Virtual reality systems often make use of spatially tracked handheld props in the form of controllers or specialized objects to add realism and interaction. Tracking these objects today relies on the use of expensive, bulky, and power-consuming trackers that must be attached to an object. We propose a passive tracking technique that works with existing low-cost, off-the-shelf optical tracking components and is capable of turning any object into a tracked virtual reality prop. Our method utilizes paper-thin retro-reflective markers that can be placed in any free-form on everyday objects. The proof-of-concept prototype acts as a simple add-on for an existing tracking system and requires only a minimal amount of compute overhead. We demonstrate that our method allows bringing physical real-world objects to virtual worlds with ease, and provides an object identification technique using patterned retro-reflective markers.

This article introduces a method for accurately computing the visible contours of a smooth 3D surface for stylization. This is a surprisingly difficult problem, and previous methods are prone to topological errors, such as gaps in the outline. Our approach is to generate, for each viewpoint, a new triangle mesh with contours that are topologically equivalent and geometrically close to those of the original smooth surface. The contours of the mesh can then be rendered with exact visibility. The core of the approach is Contour Consistency, a way to prove topological equivalence between the contours of two surfaces. Producing a surface tessellation that satisfies this property is itself challenging; to this end, we introduce a type of triangle that ensures consistency at the contour. We then introduce an iterative mesh generation procedure, based on these ideas. This procedure does not fully guarantee consistency, but errors are not noticeable in our experiments. Our algorithm can operate on any smooth input surface representation; we use Catmull-Clark subdivision surfaces in our implementation. We demonstrate results computing contours of complex 3D objects, on which our method eliminates the contour artifacts of other methods.

Skilled artists, using traditional media or modern computer painting tools, can create a variety of expressive styles that are very appealing in still images, but have been unsuitable for animation. The key difficulty is that existing techniques lack adequate temporal coherence to animate these styles effectively. Here we augment the range of practical animation styles by extending the guided texture synthesis method of Image Analogies [Hertzmann et al. 2001] to create temporally coherent animation sequences. To make the method art directable, we allow artists to paint portions of keyframes that are used as constraints. The in-betweens calculated by our method maintain stylistic continuity and yet change no more than necessary over time.

A wide variety of non-photorealistic rendering techniques make use of random variation in the placement or appearance of primitives. In order to avoid the "shower-door" effect, this random variation should move with the objects in the scene. Here we present coherent noise tailored to this purpose. We compute the coherent noise with a specialized filter that uses the depth and velocity fields of a source sequence. The computation is fast and suitable for interactive applications like games.

Local image histograms contain a great deal of information useful for applications in computer graphics, computer vision and computational photography. Making use of that information has been challenging because of the expense of computing histogram properties over large neighborhoods. Efficient algorithms exist for some specific computations like the bilateral filter, but not others. Here, we present an efficient and practical method for computing accurate derivatives and integrals of locally-weighted histograms over large neighborhoods. The method allows us to compute the location, height, width and integral of all local histogram modes at interactive rates. Among other things, it enables the first constant-time isotropic median filter, robust isotropic image morphology operators, an efficient "dominant mode" filter and a non-iterative alternative to the mean shift. In addition, we present a method to combat the over-sharpening that is typical of histogram-based edge-preserving smoothing. This post-processing step should make histogram-based filters not only fast and efficient, but also suitable for a variety of new applications.

Oscillatory motion is ubiquitous in computer graphics, yet existing animation techniques are ill-suited to its authoring. We introduce a new type of spline for this purpose, known as a "Wiggly Spline." The spline generalizes traditional piecewise cubics when its resonance and damping are set to zero, but creates oscillatory animation when its resonance and damping are changed. The spline provides a combination of direct manipulation and physical realism. To create overlapped and propagating motion, we generate phase shifts of the Wiggly Spline, and use these to control appropriate degrees of freedom in a model. The phase shifts can be created directly by procedural techniques or through a paint-like interface. A further option is to derive the phase shifts statistically by analyzing a time-series of a simulation. In this case, the Wiggly Spline makes it possible to canonicalize a simulation, generalize it by providing frequency and damping controls and control it through direct manipulation.

The purpose of the workshop is to convene researchers, developers, and government and industrial users of software security assurance (SSA) tools to refine the taxonomy of flaws and the taxonomy of SSA tool functions, converge on which SSA functions should first have specifications and tests developed, gather SSA tool developers for "target practice" on the reference datasets, and identify gaps or requirements for research in SSA functions. There are contributions describing basic research, novel applications, and experience relevant to SSA tools and their evaluation. The reference datasets are code with known flaws and vulnerabilities, with corresponding correct versions, to be used as references for tool testing, to make research easier, and to be a standard of evaluation. Tools ranging from commercial products to university projects "shoot holes" in the datasets to suggest extensions, improvements, etc. This is a U.S. National Institute of Standards and Technology SAMATE (http://samate.nist.gov/) workshop.

Deficient cloth-to-cloth collision response is the most serious shortcoming of most cloth simulation systems. Past approaches to cloth-cloth collision have used history to decide whether nearby cloth regions have interpenetrated. The biggest pitfall of history-based methods is that an error anywhere along the way can give rise to persistent tangles. This is a particularly serious issue for production character animation, because characters' bodies routinely self-intersect, for instance in the bend of an elbow or knee, or where the arm or hand rests against the body. Cloth that becomes pinched in these regions is often forced into jagged self-intersections that defeat history-based methods, leaving a tangled mess when the body parts separate. This paper describes a history-free cloth collision response algorithm based on global intersection analysis of cloth meshes at each simulation step. The algorithm resolves tangles that arise during pinching as soon as the surrounding geometry permits, and also resolves tangled initial conditions. The ability to untangle cloth after pinching is not sufficient, because standard cloth-solid collision algorithms handle pinches so poorly that they often give rise to visible flutters and other simulation artifacts during the pinch. As a companion to the global intersection analysis method, we present a cloth-solid collision algorithm called collision flypapering, that eliminates these artifacts. The two algorithms presented have been used together extensively and successfully in a production animation environment.

The creation of believable and endearing characters in computer graphics presents a number of technical challenges, including the modeling, animation and rendering of complex shapes such as heads, hands, and clothing. Traditionally, these shapes have been modeled with NURBS surfaces despite the severe topological restrictions that NURBS impose. In order to move beyond these restrictions, we have recently introduced subdivision surfaces into our production environment. Subdivision surfaces are not new, but their use in high-end CG production has been limited.

This panel will address the technical, economic and marketing hurdles that inhibit the widespread use of cloth/clothing modeling, design and animation technology.Many of the fundamental technologies needed to support cloth modeling have already been developed.Still, we do not see computer-animated characters wearing realistic clothing, and clothing designers are not creating new fashions with computer-based 3-D design systems.The CAD industry is capable of providing the systems for designing the Boeing 777, but almost none of the clothing we wear is designed with 3-D CAD tools.The panel will explore the reasons that the design of cloth and clothing, a material that has been a part of the human experience for thousands of years, has not yet been fully computerized.A variety of issues related to cloth/clothing modeling will be explored.Are there fundamental technological barriers preventing us from fully deploying computer technology when modeling, designing, or animating cloth/clothing?Have the technical problems been solved and our computers are just not fast enough?Do we simply need good user interfaces to solve this difficult modeling problem?Is realism always important when modeling cloth?Does computer-based manufacturing place special demands on cloth modeling?Are designers, artists and clothing makers resisting the computerization of their "black art"?Can the average user even afford to do cloth modeling?Is the technology too expensive?These are some of the questions that the panelists will address. Can We Get There From Here?: Current Challenges in Cloth Design, Modeling and AnimationOrganizer

In previous work, we presented an algorithm to accelerate z-buffer rendering of enormously complex scenes. Here, we extend the approach to antialiased rendering with an algorithm that guarantees that each pixel of the output image is within a user-specified error tolerance of the filtered underlying continuous image. As before, we use an object-space octree to cull hidden geometry rapidly. However, instead of using an image-space depth pyramid to test visibility of collections of pixel samples, we use a quadtree data structure to test visibility throughout image-space regions. When regions are too complex, we use quadtree subdivision to simplify the geometry as in Warnock's algorithm. Subdivison stops when the algorithm can either analytically filter the required region or bound the convolution integral appropriately with interval methods. To the best of our knowledge, this is the first algorithm to antialias with guaranteed accuracy scenes consisting of hundreds of millions of polygons.

An ideal visibility algorithm should a) quickly reject most of the hidden geometry in a model and b) exploit the spatial and perhaps temporal coherence of the images being generated. Ray casting with spatial subdivision does well on criterion (a), but poorly on criterion (b). Traditional Z-buffer scan conversion does well on criterion (b), but poorly on criterion (a). Here we present a hierarchical Z-buffer scan-conversion algorithm that does well on both criteria. The method uses two hierarchical data structures, an object-space octree and an image-space Z pyramid, to accelerate scan conversion. The two hierarchical data structures make it possible to reject hidden geometry very rapidly while rendering visible geometry with the speed of scan conversion. For animation, the algorithm is also able to exploit temporal coherence. The method is well suited to models with high depth complexity, achieving orders of magnitude acceleration in some cases compared to ordinary Z-buffer scan conversion.

We describe an efficient method for constructing a smooth surface that interpolates the vertices of a mesh of arbitrary topological type. Normal vectors can also be interpolated at an arbitrary subset of the vertices. The method improves on existing interpolation techniques in that it is fast, robust and general. Our approach is to compute a control mesh whose Catmull-Clark subdivision surface interpolates the given data and minimizes a smoothness or "fairness" measure of the surface. Following Celniker and Gossard, the norm we use is based on a linear combination of thin-plate and membrane energies. Even though Catmull-Clark surfaces do not possess closed-form parametrizations, we show that the relevant properties of the surfaces can be computed efficiently and without approximation. In particular, we show that (1) simple, exact interpolation conditions can be derived, and (2) the fairness norm and its derivatives can be computed exactly, without resort to numerical integration.

Article Free Access Share on CONDOR: constraint-based dataflow Author: Michael Kass Apple Computer, Advanced Technology Group, 20525 Mariani Ave., Cupertino, CA Apple Computer, Advanced Technology Group, 20525 Mariani Ave., Cupertino, CAView Profile Authors Info & Claims SIGGRAPH '92: Proceedings of the 19th annual conference on Computer graphics and interactive techniquesJuly 1992 Pages 321–330https://doi.org/10.1145/133994.134087Online:01 July 1992Publication History 36citation681DownloadsMetricsTotal Citations36Total Downloads681Last 12 Months9Last 6 weeks4 Get Citation AlertsNew Citation Alert added!This alert has been successfully added and will be sent to:You will be notified whenever a record that you have chosen has been cited.To manage your alert preferences, click on the button below.Manage my AlertsNew Citation Alert!Please log in to your account Save to BinderSave to BinderCreate a New BinderNameCancelCreateExport CitationPublisher SiteeReaderPDF

We present a method for texture synthesisbased on the simulation of a process of local nonlinear interaction, called reaction-diffusion, which has been proposed as a model of biological pattern formation. We extend traditional reaction-diffusion systems by allowing anisotropic and spatially non-uniform diffusion, as well as multiple competing directions of diffusion. We adapt reaction-diffusion systems to the needs of computer graphics by presenting a method to synthesize patterns which compensate for the effects of non-uniform surface parameterization. Finally, we develop efficient algorithms for simulating reactiondiffusion systems and display a collection of resulting textures using standard texture- and displacement-mapping techniques. 1 Introduction Texture mapping techniques have become so highly developed and so widely used that textureless images tend to appear barren, unrealistic, and boring. To date, though, techniques for synthesizing natural textures have advanced far les...

We present a new method for animating water based on a simple, rapid and stable solution of a set of partial differential equations resulting from an approximation to the shallow water equations. The approximation gives rise to a version of the wave equation on a height-field where the wave velocity is proportional to the square root of the depth of the water. The resulting wave equation is then solved with an alternating-direction implicit method on a uniform finite-difference grid. The computational work required for an iteration consists mainly of solving a simple tridiagonal linear system for each row and column of the height field. A single iteration per frame suffices in most cases for convincing animation.Like previous computer-graphics models of wave motion, the new method can generate the effects of wave refraction with depth. Unlike previous models, it also handles wave reflections, net transport of water and boundary conditions with changing topology. As a consequence, the model is suitable for animating phenomena such as flowing rivers, raindrops hitting surfaces and waves in a fish tank as well as the classic phenomenon of waves lapping on a beach. The height-field representation prevents it from easily simulating phenomena such as breaking waves, except perhaps in combination with particle-based fluid models. The water is rendered using a form of caustic shading which simulates the refraction of illuminating rays at the water surface. A wetness map is also used to compute the wetting and drying of sand as the water passes over it.

Spacetime constraints are a new method for creating character animation. The animator specifies what the character has to do, for instance, "jump from here to there, clearing a hurdle in between;" how the motion should be performed, for instance "don't waste energy," or "come down hard enough to splatter whatever you land on;" the character's physical structure---the geometry, mass, connectivity, etc. of the parts; and the physical resources' available to the character to accomplish the motion, for instance the character's muscles, a floor to push off from, etc. The requirements contained in this description, together with Newton's laws, comprise a problem of constrained optimization. The solution to this problem is a physically valid motion satisfying the "what" constraints and optimizing the "how" criteria. We present as examples a Luxo lamp performing a variety of coordinated motions. These realistic motions conform to such principles of traditional animation as anticipation, squash-and-stretch, follow-through, and timing.