with many fine leads, may have subsidiary fiducial marks near the package placement area of the board to further fine-tune the targeting.
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 ersatz fiducials, although this yields very low accuracy.
Printing
In color printingColor printing
Color printing or Colour printing is the reproduction of an image or text in color...
, fiducials—also called "registration black
Registration black
In CMYK printing, registration black refers to 100% coverage in each of the four process colors: cyan , magenta , yellow , and black...
"—are used at the edge of the cyan, magenta, yellow and black (CMYK
CMYK color model
The CMYK color model is a subtractive color model, used in color printing, and is also used to describe the printing process itself. CMYK refers to the four inks used in some color printing: cyan, magenta, yellow, and key...
) printing plates so that they can be correctly aligned with each other.