Short Presentations

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https://diglib.eg.org/handle/10.2312/225

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Piecewise Constant Conic Sections for Accelerated Volume Density Rendering
(Eurographics Association, 2001) Hougs, Roland B.; Day, A. M.
In order to accelerate the rendering of volumetric shadows, we propose a new technique which builds sets of conic volumes to approximate the shape of shadows in a participating medium. The novelty of our approach is notably the construction of the cone-sets, which are built with no knowledge of the underlying geometry of the scene. Instead, information collected during the construction of a global photon map is used to derive an estimate of the outline of the shadows in three dimensions. This information is then used in several different ways to speed up the rendering pass. The method shares many of the advantages proposed by photon maps such as viewpoint independence and decoupling from the geometry of the scene.
A Visualization System for the Clinical Evaluation of Cerebral Aneurysms from MRA Data
(Eurographics Association, 2001) Perrin, James S.; Lacey, A.; Laitt, R.; Jackson, A.; John, Nigel W.
This paper details a work-in-progress application under development as part of a clinical visualization project. The software has been designed to meet the specific needs of interventional neuro-radiologists evaluating the suitability of intracranial aneurysms for endovascular coiling and also when planning the procedure. Providing rapid (real-time) interaction with high resolution iso-surfaces derived from Time-of Flight (ToF) Magnetic Resonance Angiography (MRA) data will enable the clinician to quickly assess the ability of the aneurysm to accept a coil, with greater reliability than exisiting, 2D film techniques. Simulating the interface of the C-arm angiography system, used during the procedure, allows the clinician to evaluate various surgical strategies, potentially reducing procedure times and therefore patient radiation dosage. The first release of the software is currently under-going clinical evaluation.
Free-Form Deformation of Solid Models in CSR
(Eurographics Association, 2001) Hui, K. C.; Lai, C.F.
Existing free-form deformation (FFD) techniques deform an object by deforming the space enclosing the object. Points on the object are thus deformed relative to the undeformed space (or world space). The deformed object is visualized by sampling points on the object surfaces, or by approximating the object with a polyhedral model. This provides good visual effect for the deformed objects. However, the deformed solid is represented in terms of the lattice of the FFD and the undeformed solid. There is no precise explicit representation of the deformed object so that existing solid modeling techniques, such as Boolean operations, on the deformed object may not be applied. This paper is concerned with the techniques of applying free-form deformation on solid models represented by the Constructive Shell Representation (CSR). By applying free-form deformation on the surface points of the trunctets of a CSR object so that the vertices and the quadric patch polynomial of the trunctets are changed, the shape of the object can be modified. This technique can be used to deform globally smooth solid models or general solid models with sharp edges. The deformation can be applied either globally or locally. Techniques for the deformation are discussed in detail. Experiments are conducted and the results are also presented.
CORBA Visualization Platform
(Eurographics Association, 2001) Benoist, Thierry; Hewitt, W. T.; John, Nigel W.
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Parametric Motion Blending through Wavelet Analysis
(Eurographics Association, 2001) Ahmed, Amr; Mokhtarian, Farzin; Hilton, Adrian
This paper shows how multiresolution blending can be employed with time-warping for realistic parametric motion generation from pre-stored motion data. The goal is to allow the animator to define the desired motion using its natural parameters such as speed. Generation of a realistic motion is achieved using pre-stored captured animations. Analysis has been carried out to investigate the relationship between the walking speed and blending factor to remove the burden of trial and errors from the animator. As a result, realistic walking motion with the speed specified by the user can be generated. This desired speed should be between the minimum and maximum speeds of the available motion data. Analysis to generalise these results to other motions are in progress. Generating the desired motion for different scaled avatars is also discussed.
Complexity Reduction of Catmull-Clark/Loop Subdivision Surfaces
(Eurographics Association, 2001) Steenberg, Eskil
By applying a filter this algorithm can reduce the number of polygons generated by subdividing a mesh dynamically. This algorithm is designed especially for real-time engines where the geometrical complexity is critical. It also avoids edge cracks and is generally more efficient than a general-purpose polygon reduction algorithm.
Collision Detection for Continuously Deforming Bodies
(Eurographics Association, 2001) Larsson, Thomas; Akenine-Möller, Tomas
Fast and accurate collision detection between geometric bodies is essential in application areas like virtual reality, animation, simulation, games and robotics. In this work, we address the collision detection problem in applications where deformable bodies are used, which change their overall shape every time step of the simulation. We propose and evaluate suitable bounding volume trees for deforming bodies that can be pre-built and then updated very efficiently during simulation. Several heuristics for updating the trees due to deformations are compared to each other. By combining a top-down and a bottom-up update strategy into a hybrid tree update method, promising results were achieved. Experiments show that our approach is four to five times faster than a previously leading method.
Animation of Facial Expressions by Physical Modeling
(Eurographics Association, 2001) Zhang, Yu; Prakash, Edmond C.; Sung, Eric
In this paper, we propose a physically-based 3D dynamic facial model based on anatomical knowledge for realistic facial expression animation. The facial model incorporates a physically-based approximation to facial skin tissue and a set of anatomically-motivated facial muscle actuators. The tissue model has multilayered mass-spring structure which approximates different types of facial tissue. Two kinds of biphasic springs, structural springs and shear springs, are included in our model to simulate nonlinear elastic behavior of the skin. Facial muscle models are presented to emulate facial muscle contraction. In the muscle model, two factors, the muscle force scaling factor and muscle strength factor provide us macro and micro control of the muscle influence respectively. Based on the facial anatomy, these contractile muscles are inserted at anatomically correct position within the dynamic skin model. Lagrangian mechanics governs the dynamics, dictating the deformation of facial surface in response to muscle forces. The dynamic facial animation algorithm runs at interactive rate with continuous 3D display on a graphics workstation.
3dml: A Language for 3D Interaction Techniques
(Eurographics Association, 2001) Figueroa, Pablo; Green, Mark; Hoover, H. James
We present 3dml, a markup language for 3D interaction techniques and virtual environment applications that involve non-traditional devices. 3dml has two main purposes: readability and rapid development. Designers can read 3dml-based representations of 3D interaction techniques, compare them, and understand them. 3dml can also be used as a front end for any VR toolkit, so designerswithout programming skills can create VR applications as 3dml documents that plug together interaction techniques, VR objects, and devices. This paper focuses on the language features and presentation scheme designed in our website (http://www.cs.ualberta.ca/~pfiguero/3dml).
Approximated Phong Shading by using the Euler Method
(Eurographics Association, 2001) Hast, Anders; Barrera, Tony; Bengtsson, Ewert
After almost three decades and several improvements, Gouraud shading is still more often used for interactive computer graphics than Phong shading. One of the main reasons for this is of course that Phong shading is computationally more expensive. Quadratic polynomial approximation techniques like Bishop’s method could reduce the amount of computation in the inner loop to just the double of what is done in Gouraud shading. By using Euler’s method we get another quadratic polynomial approximation technique which is just as fast in the inner loop, but it will also give correct intensities on the edges, which we will not get with Bishop’s method. By computing the maximum difference over a scan line between Gouraud shading and the proposed method, we could decide if Gouraud will suffice. It is also shown that linearly interpolated normals are normalized by a symmetric function. This means that we could reduce the amount of square roots by the half in Phong shading.
Scalable Impressionist Rendering
(Eurographics Association, 2001) Atencia, A.; Bourdin, Jean-Jacques; Boyer, V.; Pissard, T.; Sobczyk, D.
The painted impressionist technique produces scale based effects: the far range vision is almost realistic while the close vision is blurred. In NPR, Impressionist Renderers are mainly based on a medium range vision. A very accurate scalable impressionist effect has been implemented and improves both close and far range vision.
Interactive 3D Modeling in the Inception Phase of Architectural Design
(Eurographics Association, 2001) de Vries, B.; Jessurun, A.J.; van Wijk, J.J.
In architectural design 3D modeling in the inception phase is up to now not supported in CAD. Moreover 3D modeling is still far from intuitive with the common interface techniques. This paper introduces a 3D modeling tool for architects, which is limited in its purposes but yet very powerful in its use. A cube is the basic drawing element to construct building masses. Modification of the design is achieved by dragging sets of cubes resulting in the creation or deletion of new cubes.
Post-rendering Composition for 3D Scenes
(Eurographics Association, 2001) Grimm, Cindy
In traditional art a painter displays a 3D scene on a 2D image plane in a manner that is aesthetically pleasing. The arrangement of objects and colors is called composition and is the subject of many art books and classes. While a painter may use perspective to create depth in a scene they may also alter the perspective and color, either subtly or dramatically, to influence the focus of viewer and the effect of the image. To date, traditional 3D graphics packages have largely concentrated on modeling, textures, and lighting to create images and provide few tools for altering the composition post-rendering. In this paper we present several simple techniques for creating images with non-standard perspective and color using standard 3D rendering packages. The scene is modeled in 3D but each object has its own camera, color balance, and image size, allowing the user to alter the composition after the 3D rendering step. The purpose of this paper is not to present a complete composition system but rather to illustrate the potential of compositionbased tools.
Automatic Animated Face Modeling Using Multiview Video
(Eurographics Association, 2001) Wu, Fu-Che; Murphy, Chien-Chang Ho; Ouhyoung, Ming
An image-based 3-D modeling system is presented in this paper. Our modeling system consists of three main stages: camera calibration, depth estimation and 3-D geometry reconstruction. All of these steps are executed automatically. In the camera calibration stage, some patterns are used that help to determine the camera’s position in an environment. The camera’s intrinsic and external parameters are determined using epipolar geometry. After the camera parameters are determined, the camera’s location in each projected frame is determined. The depth for each pixel in a base image is estimated from the camera’s focus to the object’s surface by measuring the similarity between the base image and the neighboring images. The object’s 3-D geometry is reconstructed with texture from the base image using the depth information.
Space-Time Hierarchical Radiosity with Clustering and Higher-OrderWavelets
(Eurographics Association, 2001) Damez, Cyrille; Holzschuch, Nicolas; Sillion, Francois X.
We address in this paper the issue of computing global illumination solutions for animation sequences. The principal difficulties lie in the computational complexity of global illumination, emphasized by the movement of objects and the large number of frames to compute, as well as the potential for creating temporal discontinuities in the illumination, a particularly dangerous and noticeable artifact. We demonstrate how space-time hierarchical radiosity, i.e. the application to the time dimension of a hierarchical decomposition algorithm, can be effectively used to obtain smooth animations: first by proposing the integration of spatial clustering in a space-time hierarchy; second, by changing the wavelet basis used for the temporal dimension. The resulting algorithm is capable of creating time-dependent radiosity solutions efficiently.
Animating cuts with on-the-fly re-meshing
(Eurographics Association, 2001) Ganovelli, Fabio; O’Sullivan, C.
The problem of defining a model for deformable objects which allows the user to perform cuts is still open. Generally speaking, the reason is that such a task affects the connectivity and the topology of the mesh, while the assumption that they never change is the basis of most algorithms for both computation of deformation and collision detection. The drawback of approaching this problem as one of cutting based on re-meshing, is that the mesh exhibits a higher density where it has been cut than elsewhere. This paper proposes an on-the-fly tetrahedral simplification scheme to cope with such a fragmentation problem.
HYPER MASK – Projecting a Virtual Face onto a Moving Real Object
(Eurographics Association, 2001) Morishima, Shigeo; Yotsukura, T.; Nielsen, F.; Binsted, K.; Pinhanez, C.
HYPERMASK is a system which projects an animated face onto a physical mask, worn by an actor. As the mask moves within a prescribed area, its position and orientation are detected by a camera, and the projected image changes with respect to the viewpoint of the audience. The lips of the projected face are automatically synthesized in real time with the voice of the actor, who also controls the facial expressions. As a theatrical tool, HYPERMASK enables a new style of storytelling. As a prototype system, we propose to put a self-contained HYPERMASK system in a trolley (disguised as a linen cart), so that it projects onto the mask worn by the actor pushing the trolley.
Artist Driven Expressive Graphics
(Eurographics Association, 2001) Mason, Kaye; Carpendale, Sheelagh
Current methods in non-photorealistic graphics can place a heavy emphasis on the algorithm, as opposed to the artist. In this paper, we analyse these trends, and present a conceptual framework for putting control back in the hands of the artist. Combining ideas from non-photorealistic graphics and artificial intelligence, we present new methods of supporting alternative artistic styles. Details of our implementation of this model are described, as well as methods for interaction. Finally, we create a simulation under this framework, and show preliminary results.
Individualising Human Animation Models
(Eurographics Association, 2001) Ju, Xiangyang; Siebert, J. Paul
Realistic human body animation requires accurate body geometry, realistic textures and believable behaviours. Existing human animation models provide excellent tools to control articulated motion and body surface deformations according to body postures, but modelling a specific individual requires a large degree of skill to sculpt a model resembling that individual. The advent of 3D imaging collection techniques means that the highly accurate 3D surface of a specific person can now be collected in a matter of milliseconds, but most captured 3D surfaces have little semantic information. Consequently, a significant degree of laborious manual intervention is still required to produce a virtual character from their 3D image using traditional animation approaches. The authors present a method for combining 3D images of real people with existing nonspecific, i.e. generic, human animation models to achieve highly realistic human animation models of the 3D imaged individuals. This has been achieved by developing a two-step method for conforming a generic human animation model to fit or “clone” the 3D geometry captured from a specific individual. A segmentation procedure is first applied to the 3D imaged human body surfaces to impose a semantic labelling of the data into body surface parts. Having thereby established correspondence between the segments of the scanned human body and those of the generic model, a rigid body transformation followed by a global 3D mapping is applied to bring the generic mesh into approximate alignment with the 3D imaged model. The second step comprises a conformation procedure driven by (minimising) the distance between the closestpoints between the respective meshes to bring the generic model surfaces into close alignment with those of the real-world 3D surfaces.
Managing Gigabyte Virtual EnvironmentWalkthrough
(Eurographics Association, 2001) Shou, Lidan; Chionh, Jason; Huang, Zhiyong; Ruan, Yixin; Tan, Kian-Lee
In this paper, we study the problem of interactive walkthrough of a large virtual environment (VE) where the data representing 3D virtual objects can not reside completely in the main memory. We tap into the wealth of techniques (indexing, caching, prefetching) that have been widely used by the database community, and investigate how walkthrough semantics can be integrated into these techniques. In our approach, the VE data in the main memory are dynamically managed such that only those of the relevant 3D objects pertaining to the current user’s viewpoint are loaded into the main memory. The objects in the VE are spatially indexed by a spatial index structure (R-tree) as opposed to splitting the VE into smaller rigid-sized grids. Queries are issued to the R-tree to retrieve only the relevant objects. We propose a novel complement search algorithm to improve the standard search. In addition, we propose a cache replacement policy that considers the access pattern of walkthrough to facilitate effective memory management; and a prediction algorithm that computes the next likely position of the user in order to prefetch data. We implemented a prototype walkthrough system and evaluated it on a 1 GB synthetic dataset of a cityscape. Our results show that the proposed techniques deployed can lead to a high constant frame rate for the walkthrough.

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