Carlo H. Séquin

Adaptive display algorithm for interactive frame rates during visualization of complex virtual environments

We describe an adaptive display algorithm for interactive frame rates during visualization of very complex virtual environments. The algorithm relies upon a hierarchical model representation in which objects are described at multiple levels of detail and can be drawn with various rendering algorithms. The idea behind the algorithm is to adjust image quality adaptively to maintain a uniform, user-specified target frame rate. We perform a constrained optimization to choose a level of detail and rendering algorithm for each potentially visible object in order to generate the “best” image possible within the target frame time. Tests show that the algorithm generates more uniform frame rates than other previously described detail elision algorithms with little noticeable difference in image quality during visualization of complex models. CR

Moving objects in space: exploiting proprioception in virtual-environment interaction

Manipulation in immersive virtual environments is difficult partly because users must do without the haptic contact with real objects they rely on in the real world to orient themselves and their manipulanda. To compensate for this lack, we propose exploiting the one real object every user has in a virtual environment, his body. We present a unified framework for virtual-environment interaction based on proprioception, a persons sense of the position and orientation of his body and limbs. We describe three forms of body-relative interaction: • Direct manipulation—ways to use body sense to help control manipulation • Physical mnemonics—ways to store/recall information relative to the body • Gestural actions—ways to use body-relative actions to issue commands Automatic scaling is a way to bring objects instantly within reach so that users can manipulate them using proprioceptive cues. Several novel virtual interaction techniques based upon automatic scaling and our proposed framework of proprioception allow a user to interact with a virtual world intuitively, efficiently, precisely, and lazily. We report the results of both informal user trials and formal user studies of the usability of the body-relative interaction techniques presented. CR

Visibility preprocessing for interactive walkthroughs

The number of polygons comprising interesting architectural models is many more than can be rendered at interactive frame rates. However, due to occlusion by opaque surfaces (e.g., walls), only a small fraction of a typical model is visible from most viewpoints.We describe a method of visibility preprocessing that is efficient and effective for axis-aligned or axial architectural models. A model is subdivided into rectangular cells whose boundaries coincide with major opaque surfaces. Non-opaque portals are identified on cell boundaries, and used to form an adjacency graph connecting the cells of the subdivision. Next, the cell-to-cell visibility is computed for each cell of the subdivision, by linking pairs of cells between which unobstructed sightlines exist.During an interactive walkthrough phase, an observer with a known position and view cone moves through the model. At each frame, the cell containing the observer is identified, and the contents of potentially visible cells are retrieved from storage. The set of potentially visible cells is further reduced by culling it against the observers view cone, producing the eye-to-cell visibility. The contents of the remaining visible cells are then sent to a graphics pipeline for hidden-surface removal and rendering.Tests on moderately complex 2-D and 3-D axial models reveal substantially reduced rendering loads.

OPASYN: a compiler for CMOS operational amplifiers

A silicon compilation system for CMOS operational amplifiers (OPASYN) is discussed. The synthesis system takes as inputs system-level specifications, fabrication-dependent technology parameters, and geometric layout rules. It produces a design-rule-correct compact layout of an optimized operational amplifier. The synthesis proceeds in three stages: (1) heuristic selection of a suitable circuit topology; (2) parametric circuit optimization based on analytic models; and (3) mask geometry construction using a macro cell layout style. The synthesis process is fast enough for the program to be used interactively at the system design level by system designers who are inexperienced in operational amplifier design. >

RISC I: a reduced instruction set VLSI computer

The Reduced Instruction Set Computer (RISC) Project investigates an alternative to the general trend toward computers with increasingly complex instruction sets: With a proper set of instructions and a corresponding architectural design, a machine with a high effective throughput can be achieved. The simplicity of the instruction set and addressing modes allows most instructions to execute in a single machine cycle, and the simplicity of each instruction guarantees a short cycle time. In addition, such a machine should have a much shorter design time. This paper presents the architecture of RISC I and its novel hardware support scheme for procedure call/return. Overlapping sets of register banks that can pass parameters directly to subroutines are largely responsible for the excellent performance of RISC I. Static and dynamic comparisons between this new architecture and more traditional machines are given. Although instructions are simpler, the average length of programs was found not to exceed programs for DEC VAX 11 by more than a factor of 2. Preliminary benchmarks demonstrate the performance advantages of RISC. It appears possible to build a single chip computer faster than VAX 11/780.

Management of large amounts of data in interactive building walkthroughs

Management of Large Amounts of Data in Interactive Building Walkthroughs Thomas A. Funkhouser, Carlo H. !Zquin and Seth J. Teller University of California at Berkeley* We describe techniques for managing large amounts of data during an interactive walkthrough of an architectural model. These techniques are based on a spatial subdivision, visibility analysis, and a display database containing objects described at multiple levels of detail. In each frame of the walkthrough, we compute a set of objects to render, i.e. those potentially visible from the observer’s viewpoint, and a set of objects to swap into memory, i.e. those that might become visible in the near future. We choose an appropriate level of detail at which to store and to render each object, possibly using very simple representations for objects that appear small to the observer, thereby saving space and time. Using these techniques, we cull away large portions of the model that are irrelevant from the observer’s viewpoint, and thereby achieve interactive frame rates. CR

Optimal adaptive k-means algorithm with dynamic adjustment of learning rate

Adaptive k-means clustering algorithms have been used in several artificial neural network architectures, such as radial basis function networks or feature-map classifiers, for a competitive partitioning of the input domain. The authors present a modification of the traditional k-means algorithm. This approach approximates an optimal clustering solution with an adaptive learning rate, which renders it usable even in situations where the statistics of the problem task slowly vary with time. Simulations comparing this improved adaptive k-means algorithm with other k-means variants are presented.<<ETX>>

Object associations: a simple and practical approach to virtual 3D manipulation

This paper describes a software framework to aid in designing and implementing convenient manipulation behaviors for objects in a 3D virtual environment. A combination of almost realistic-looking pseudo-physical behavior and idealized goal-oriented properties, called object associations, is used to disambiguate the mapping of the 2D cursor motion on the display screen into an appropriate object motion in the 3D virtual world and to determine a valid and desirable final location for the objects to be placed. Objects selected for relocation actively look for nearby objects to associate and align themselves with; an automated implicit grouping mechanism also falls out from this process. Concept, structure, and our implementation of such an object association framework in the context of the Berkeley Soda Hall WALKTHRU environment are presented.

Developable Bézier patches: properties and design

Geometric design of quadratic and cubic developable Bezier patches from two boundary curves is studied in this paper. The conditions for developability are derived geometrically from the de Casteljau algorithm and expressed as a set of equations that must be fulfilled by the Bezier control points. This set of equations allows us to infer important properties of developable Bezier patches that provide useful parameters and simplify the solution process for the patch design. With one boundary curve freely specified, five more degrees of freedom are available for a second boundary curve of the same degree. Various methods are introduced that fully utilize these five degrees of freedom for the design of general quadratic and cubic developable Bezier patches in 3D space. A more restricted generalized conical model or cylindrical model provides simple solutions for higher-order developable patches.

Fault tolerance in artificial neural networks

Different strategies for overcoming hardware failures in artificial neural networks are presented. The failure of one or more units in the hidden layer of layered feedforward networks is especially addressed. Different types of retraining techniques are investigated, and required retraining efforts are correlated with the internal representations for specific classification tasks. Subsequently, a practical technique is introduced to achieve true fault tolerance, i.e., to have the network continue to function correctly after failure of one or more hidden units. To achieve this fault-tolerant behavior, hidden units are randomly disabled for some pattern presentations during a standard backpropagation training phase. Prolonged training in this mode can achieve fault tolerance even with respect to fault patterns for which the network is not specifically trained