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Topic: Trifocal

	TriFocal Communications
		TriFocal Communications provides innovative marketing and dynamic physician and patient education materials to the healthcare industry.
		Our team offers a skilled network of professionals in a variety of areas from marketing, project management, medical writing and illustration, who are dedicated to developing strategies and concepts that guide pharmaceutical and healthcare products to the forefront of their marketplace.
		The success of our company has been built on our ability to bring added value to marketing tools, that heighten physician's reception of current sales and educational messages.
	www.trifocal.net (85 words)

	PublicationsChristian Perwass
		A Geometric Derivation of the Trifocal Tensor and its Constraints
		Furthermore, we will give a novel expression for the trifocal tensor, derive constraints on its geometrical structure and investigate its reconstruction ability computationally.
		This technical report is an extended version of the paper "A Geometric Analysis of the Trifocal Tensor".
	www.perwass.de /cbup/paper5.html (126 words)

	Segmented Eyeglass Lenses Such as Bifocals and Trifocals for Presbyopia - AllAboutVision.com
		Trifocals are lenses with three points of focus: usually for distance, intermediate and near.
		Trifocals have an added segment above the bifocal for viewing things in the intermediate zone, which is farther than the near zone: about arm's length away.
		Trifocals are fitted a bit higher, with the top line of the intermediate area placed even with the pupil.
	www.allaboutvision.com /over40/segmented.htm (815 words)

	The Trifocal Tensor
		The trifocal tensor approach is such an extension and maintains a similar projective geometry spirit.
		For instance, if a point P is in the trifocal plane, the fundamental matrices cannot determine if its 3 images belong to a single 3D point.
		However, the trifocal tensor's 27 scalar parameters are not all independent unknowns.
	www1.cs.columbia.edu /~jebara/htmlpapers/SFM/node9.html (437 words)

	Focal Points Bifocals, Trifocals and Progressive-Addition Lenses
		Trifocals were first introduced in the 1930s, as a modification of the processes for bifocals.
		Trifocal lenses were the initial attempt to solve this problem, by providing three different powers for distance, intermediate, and near vision.
		Although several other types of trifocals are available, most are flat-top or Executive-style segments (see Figure 1e), in which the distance portion remains the same and the segment is divided for the intermediate add.
	www.eyemdny.com /Dr__Wisnicki_-_CV/Publications/Focal_Points/body_focal_points.html (3720 words)

	Trifocal Information
		Trifocals are eyeglasses where the lenses have 3 regions to correct for distance, intermediate (arm's length), and near vision.
		Trifocal lenses are made in similar styles to bifocals, but with an additional segment for intermediate vision above the reading section.
		Trifocals are becoming rarer as more people choose to wear progressive lenses.
	www.bookrags.com /wiki/Trifocal (165 words)

	Trifocal - Wikipedia, the free encyclopedia
		Trifocals are eyeglasses where the lenses have 3 regions to correct for distance, intermediate (arm's length), and near vision.
		Trifocal lenses are made in similar styles to bifocals, but with an additional segment for intermediate vision above the reading section.
		Trifocals are becoming rarer as more people choose to wear progressive lenses.
	en.wikipedia.org /wiki/Trifocal (188 words)

	Magnifics Inc - Cellular phone accessories magnifying cell phone displays for easier viewing and for the visually ...
		trifocal means that there are three different lens powers incorporated into an eyeglass lens, each providing a different zone of focus.
		In a trifocal, a third lens power is inserted directly above the bifocal segment, which is designed to be in focus for the intermediate distance of 18 to 26 inches.
		You should consider trifocals if you continually have difficulty seeing or performing visual tasks in the range of 18 to 26 inches.
	www.thephonemonocle.com /medical/Trifocals.htm (453 words)

	Institute of Photogrammery and Remote Sensing - TU Vienna
		After determining the trifocal tensor, the basis vectors and rotation matrices of the relative orientation of the three images can be extracted easily if the interior orientation of the images is known.
		The determination of a valid trifocal tensor in the Gauß-Helmert model can be done basically in two ways: By parameterizing the tensor using its 27 elements and introducing the 8 internal constraints together with the scale fixing, or by using an alternative parameterization for the trifocal tensor that has 18 degrees of freedom.
		For computing a valid trifocal tensor by minimizing reprojection error in the Gauß-Helmert model it is important to have a consistent representation for the trifocal tensor.
	www.ipf.tuwien.ac.at /teaching/geow_mitt_kurzf/gw_car_03_a.html (1102 words)

	Trifocal neuralgia - WrongDiagnosis.com
		Trifocal neuralgia (medical condition): Facial pain associated with the trigeminal nerve.
		Trifocal neuralgia: Another name for Trigeminal neuralgia (or close medical condition association).
		Trigeminal neuralgia, also called tic douloureux, is a condition that affects the trigeminal nerve (the 5th cranial nerve), one of the largest nerves in the head.
	www.wrongdiagnosis.com /medical/trifocal_neuralgia.htm (469 words)

	Sutherlin Optical Lab (Site not responding. Last check: )
		The distance optical center of a standard bifocal, or trifocal lens is the thinnest part of a minus lens and the thickest part of a plus lens.
		Segment centers cannot be spotted on a lensometer for bifocals, or trifocals unless the distance power of the lens is Plano, or 0.00.
		The first number in a trifocal gives the height measured from the top of the bifocal part of the segment to the top of the trifocal portion.
	www.sutherlinoptical.com /AllAboutLensStyles.asp (761 words)

	Glossary (Site not responding. Last check: )
		The intermediate band is 14 mm high compared to the 7 to 8 mm high intermediate on the conventional trifocal.
		Conventional trifocals are also available with these wider widths, but the typical trifocal uses a 28 mm wide seg.
		When the CRT trifocal is designed correctly, the top most seg line cuts through the middle of the pupil.
	www.eye-doctor.com /glossary.htm (961 words)

	IBMR:docs
		Much like the F-matrix, the trifocal tensor describes the projective relation, but this time between three views.
		It imposes trifocal constraints on the images (something that 3 F-matrices cannot do), and this allows for better recovery of projection matrices as well as eliminating many degenerate cases.
		Fundamental matrices can be extracted for any of the three views, and inversely, tri-tensor can be estimated from three f-matrices that satisfy the trifocal constraint.
	www.ibmr.net /index.php?dest=docs&subdir=TT (167 words)

	Personal Web Page
		The trifocal tensor has been used in many video applications such as image-based rendering, 3D modeling and augmented reality.
		The trifocal tensor of the evolving view triplets is computed at the realtime.
		The goal is to automatically insert into live video a computer generated model of an object that is not physically present in the scene.
	www.site.uottawa.ca /~jiali/research.html (631 words)

	A New Characterization of the Trifocal Tensor - Papadopoulo, Faugeras (ResearchIndex)
		This paper deals with the problem of characterizing and parametrizing the manifold of trifocal tensors that describe the geometry of three views like the fundamental matrix characterizes the geometry of two.
		First a new, simpler, set of algebraic constraints that characterizes the set of trifocal tensors is presented.
		Second, we give a new parametrization of the trifocal tensor based upon those constraints which is also simpler than previously known...
	citeseer.ist.psu.edu /382509.html (646 words)

	Eye Information Network - Your Source For Eye Information on the Net
		Trifocal glasses are the same as bifocals, except that there is an additional power in the middle part of the lens to correct for the computer distance (about 45 to 60 cm).
		These lenses include distance, trifocal, and bifocal powers all blended together with a gradual change from one to the next.
		Trifocal lenses that have visible lines are lenses that contain three powers, distance, computer, and reading.
	www.eye-info-network.com /bifocal/readglasses.asp (766 words)

	Geometry/Structure Estimation Procedure
		The trifocal tensor can be estimated from six or more corresponding points in three views.
		The matching points identified in a sequence are used to get a preliminary estimate of the trifocal tensor, from triples of corresponding vertices in the first, the last and an intermediate image.
		This preliminary estimate is used to refine the correspondences by epipolar line search in the second image and point transfer to the third one via the trifocal tensor.
	www.ien.it /is/rec3d/structure.html (343 words)

	Three view geometry
		This point then projects to a unique point in the third image, as can be seen in Figure 3.7, even when this point is located in the trifocal plane.
		Therefore, one can conclude that in the three view case not all the information is described by the epipolar geometry.
		This transfer is also described by the trifocal tensor.
	www.cs.unc.edu /~marc/tutorial/node45.html (471 words)

	Trifocal Tensor Estimation
		For the case of three given images, all projectively relevant camera parameters are encapsulated in a single mathematical object, the trifocal tensor.
		However, reliable estimation of the trifocal tensor is crucial for 3D reconstruction from uncalibrated cameras.
		The scope of the present master thesis comprises an implementation of the nonlinear method proposed in [3] for trifocal tensor estimation and its comparison with the Gold Standard [2].
	lmb.informatik.uni-freiburg.de /masters/canterakis/can031/index.en.html?1000010000000000 (301 words)

	Lenses
		Trifocal lenses, like bifocal lenses, will have visible lines across the lens, either in a D-shaped segment or across the entire lens.
		The top of the lens is for distance, the middle segment is for arm's length tasks, and the bottom segment is for close-up work.
		Instead of having "steps" in the prescription like a bifocal or a trifocal, the change in prescription acts like a "ramp" for a smooth transition from distance, to intermediate, to near viewing.
	www.drburley.com /lenses.htm (440 words)

	[No title] (Site not responding. Last check: )
		This paper investigates the trifocal tensor for an affine trinocular rig and defines an affine trifocal tensor.
		The question of the degrees of freedom of the tensor entries will be addressed, and a novel algorithm to compute the tensor by a linear technique is presented.
		An analysis of the error in the approximation of a generic trifocal tensor by the affine trifocal tensor is carried out and preliminary experiments with synthetic and real data show the reliability and robustness of the approximation under a wide range of conditions.
	www.lycos.com /info/tensor--imaging.html?page=4 (486 words)

	Eye Information Network - Your Source For Eye Information on the Net
		Trifocal glasses are the same as bifocals, except that there is an additional power in the middle part of the lens to correct for the computer distance (about 45 to 60 cm).
		These lenses include distance, trifocal, and bifocal powers all blended together with a gradual change from one to the next.
		Trifocal lenses that have visible lines are lenses that contain three powers, distance, computer, and reading.
	eye-info-network.com /bifocal/readglasses.asp (766 words)

	TriCenturion (Site not responding. Last check: )
		Progressive lens (V2781) is a multifocal lens that gradually changes in lens power from the top to the bottom of the lens, eliminating the line(s) that would otherwise be seen in a bifocal or trifocal lens.
		When billing claims for deluxe frames, use code V2020 for the cost of standard frames and a second line item using code V2025 for the difference between the charges for the deluxe frames and the standard frames.
		When billing claims for progressive lens, use the appropriate code for the standard bifocal (V2200 - V2299) or trifocal (V2300 - V2399) lens and a second line item using code V2781 for the difference between the charge for the progressive lens and the standard lens.
	www.tricenturion.com /content/dmerc/0602_16_07_refractive_lenses.cfm (2088 words)

	Robust Parametrization and Computation of the Trifocal Tensor
		This paper presents an algorithm for computing a Maximum Likelihood Estimate (MLE) of the trifocal tensor.
		The input to the algorithm is three images of the same scene, and the output is the estimated tensor and corner and line feature matches across the three images that are consistent with this estimate.
		Particular novelties of the algorithm are the computation of a trifocal tensor which enforces the constraints between the tensor elements.
	research.microsoft.com /research/pubs/view.aspx?pubid=417 (116 words)

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