Eugene Fiume

Wires: a geometric deformation technique

Finding effective interactive deformation techniques for complex geometric objects continues to be a challenging problem in modeling and animation. We present an approach that is inspired by armatures used by sculptors, in which wire curves give definition to an object and shape its deformable features. We also introduce domain curves that define the domain of deformation about an object. A wire together with a collection of domain curves provide a new basis for an implicit modeling primitive. Wires directly reflect object geometry, and as such they provide a coarse geometric representation of an object that can be created through sketching. Furthermore, the aggregate deformation from several wires is easy to define. We show that a single wire is an appealing direct manipulation deformation technique; we demonstrate that the combination of wires and domain curves provide a new way to outline the shape of an implicit volume in space; and we describe techniques for the aggregation of deformations resulting from multiple wires, domain curves and their interaction with each other and other deformation techniques. The power of our approach is illustrated using applications of animating figures with flexible articulations, modeling wrinkled surfaces and stitching geometry together.

Depicting fire and other gaseous phenomena using diffusion processes

Developing a visually convincing model of fire, smoke, and other gaseous phenomenais among the most difficult and attractive problems in computer graphics. We have created new methods of animating a wide range of gaseous phenomena, including the particularly subtle problem of modelling “wispy” smoke and steam, using far fewer primitives than before. One significant innovation is the reformulation and solution of the advection-diffusion equation for densities composed of “warped blobs”. These blobs more accurately model the distortions that gases undergo when advected by wind fields. We also introduce a simple model for the flame of a fire and its spread. Lastly, we present an efficient formulation and implementation of global illumination in the presence of gases and fire. Our models are specifically designed to permit a significant degree of user control over the evolution of gaseous phenomena.

Sensor-actuator networks

Sensor-actuator networks (SANs) are a new approach for the physically-based animation of objects. The user supplies the configuration of a mechanical system that has been augmented with simple sensors and actuators. It is then possible to automatically discover many possible modes of locomotion for the given object. The SANs providing the control for these modes of locomotion are simple in structure and produce robust control. A SAN consists of a small non-linear network of weighted connections between sensors and actuators. A stochastic procedure for finding and then improving suitable SANs is given. Ten different creatures controlled by this method are presented. CR Categorias: G.3 [Probabuity and Statistics]: Probabilistic Algorithms; 1.2.6 [Artificial Intelligence]: Learning, Robotics; 1.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism animation; 1.6.3 [Simulation and Modeling] Applications.

Turbulent wind fields for gaseous phenomena

The realistic depiction of smoke, steam, mist and water reacting to a turbulent field such as wind is an attractive and challenging problem. Its solution requires interlocking models for turbulent fields, gaseous flow, and realistic illumination. We present a model for turbulent wind flow having a deterministic component to specify large-scale behaviour, and a stochastic component to model turbulent small-scale behaviour. The small-scale component is generated using space-time Fourier synthesis. Turbulent wind fields can be superposed interactively to create subtle behaviour. An advection-diffusion model is used to animate particle-based gaseous phenomena embedded in a wind field, and we derive an efficient physically-basedillumination model for rendering the system. Because the number of particles can be quite large, we present a clustering algorithm for efficient animation and rendering. CR

Limit cycle control and its application to the animation of balancing and walking

Seemingly simple behaviors such as human walking are difficult to model because of their inherent instability. Kinematic animation techniques can freely ignore such intrinsically dynamic problems, but they therefore also miss modeling important motion characteristics. On the other hand, the effect of balancing can emerge in a physically-based animation, but it requires computing delicate control strategies. We propose an alternative method that adds closedloop feedback to open-loop periodic motions. We then apply our technique to create robust walking gaits for a fully-dynamic 19 degree-of-freedom human model. Important global characteristics such as direction, speed and stride rate can be controlled by changing the open-loop behavior alone or through simple control parameters, while continuing to employ the same local stabilization technique. Among other features, our dynamic “human” walking character is thus able to follow desired paths specified by the animator.

An efficient search algorithm for motion data using weighted PCA

Good motion data is costly to create. Such an expense often makes the reuse of motion data through transformation and retargetting a more attractive option than creating new motion from scratch. Reuse requires the ability to search automatically and efficiently a growing corpus of motion data, which remains a difficult open problem. We present a method for quickly searching long, unsegmented motion clips for subregions that most closely match a short query clip. Our search algorithm is based on a weighted PCA-based pose representation that allows for flexible and efficient pose-to-pose distance calculations. We present our pose representation and the details of the search algorithm. We evaluate the performance of a prototype search application using both synthetic and captured motion data. Using these results, we propose ways to improve the applications performance. The results inform a discussion of the algorithms good scalability characteristics.

A fast shadow algorithm for area light sources using backprojection

The fast identification of shadow regions due to area light sources is necessary for realistic rendering and for discontinuity meshing for global illumination. A new shadow-determination algorithm is presented that uses a data structure, called a backprojection, to represent the visible portion of a light source from any point in the scene. A complete discontinuity meshing algorithm is described for polyhedral scenes and area light sources, which includes an important class of light/geometry interactions that have not been implemented before. A fast incremental algorithm for computing backprojections is also described. The use of spatial subdivision, and heuristics based on computed statistics of typical scenes, results in efficient mesh and backprojection computation. Results of the implementation show that the use of the backprojection and discontinuity meshing permits accelerated high-quality rendering of shadows using both ray-casting and polygon-rendering with interpolants.

Interactive control for physically-based animation

We propose the use of interactive, user-in-the-loop techniques for controlling physically-based animated characters. With a suitably designed interface, the continuous and discrete input actions afforded by a standard mouse and keyboard allow for the creation of a broad range of motions. We apply our techniques to interactively control planar dynamic simulations of a bounding cat, a gymnastic desk lamp, and a human character capable of walking, running, climbing, and various gymnastic behaviors. The interactive control techniques allows a performers intuition and knowledge about motion planning to be readily exploited. Video games are the current target application of this work.

A parallel scan conversion algorithm with anti-aliasing for a general-purpose ultracomputer

Popular approaches to speeding up scan conversion often employ parallel processing. Recently, several special-purpose parallel architectures have been suggested. We propose an alternative to these systems: the general-purpose ultracomputer, a parallel processor with many autonomous processing elements and a shared memory. The “serial semantics/parallel execution” feature of this architecture is exploited in the formulation of a scan conversion algorithm. Hidden surfaces are removed using a single scanline, z-buffer algorithm. Since exact anti-aliasing is inherently slow, a novel parallel anti-aliasing algorithm is presented in which subpixel coverage by edges is approximated using a look-up table. The ultimate intensity of a pixel is the weighted sum of the intensity contribution of the closest edge, that of the “losing” edges, and that of the background. The algorithm is fast and accurate, it is attractive even in a serial environment, and it avoids several artifacts that commonly occur in animated sequences.

Helping hand: an anatomically accurate inverse dynamics solution for unconstrained hand motion

We present a realistic skeletal musculo-tendon model of the human hand and forearm. The model permits direct forward dynamics simulation, which accurately predicts hand and finger position given a set of muscle activations. We also present a solution to the inverse problem of determining an optimal set of muscle activations to achieve a given pose or motion; muscle fatigue, injury or atrophy can also be specified, yielding different control solutions that favour healthy muscle. As there can be many (or no) solutions to this inverse problem, we demonstrate how the space of possible solutions can be filtered to an optimal representative. Of particular note is the ability of our model to take a wide array of joint interdependence into account for both forward and inverse problems. Given kinematic postures, the model can be used to validate, predict or fill in missing motion and improve coarsely specified motion with anatomic fidelity. Lastly, we address the visualization and understanding of the dynamically changing and spatially compact musculature using various interaction techniques.