bluuebunny/crossref_metadata_2025 huggingface dataset:
Entropion correction by fornix‐based suture placement: use of the Quickert–Rathbun technique in ten dogs
Authors: Williams David L.
Published: August 2004

The objective of this study was to evaluate fornix‐based suture placement as a method for entropion correction in the dog. Lower eyelid entropion with resultant trichiasis was corrected in 10 dogs using fornix‐based suture placement similar to that employed in the Quickert–Rathbun technique used in man. A double‐ended suture was placed originating at the deepest extent of the fornix and exiting the lid 1–2 mm from the eyelid margin. Degree of correction was assessed visually immediately after surgery and at re‐examination with a follow‐up period of up to 6 months. Fornix‐based suture placement led to immediate eversion of the eyelid in each case and thus amelioration of the trichiasis in all dogs. In two cases eyelid eversion initially appeared over‐corrected and in two cases exposure of conjunctival tissue was evident initially at the palpebral margin. In all cases, however, such complications were transient with long‐term results giving an acceptable apposition between ocular surface and eyelid margin in all adult dogs. In three juvenile dogs on which the technique was used, further surgical treatment was required as the puppies grew. Fornix‐based suture placement is a novel approach to entropion correction in the dog which yields acceptable results in the majority of suitable cases without recourse to incisional surgery.
Phaco chop technique for cataract surgery in the dog
Authors: Warren Christi
Published: August 2004

Phaco chop is a bimanual phacoemulsification technique to remove cataracts. The technique was first presented at the 1993 3rd American–International Congress on Cataract, IOL, and Refractive Surgery in Seattle by Dr Kunihiro Nagahara. He compared the lens with a block of wood and by applying chopping forces parallel to the natural planes of the lens lamellae, as one does in splitting wood, a nucleus can be cleaved with surprisingly little force and time. Dr Nagahara used the phaco tip to impale and high vacuum to hold the nucleus while a second instrument, or chopper, hooked the equator and was pulled centrally, splitting the nucleus along its natural cleavage planes. This was a breakthrough for surgeons who had been utilizing several minutes of phaco energy sculpting grooves and bowls in a lens. Studies have shown that compared with four‐quadrant ‘divide and conquer’, the phaco chop technique uses less phaco time and energy, significantly reducing endothelial cell damage. Other advantages of phaco chop include reduction of zonular and capsular stress because forces are directed toward an opposing instrument and the phaco tip is kept in a central ‘safe zone’ in the middle of the pupil. This technique has also been successfully adapted to the canine phacoemulsification procedure. The larger canine lens requires some modifications, and lenses with hard nuclear and cortical material may not be amenable to this procedure.
Canine retinal surgery
Authors: Vainisi Samuel J. , Wolfer Joe C.
Published: August 2004

Retinal detachment is common in dogs and presents major challenges for the veterinary ophthalmologist. This article reviews recent advances in both technology and technique that have greatly increased the success rate of retinal reattachment surgery. Internal and external techniques for the repair of retinal detachments are discussed, as is the etiopathogenesis of vitreoretinal disease in the dog.
Coronal rhytidectomy in conjunction with deep plane walking sutures, modified Hotz‐Celsus and lateral canthoplasty procedure in a dog with excessive brow droop
Authors: McCallum Patrick , Welser Jennifer
Published: August 2004

This case report describes a unique technique of rhytidectomy in a Bloodhound to repair excessive brow folding and droop complicating underlying entropion. This case posed specific challenges due to the loose fascial plane connective tissue. A large circular area of coronal skin was excised, followed by placement of deep plane walking fixation sutures for cosmetic realignment and to alleviate brow droop. In addition, a modified Hotz‐Celsus procedure and lateral canthoplasty were performed to address the primary entropion. The coronal rhytidectomy was considered a successful approach to repair excessive brow droop in this Bloodhound.
The use of porcine small intestinal submucosa for the repair of full‐thickness corneal defects in dogs, cats and horses
Authors: Bussieres Martin , Krohne Sheryl G. , Stiles Jean , Townsend Wendy M.
Published: August 2004

Abstract Objective  To evaluate the efficacy of using a porcine small intestinal submucosa (SIS) graft covered by a conjunctival flap for the surgical repair of full‐thickness corneal wounds in dogs, cats and horses.

Procedure  All records dating from August 1999 to February 2003 from Purdue University Veterinary Teaching Hospital of patients that had undergone ophthalmic surgical procedures and received a SIS corneal graft for a full‐thickness lesion were reviewed. Fifteen cases were identified including six dogs, two cats and seven horses. Requirements for inclusion in this study were that SIS was used as a corneal graft in a full‐thickness corneal defect and that the graft was completely covered with a conjunctival flap.

Results  Of the 15 cases, one canine patient had received SIS following removal of an epibulbar melanocytoma. The remaining five canine patients had undergone this surgical procedure for the repair of corneal perforation. The two feline patients had been presented for corneal perforation following chronic ulceration. One equine patient had been presented for a deep melting ulcer, three for stromal corneal abscesses, and three for corneal perforations. Complications encountered postoperatively included aqueous leakage, conjunctival flap dehiscence, synechia, cataract and fibrin in the anterior chamber. Fourteen out of 15 patients were visual at the final re‐evaluation.

Conclusion  SIS is an inexpensive, easy‐to‐handle biomaterial that appears to be suitable for the repair of full‐thickness corneal wounds in dogs, cats and horses. Results of our study support the conclusion that this relatively new product is an effective alternative to traditional implantation materials utilized in veterinary ophthalmology.
Immature cortical responses to auditory stimuli in specific language impairment: evidence from ERPs to rapid tone sequences
Authors: Bishop D.V.M. , McArthur G.M.
Published: August 2004

Event‐related potentials (ERPs) to tone pairs and single tones were measured for 16 participants with specific language impairment (SLI) and 16 age‐matched controls aged from 10 to 19 years. The tone pairs were separated by an inter‐stimulus interval (ISI) of 20, 50 or 150 ms. The intraclass correlation (ICC) was computed for each participant between the ERP to a single tone and the ERP to the tone pair. A high ICC indicates that the brain response to a tone pair is similar to that for a single tone. ICCs were significantly higher at short than at long ISIs. At 50‐ms ISI, ICCs were higher for younger than older participants. Age and ISI interacted with SLI status: ERPs of older participants with SLI differed from age‐matched controls, and resembled ERPs of younger controls, consistent with a theory of immature auditory processing in SLI.
Infants’ attribution of a goal to a morphologically unfamiliar agent
Authors: Shimizu Y. Alpha , Johnson Susan C.
Published: August 2004

How do infants identify the psychological actors in their environments? Three groups of 12‐month‐old infants were tested for their willingness to encode a simple approach behavior as goal‐directed as a function of whether it was performed by (1) a human hand, (2) a morphologically unfamiliar green object that interacted with a confederate and behaved intentionally, or (3) the same unfamiliar green object that behaved in a matched, but apparently random manner. Using a visual habituation technique, only infants in the first two conditions were found to encode the approach behavior as goal‐directed. Thus infants appear able to attribute goals to non‐human, even unfamiliar agents. These results imply that by the end of the first year of life infants have a broad notion of what counts as an agent that cannot easily be reduced to humans, objects that are perceptually similar to humans, or objects that display self‐propulsion.
The Thatcher illusion and face processing in infancy
Authors: Bertin Evelin , Bhatt Ramesh S.
Published: August 2004

Adults readily detect changes in face patterns brought about by the inversion of eyes and mouth when the faces are viewed upright but not when they are viewed upside down. Research suggests that this illusion (the Thatcher illusion) is caused by the interfering effects of face inversion on the processing of second‐order relational information (fine spatial information such as the distance between the eyes). In the current study, 6‐month‐olds discriminated ‘thatcherized’ faces when they were viewed upright but not when they were viewed upside down. These results are consistent with the notion that 6‐month‐olds are sensitive to second‐order relational information while processing faces.
Imitation in neonatal chimpanzees (Pan troglodytes)
Authors: Myowa‐Yamakoshi Masako , Tomonaga Masaki , Tanaka Masayuki , Matsuzawa Tetsuro
Published: August 2004

This paper provides evidence for imitative abilities in neonatal chimpanzees (Pan troglodytes), our closest relatives. Two chimpanzees were reared from birth by their biological mothers. At less than 7 days of age the chimpanzees could discriminate between, and imitate, human facial gestures (tongue protrusion and mouth opening). By the time they were 2 months old, however, the chimpanzees no longer imitated the gestures. They began to perform mouth opening frequently in response to any of the three facial gestures presented to them. These findings suggest that neonatal facial imitation is most likely an innate ability, developed through natural selection in humans and in chimpanzees. The relationship between the disappearance of neonatal imitation and the development of social communicative behavior is discussed from an evolutionary perspective.
The pre‐eminent Pre‐Raphaelite: Revisiting Rossetti
Authors: Cruise Colin
Published: August 2004

Books reviewed:

William E. Fredeman (ed.), The Correspondence of Dante Gabriel Rossetti: The Formative Years, 1835–54 [Vol. I]

Pre‐Raphaelite and other Masters: The Andrew Lloyd Webber Collection

Julian Treuherz et al., Dante Gabriel Rossetti

Tim Barringer, Reading the Pre‐Raphaelites

Julie F. Codell, The Victorian Artist: Artists' Lifewritings in Britain ca. 1870–1910

Angela Thirlwell, William and Lucy: The Other Rossettis
Saving Postmodernism's Soul: Bill Viola's The Passions
Authors: Packwood David
Published: August 2004

Book reviewed:

John Walsh (ed.), Bill Viola: The Passions
Foreigners in Receptive Lands
Authors: Somerville Rosa
Published: August 2004

Books reviewed:

Sandra de László (ed.), A Brush with Grandeur — Philip Alexius de László 1869–1937

Richard Ormond and Elaine Kilmurray, John Singer Sargent: The Later Portraits, Volume III
Away from the Motif
Authors: Lynton Norbert
Published: August 2004

Book reviewed:

Jeffrey Weiss, Valerie J. Fletcher and Kathryn A. Tuma, Picasso: The Cubist Portraits of Fernande Olivier
VOTS: VOlume doTS as a Point‐Based Representation of Volumetric Data
Authors: Grimm Sören , Bruckner Stefan , Kanitsar Armin , Gröller Eduard
Published: August 2004

We present Volume dots (Vots), a new primitive for volumetric data modelling, processing, and rendering. Vots are a point‐based representation of volumetric data. An individual Vot is specified by the coefficients of a Taylor series expansion, i.e. the function value and higher order derivatives at a specific point. A Vot does not only represent a single sample point, it represents the underlying function within a region. With the Vots representation we have a more intuitive and high‐level description of the volume data. This allows direct analytical examination and manipulation of volumetric datasets. Vots enable the representation of the underlying scalar function with specified precision. User‐centric importance sampling is also possible, i.e., unimportant volume parts are still present but represented with just very few Vots. As proof of concept, we show Maximum Intensity Projection based on Vots.

Categories and Subject Descriptors (according to ACM CCS): I.3.6 [Computer Graphics]: Graphics Data Structures and Data Types
Immersive Integration of Physical and Virtual Environments
Authors: Fuchs Henry
Published: August 2004

We envision future work and play environments in which the user's computing interface is more closely integrated with the physical surroundings than today's conventional computer display screens and keyboards.We are working toward realizable versions of such environments, in which multiple video projectors and digital cameras enable every visible surface to be both measured in 3D and used for display. If the 3D surface positions were transmitted to a distant location, they may also enable distant collaborations to become more like working in adjacent offices connected by large windows. With collaborators at the University of Pennsylvania, Brown University, Advanced Network and Services, and the Pittsburgh Supercomputing Center, we at Chapel Hill have been working to bring these ideas to reality. In one system, depth maps are calculated from streams of video images and the resulting 3D surface points are displayed to the user in head‐tracked stereo. Among the applications we are pursuing for this tele‐presence technology, is advanced training for trauma surgeons by immersive replay of recorded procedures. Other applications display onto physical objects, to allow more natural interaction with them ``painting'' a dollhouse, for example. More generally, we hope to demonstrate that the principal interface of a future computing environment need not be limited to a screen the size of one or two sheets of paper. Just as a useful physical environment is all around us, so too can the increasingly ubiquitous computing environment be all around us ‐integrated seamlessly with our physical surroundings.
Applied Geometry:Discrete Differential Calculus for Graphics
Authors: Desbrun Mathieu
Published: August 2004

Geometry has been extensively studied for centuries, almost exclusively from a differential point of view. However, with the advent of the digital age, the interest directed to smooth surfaces has now partially shifted due to the growing importance of discrete geometry. From 3D surfaces in graphics to higher dimensional manifolds in mechanics, computational sciences must deal with sampled geometric data on a daily basis‐hence our interest in Applied Geometry.

In this talk we cover different aspects of Applied Geometry. First, we discuss the problem of Shape Approximation, where an initial surface is accurately discretized (i.e., remeshed) using anisotropic elements through error minimization. Second, once we have a discrete geometry to work with, we briefly show how to develop a full‐ blown discrete calculus on such discrete manifolds, allowing us to manipulate functions, vector fields, or even tensors while preserving the fundamental structures and invariants of the differential case. We will emphasize the applicability of our discrete variational approach to geometry by showing results on surface parameterization, smoothing, and remeshing, as well as virtual actors and thin‐shell simulation.

Joint work with: Pierre Alliez (INRIA), David Cohen‐Steiner (Duke U.), Eitan Grinspun (NYU), Anil Hirani (Caltech), Jerrold E. Marsden (Caltech), Mark Meyer (Pixar), Fred Pighin (USC), Peter Schröder (Caltech), Yiying Tong (USC).
Approximate Soft Shadows win an Image‐Space Flood‐Fill Algorithm
Authors: Arvo Jukka , Hirvikorpi Mika , Tyystjärvi Joonas
Published: August 2004

Most former soft shadow algorithms have either suffered from restricted self‐shadowing capabilities, been too slow for interactive applications, or could only be used with a limited types of geometry. In this paper, we propose an efficient image‐based approach for computing soft shadows. Our method is based on shadow mapping and provides the associated benefits. We use pixel‐based visibility computations for rendering penumbra regions directly into the screen‐space. This is accomplished by using a modified flood‐fill algorithm which enables us to implement the algorithm using programmable graphics hardware. Even though the resulting images are most often high quality, we do not claim that the proposed method is physically correct. The computation time and memory requirements for soft shadows depend on image resolution and the number of lights, not geometric scene complexity.

Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Picture/Image Generation I.3.7 [Three‐Dimensional Graphics and Realism]: Color, shading, shadowing, and texture
Real‐time Light Animation
Authors: Sbert Mateu , Szécsi László , Szirmay‐Kalos László
Published: August 2004

Light source animation is a particularly hard field of real‐time global illumination algorithms since moving light sources result in drastic illumination changes and make coherence techniques less effective. However, the animation of small (point‐like) light sources represents a special but practically very important case, for which the reuse of the results of other frames is possible. This paper presents a fast light source animation algorithm based on the virtual light sources illumination method. The speed up is close to the length of the animation, and is due to reusing paths in all frames and not only in the frame where they were obtained. The possible applications of this algorithm are the lighting design and systems to convey shape and features with relighting.
SMARTPAPER: An Interactive and User Friendly Sketching System
Authors: Shesh Amit , Chen Baoquan
Published: August 2004

This paper describes an interactive sketching system for 3D design/modeling that diverts from the conventional menu‐and‐button interfaces of CAD tools. The system, dubbed SMARTPAPER, offers a unified sketching environment that supports direct sketching as well as gestured sketching with more emphasis on the former to encourage natural sketching styles. SMARTPAPER also provides a unified 2D and 3D drawing domain by allowing the user to sketch directly on a 3D model in addition to the usual 2D sketching from scratch. A natural sketching experience is offered by supporting casual sketching consisting of wiggly, discontinuous, overlapping strokes. The system is empowered by an array of seamlessly integrated 2D and 3D features such as 2D sketch cleaning, 3D reconstruction from 2D sketch, 3D transformations, sketching on 3D, and conventional 3D CSG operations like cutting and joining. The key to the success of SMARTPAPER is efficient and robust 3D reconstruction from a single freehand 2D sketch with minimal hints. We have employed and improved Lipson's optimization method, originally designed for offline reconstruction of engineering drawings, in our interactive system by leveraging additional clues obtained by interaction during sketching.

Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Interaction Techniques, Pen‐based Interaction
Fast Surface Modelling Using a 6th Order PDE
Authors: Zhang Jian. J. , You L. H.
Published: August 2004

Although the control‐point based parametric approach is used most widely in free‐form surface modelling, complementary techniques co‐exist to meet various specialised requirements. The partial differential equation (PDE) based modelling approach is especially suitable for satisfying surface boundary constraints. They are also effective for the generation of families of free‐form surfaces, which share a common base and differ in their secondary features. In this paper, we present a fast surface modelling method using a sixth order PDE. This PDE provides enough degrees of freedom not only to accommodate tangent, but also curvature boundary conditions and offers more shape control parameters to serve as user controls for the manipulation of surface shapes. In order to achieve real‐time performance, we have constructed a surface function and developed a high‐precision approximate solution to the 6th order PDE. Unlike some existing PDE‐based techniques, this resolution method can satisfy the boundary conditions exactly, and is able to create free‐form surfaces as fast and almost as accurately as the closed‐form (analytical) solutions. Due to the fact that it has sufficient degrees of freedom to accommodate the continuity of 3‐sided and 4‐sided surface patches at their boundaries, this method is able to model complex surfaces consisting of multiple patches. Compared with existing PDE‐based modelling methods, this method is both fast and can solve a larger class of surface modelling problems.

Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Curves, surfaces, solid, and object representations; physically based modelling
Dupin Cyclide Blends Between Quadric Surfaces for Shape Modeling
Authors: Foufou Sebti , Garnier Lionel
Published: August 2004

We introduce a novel method to define Dupin cyclide blends between quadric primitives. Dupin cyclides are non‐spherical algebraic surfaces discovered by French mathematician Pierre‐Charles Dupin at the beginning of the 19th century. As a Dupin cyclide can be fully characterized by its principal circles, we have focussed our study on how to determine principal circles tangent to both quadrics being blended. This ensures that the Dupin cyclide we are constructing constitutes a

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blend. We use the Rational Quadratic Bézier Curve (RQBC) representation of circular arcs to model the principal circles, so the construction of each circle is reduced to the determination of the three control points of the RQBC representing the circle.

In this work, we regard the blending of two quadric primitives A and B as two complementary blending operations: primitive A‐cylinder and cylinder‐primitive B; two Dupin cyclides and a cylinder are then defined for each blending operation. In general the cylinder is not useful and may be reduced to a simple circle. A complete shape design example is presented to illustrate the modeling of Eurographics'04 Hugo using a limited number of quadrics combined using Dupin cyclide blends.

Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Computational Geometry and Object Modeling
A Biophysically‐Based Spectral Model of Light Interaction with Human Skin
Authors: Krishnaswamy Aravind , Baranoski Gladimir V.G.
Published: August 2004

Despite the notable progress in physically‐based rendering, there is still a long way to go before we can automatically generate predictable images of biological materials. In this paper, we address an open problem in this area, namely the spectral simulation of light interaction with human skin. We propose a novel biophysically based model that accounts for all components of light propagation in skin tissues, namely surface reflectance, subsurface reflectance and transmittance, and the biological mechanisms of light absorption by pigments in these tissues. The model is controlled by biologically meaningful parameters, and its formulation, based on standard Monte Carlo techniques, enables its straightforward incorporation into realistic image synthesis frameworks. Besides its biophysically‐based nature, the key difference between the proposed model and the existing skin models is its comprehensiveness, i.e., it computes both spectral (reflectance and transmittance) and scattering (bidirectional surface‐scattering distribution function) quantities for skin specimens. In order to assess the predictability of our simulations, we evaluate their accuracy by comparing results from the model with actual skin measured data. We also present computer generated images to illustrate the flexibility of the proposed model with respect to variations in the biological input data, and its applicability not only in the predictive image synthesis of different skin tones, but also in the spectral simulation of medical conditions.

Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three‐Dimensional Graphics and Realism
Simulating and modeling lichen growth
Authors: Desbenoit Brett , Galin Eric , Akkouche Samir
Published: August 2004

This paper presents a system for modeling lichens and simulating their propagation and growth in a virtual scene. Lichens colonize almost every substrate in nature and play an important role in the visual appearance of a natural object. The propagation of lichens over the substrate is performed by an Open Diffusion Limited Aggregation model constrained by the characteristics of the environment. The designer can control the development of lichens with simple parameters. Rendering the complex geometry and texture of lichens is achieved by instantiating three dimensional lichen models stored in an atlas of shapes created after real world images. The lichens obtained by our approach considerably increase the realism of complex natural scenes.

Categories and Subject Descriptors (according to ACMCCS):I.3.3 [Computer Graphics]:Three‐Dimensional Graphics and Realism
Implicit Visualization and Inverse Modeling of Growing Trees
Authors: Galbraith Callum , Mündermann Lars , Wyvill Brian
Published: August 2004

A method is proposed for photo‐realistic modeling and visualization of a growing tree. Recent visualization methods have focused on producing smoothly blending branching structures, however, these methods fail to account for the inclusion of non‐smooth features such as branch bark ridges and bud scale scars. These features constitute an important visual aspect of a living tree, and are also observed to vary over time. The proposed method incorporates these features by using an hierarchical implicit modeling system, which provides a variety of tools for combining surface components in both smooth and non smooth configurations. A procedural interface to this system supports the use of inverse modeling, which is a global‐to‐local methodology, where the local properties of plant organs are described in terms of their global position within the tree architecture. Inverse modeling is used to define both the tree structure at any time, and a continuous developmental sequence for the tree from a seedling. These techniques provide an intuitive paradigm for the definition of complex tree growth sequences and their subsequent visualization, based solely on observed phenomena. Thus, a key advantage is that they do not require any knowledge of, or simulation of, the underlying biological processes.

Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Curve, surface, solid, and object representations I.3.7 [Computer Graphics]: Animation
A Physically‐Based Model for Rendering Realistic Scratches
Authors: Bosch Carles , Pueyo Xavier , Mérillou Stéphane , Ghazanfarpour Djamchid
Published: August 2004

Individually visible scratches, also called isolated scratches, are very common in real world surfaces. Although their microgeometry is not visible, they are individually perceptible by the human eye, lying into a representation scale between BRDF and texture. In order to simulate this kind of scratches in synthetic images we need to know their position over the surface (texture scale), so we can determine where to use the specific scratch BRDF instead of the ordinary surface BRDF. Computing the BRDF of a scratch is difficult because it depends on the scratch's invisible microgeometry. In this paper, we propose a new physically based model to derive this microgeometry by simulating the formation process of scratches. We allow specifying intuitively the parameters involved in the process such as the scratching tool, the penetration forces, and the material properties of the object. From these parameters, we derive the microgeometries of the scratches by taking into account the real behaviour of the process. This behaviour has been determined by analysing existing models in the field of materials engineering and some ``scratch tests'' that we performed on metals. Our method has the advantages of easily simulating scratches with a wide range of microgeometries and taking into account the variability of their microgeometry along the scratch path. Another contribution is related to the location of the scratches over the surface. Instead of using an image of the paths as in previous work, we present a new representation based on curves defining the paths. This offers an independence on the image resolution or the distance from the observer and accurately provides the scratch direction in order to compute scratch BRDFs.

Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Color, shading, shadowing, and texture.
Single‐Strip Triangulation of Manifolds with Arbitrary Topology
Authors: Gopi M. , Eppstien David
Published: August 2004

Triangle strips have been widely used for efficient rendering. It is NP‐complete to test whether a given triangulated model can be represented as a single triangle strip, so many heuristics have been proposed to partition models into few long strips. In this paper, we present a new algorithm for creating a single triangle loop or strip from a triangulated model. Our method applies a dual graph matching algorithm to partition the mesh into cycles, and then merges pairs of cycles by splitting adjacent triangles when necessary. New vertices are introduced at midpoints of edges and the new triangles thus formed are coplanar with their parent triangles, hence the visual fidelity of the geometry is not changed. We prove that the increase in the number of triangles due to this splitting is 50% in the worst case, however for all models we tested the increase was less than 2%. We also prove tight bounds on the number of triangles needed for a single‐strip representation of a model with holes on its boundary. Our strips can be used not only for efficient rendering, but also for other applications including the generation of space filling curves on a manifold of any arbitrary topology.

Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Geometric algorithms, Triangulation, Stripification. G.2.2 [Graph algorithms]: Hamiltonian Path, Hamiltonian Cycle, Perfect Matching.
Approximated Centroidal Voronoi Diagrams for Uniform Polygonal Mesh Coarsening
Authors: Valette Sébastien , Chassery Jean‐Marc
Published: August 2004

We present a novel clustering algorithm for polygonal meshes which approximates a Centroidal Voronoi Diagram construction. The clustering provides an efficient way to construct uniform tessellations, and therefore leads to uniform coarsening of polygonal meshes, when the output triangulation has many fewer elements than the input mesh. The mesh topology is also simplified by the clustering algorithm. Based on a mathematical framework, our algorithm is easy to implement, and has low memory requirements. We demonstrate the efficiency of the proposed scheme by processing several reference meshes having up to 1 million triangles and very high genus within a few minutes on a low‐ end computer.
Anisotropic Filtering of Non‐Linear Surface Features
Authors: Hildebrandt Klaus , Polthier Konrad
Published: August 2004

A new method for noise removal of arbitrary surfaces meshes is presented which focuses on the preservation and sharpening of non‐linear geometric features such as curved surface regions and feature lines. Our method uses a prescribed mean curvature flow (PMC) for simplicial surfaces which is based on three new contributions: 1. the definition and efficient calculation of a discrete shape operator and principal curvature properties on simplicial surfaces that is fully consistent with the well‐known discrete mean curvature formula, 2. an anisotropic discrete mean curvature vector that combines the advantages of the mean curvature normal with the special anisotropic behaviour along feature lines of a surface, and 3. an anisotropic prescribed mean curvature flow which converges to surfaces with an estimated mean curvature distribution and with preserved non‐linear features. Additionally, the PMC flow prevents boundary shrinkage at constrained and free boundary segments.
Computing Maximal Tiles and Application to Impostor‐Based Simplification
Authors: Andujar C. , Brunet P. , Chica A. , Navazo I. , Rossignac J. , Vinacua A.
Published: August 2004

The computation of the largest planar region approximating a 3D object is an important problem with wide applications in modeling and rendering. Given a voxelization of the 3D object, we propose an efficient algorithm to solve a discrete version of this problem. The input of the algorithm is the set of grid edges connecting the interior and the exterior of the object (called sticks). Using a voting‐based approach, we compute the plane that slices the largest number of sticks and is orientation‐compatible with these sticks. The robustness and efficiency of our approach rests on the use of two different parameterizations of the planes with suitable properties. The first of these is exact and is used to retrieve precomputed local solutions of the problem. The second one is discrete and is used in a hierarchical voting scheme to compute the global maximum. This problem has diverse applications that range from finding object signatures to generating simplified models. Here we demonstrate the merits of the algorithm for efficiently computing an optimized set of textured impostors for a given polygonal model.

Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Computational Geometry and Object Modeling
A System for View‐Dependent Animation
Authors: Chaudhuri Parag , Kalra Prem , Banerjee Subhashis
Published: August 2004

In this paper, we present a novel system for facilitating the creation of stylized view‐dependent 3D animation. Our system harnesses the skill and intuition of a traditionally trained animator by providing a convivial sketch based 2D to 3D interface. A base mesh model of the character can be modified to match closely to an input sketch, with minimal user interaction. To do this, we recover the best camera from the intended view direction in the sketch using robust computer vision techniques. This aligns the mesh model with the sketch. We then deform the 3D character in two stages ‐ first we reconstruct the best matching skeletal pose from the sketch and then we deform the mesh geometry. We introduce techniques to incorporate deformations in the view‐dependent setting. This allows us to set up view‐dependent models for animation.

Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three‐Dimensional Graphics and Realism ‐ Animation

Our system takes as input a sketch (a), and a base mesh model (b), then recovers a camera to orient the base mesh (c), then reconstructs the skeleton pose (d), and finally deforms the mesh to find the best possible match with the sketch (e).

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High Quality Hatching
Authors: Zander Johannes , Isenberg Tobias , Schlechtweg Stefan , Strothotte Thomas
Published: August 2004

Hatching lines are often used in line illustrations to convey tone and texture of a surface. In this paper we present methods to generate hatching lines from polygonal meshes and render them in high quality either at interactive rates for on‐screen display or for reproduction in print. Our approach is based on local curvature information that is integrated to form streamlines on the surface of the mesh. We use a new algorithm that provides an even distribution of these lines. A special processing of these streamlines ensures high quality line rendering for both intended output media later on. While the streamlines are generated in a preprocessing stage, hatching lines are rendered either for vector‐based printer output or on‐screen display, the latter allowing for interaction in terms of changing the view parameters or manipulating the entire line shading model at run‐time using a virtual machine.

Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Picture/Image Generation—Display algorithms; I.3.3 [Computer Graphics]: Picture/Image Generation—Line and curve generation

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Virtual Drypoint by a Model‐driven Strategy
Authors: Tasaki Daisuke , Mizuno Shinji , Okada Minoru
Published: August 2004

In this paper we propose a method to synthesize a virtual copperplate print image based on physical model as a non‐photorealistic rendering in Computer Graphics. In particular we pick out the drypoint from many existing copperplate printing techniques. A drypoint print has a remarkable feature that ridged burrs are arising out of the copperplate and the printed lines are slightly ragged and fuzzy. Our method consists of four sub‐processes: plate making, ink applying, wiping and printing. Each process simulates the physical actions and phenomena observed in the actual copperplate printing. In this study we use a small‐scale print and an actual print created by a real copperplate artist for some experiments to indicate effects and availability of proposed method to synthesize a print image with the feature of drypoint.

Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three‐Dimensional Graphics and Realism
The Design of an Inexpensive Very High Resolution Scan Camera System
Authors: Wang Shuzhen , Heidrich Wolfgang
Published: August 2004

We describe a system for transforming an off‐the‐shelf flatbed scanner into a $200 scan backend for large format cameras. While we describe both software and hardware aspects, the focus of the paper is on software issues such as color calibration and removal of scanner artifacts. With current scanner technology, the resulting camera system is capable of taking black&white, color, or near‐infrared photographs with up to 490 million pixels. Our analysis shows that we achieve actual optical resolutions close to the theoretical maximum, and that color reproduction is comparable to commercial camera systems. We believe that the camera system described here has many potential applications in image‐based modeling and rendering, cultural heritage projects, and professional digital photography.
Quadric Transfer for Immersive Curved Screen Displays
Authors: Raskar Ramesh , van Baar Jeroen , Willwacher Thomas , Rao Srinivas
Published: August 2004

Curved screens are increasingly being used for high‐resolution immersive visualization environments. We describe a new technique to display seamless images using overlapping projectors on curved quadric surfaces such as spherical or cylindrical shape. We exploit a quadric image transfer function and show how it can be used to achieve sub‐pixel registration while interactively displaying two or three‐dimensional datasets for a head‐tracked user. Current techniques for automatically registered seamless displays have focused mainly on planar displays. On the other hand, techniques for curved screens currently involve cumbersome manual alignment to make the installation conform to the intended design. We show a seamless real‐time display system and discuss our methods for smooth intensity blending and efficient rendering.

Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three‐Dimensional Graphics and Realism‐ Virtual reality
Topological Construction and Visualization of Higher Order 3D Vector Fields
Authors: Weinkauf Tino , Theisel Holger , Hege Hans‐Christian , Seidel Hans‐Peter
Published: August 2004

We present the first algorithm for constructing 3D vector fields based on their topological skeleton. The skeleton itself is modeled by interactively moving a number of control polygons. Then a piecewise linear vector field is automatically constructed which has the same topological skeleton as modeled before. This approach is based on a complete segmentation of the areas around critical points into sectors of different flow behavior. Based on this, we present the first approach to visualizing higher order critical points of 3D vector fields.

Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Line and Curve Generation I.3.7 [Computer Graphics]: Three‐Dimensional Graphics and Realism
Dye Advection Without the Blur: A Level‐Set Approach for Texture‐Based Visualization of Unsteady Flow
Authors: Weiskopf D.
Published: August 2004

Dye advection is an intuitive and versatile technique to visualize both steady and unsteady flow. Dye can be easily combined with noise‐based dense vector field representations and is an important element in user‐centric visual exploration processes. However, fast texture‐based implementations of dye advection rely on linear interpolation operations that lead to severe diffusion artifacts. In this paper, a novel approach for dye advection is proposed to avoid this blurring and to achieve long and clearly defined streaklines or extended streak‐like patterns. The interface between dye and background is modeled as a level‐set within a signed distance field. The level‐set evolution is governed by the underlying flow field and is computed by a semi‐Lagrangian method. A reinitialization technique is used to counteract the distortions introduced by the level‐set evolution and to maintain a level‐set function that represents a local distance field. This approach works for 2D and 3D flow fields alike. It is demonstrated how the texture‐based level‐set representation lends itself to an efficient GPU implementation and therefore facilitates interactive visualization.

Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Picture/Image Generation I.3.7 [Computer Graphics]: Three‐Dimensional Graphics and Realism
Instant Volumetric Understanding with Order‐Independent Volume Rendering
Authors: Mora Benjamin , Evert David S.
Published: August 2004

Rapid, visual understanding of volumetric datasets is a crucial outcome of a good volume rendering application, but few current volume rendering systems deliver this result. Our goal is to reduce the volumetric surfing that is required to understand volumetric features by conveying more information in fewer images. In order to achieve this goal, and in contrast with most current methods which still use optical models and alpha blending, our approach reintroduces the order‐independent contribution of every sample along the ray in order to have an equiprobable visualization of all the volume samples. Therefore, we demonstrate how order independent sampling can be suitable for fast volume understanding, show useful extensions to MIP and X‐ray like renderings, and, finally, point out the special advantage of using stereo visualization in these models to circumvent the lack of depth cues.

Categories and Subject Descriptors: I.3.3 [Computer Graphics]: Picture/Image, Generation,

I.3.7 [Computer Graphics]: Three‐Dimensional graphics and realism.
Way‐Finder: guided tours through complex walkthrough models
Authors: Andújar C. , Vázquez P. , Fairén M.
Published: August 2004

The exploration of complex walkthrough models is often a difficult task due to the presence of densely occluded regions which pose a serious challenge to online navigation. In this paper we address the problem of algorithmic generation of exploration paths for complex walkthrough models. We present a characterization of suitable properties for camera paths and we discuss an efficient algorithm for computing them with little or no user intervention. Our approach is based on identifying the free‐space structure of the scene (represented by a cell and portal graph) and an entropy‐based measure of the relevance of a view‐point. This metric is key for deciding which cells have to be visited and for computing critical way‐points inside each cell. Several results on different model categories are presented and discussed.
Crowd of Virtual Humans: a New Approach for Real Time Navigation in Complex and Structured Environments
Authors: Lamarche Fabrice , Donikian Stéphane
Published: August 2004

The navigation activity is an every day practice for any human being capable of locomotion. Our objective in this work is to reproduce this crucial human activity inside virtual environments. Putting together the high complexity of a realistic environment such as a city, a big amount of virtual humans and the real‐time constraint requires to optimize each aspect of the animation process. In this paper, we present a suitable topological structuring of the geometric environment to allow fast path finding as well as an efficient reactive navigation algorithm for virtual humans evolving inside a crowd.
Scalable behaviors for crowd simulation
Authors: Sung Mankyu , Gleicher Michael , Chenney Stephen
Published: August 2004

Crowd simulation for virtual environments offers many challenges centered on the trade‐offs between rich behavior, control and computational cost. In this paper we present a new approach to controlling the behavior of agents in a crowd. Our method is scalable in the sense that increasingly complex crowd behaviors can be created without a corresponding increase in the complexity of the agents. Our approach is also more authorable; users can dynamically specify which crowd behaviors happen in various parts of an environment. Finally, the character motion produced by our system is visually convincing. We achieve our aims with a situation‐based control structure. Basic agents have very limited behaviors. As they enter new situations, additional, situation‐specific behaviors are composed on the fly to enable agents to respond appropriately. The composition is done using a probabilistic mechanism. We demonstrate our system with three environments including a city street and a theater.

Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Animation
Real‐time Rigid Body Simulation for Haptic Interactions Based on Contact Volume of Polygonal Objects
Authors: Hasegawa S. , Sato M.
Published: August 2004

This paper proposes a new method for real‐time rigid body simulations for haptic interactions based on a penalty method regarding contact volume. Analytical methods for calculation of contact forces require too much time to maintain fast update rates for haptic controls. In addition, they prohibit direct connection of haptic interfaces.

Penalty methods, which employ spring‐damper models for calculation of contact forces, offer a very rapid rate of iterations. In addition, they permit direct connection of haptic interfaces. Penalty methods are good for haptic interactions. However, previous penalty methods do not regard distribution of contact forces over the contact area. For that reason, they can't calculate normal and friction forces on face‐face contacts correctly.

We propose a distributed spring‐damper model on a contact area to solve these problems. We analyze three‐dimensional geometries of the intersecting portion on the polyhedral objects. Then, we integrate forces and torques of distributed spring‐damper models.

We implement a proposed simulator and compare it with a point‐based penalty method and constraint method. The comparison shows that the proposed simulator improves accuracy of the simulation of face‐face contact and friction forces and the simulation speed. In addition, we attach a six degree‐of‐freedom (6‐DOF) haptic interface to the simulator. Users can feel 6‐DOF force feedback and input 6‐DOF motions.

Categories and Subject Descriptors (according to ACM CCS): I.6.5 [Model Development]: Modeling methodologies, H.5.2 [User Interfaces]: Haptic I/O, I.3.6 [Methodology and Techniques]: Interaction techniques