Showing papers in "Informatica Didactica in 1990"

Snap-dragging in three dimensions.

Abstract: A large portion of the user interface in interactive solid modeling systems is devoted to the problem of placing and orienting objects in three dimensions. In particular, many operations must be provided for selecting control points, curves and surfaces, and for translating, rotating and scaling scene components into precise relationships with other scene components. By factoring these operations carefully, it is possible to provide the desired functionality so as to reduce both the size of the user interface and the time that it takes to use it. With snap-dragging, the user takes advantage of three main elements that work together: a general-purpose gravity function, alignment objects that can be created many at a time, and smooth-motion affine transformations. Scene composition is achieved in a single perspective view using a mouse and keyboard. With 19 mouse commands, 15 keyboard commands, 5 menus of numbers, and 1 single-level menu of numerical transformations, this user interface has fewer commands and requires fewer keystrokes than the skitters and jacks technique reported earlier.

Interactive real-time articulated figure manipulation using multiple kinematic constraints.

Abstract: In this paper, we describe an interactive system for positioning articulated figures which uses a 3D direct manipulation technique to provide input to an inverse kinematics algorithm running in real time. The system allows the user to manipulate highly articulated figures, such as human figure models, by interactively dragging 3D "reach goals." The user may also define multiple "reach constraints" which are enforced during the manipulation. The 3D direct manipulation interface provides a good mechanism for control of the inverse kinematics algorithm and helps it to overcome problems with redundancies and singularities which occur with figures of many degrees of freedom. We use an adaptive technique for evaluating the constraints which allows us to ensure that only a certain user-controllable amount of time will be consumed by the inverse kinematics algorithm at each iteration of the manipulation process. This technique is also sensitive to the time it takes to redraw the screen, so it prevents the frame display rate of the direct manipulation from become too slow for interactive control.

Acceleration techniques for progressive refinement radiosity.

Abstract: The progressive refinement radiosity method provides a means for computing the global illumination of an environment in time proportional to the size of the environment. Additionally, the method supplies a sequence of solutions that monotonically converge to a high-quality result, allowing it to be used for interactive applications that deliver "near real-time" updates as the computation proceeds. This paper presents two methods for accelerating the radiosity method. First, the traditional hemi-cube algorithm is modified to accelerate the expensive form-factor calculation. Second, the radiosity method is parallelized across a coarse-grain network, and the efficiency of the parallel system is discussed.

Physical modeling with B-spline surfaces for interactive design and animation.

Abstract: Physically based modeling has recently become a subject of widespread interest. This paper defines a model of elastic and plastic B-spline surfaces which supports both animation and design operations, including the interference detection, within the "Eplastics"/Alpha_1 modeling environment. We develop "refinement" operations for spring and hinge B-spline models which are compatible with the physics and the mathematics of B-spline models, including refinement. It is also a step towards a more continuous physical representation of a physical model than the more standard discretized geometry point mass models. We present some interactive operations currently in real-time and some which could be real-time with further optimization and use of multiple processors on machines such as the SGI Iris 4D/240GTX. A movie is used to illustrate the results.

Visualization methods and simulation steering for a 3D turbulence model of Lake Erie.

Abstract: A computational model of Lake Erie serves as a framework for a study of visualization techniques and display methods. Various display methods are used to examine the 3D data. The methods use primitive representations of polygons, volumes, lines and particles. The display methods also incorporate stereo imagery and animation. Three techniques of integrating the control of the computationl model and the display of images are discussed. These visualization techniques are post-processing, tracking and steering. A distributed software environment is used which implements these visualization techniques and display methods. The technique of steering is emphasized with a description of the software requirements and examples. A significant increase in productivity and comprehension is shown when steering is used.

The ThingWorld modeling system: virtual sculpting by modal forces.

Abstract: We describe a real-time solid modeling system that is based on the physical analogy of forming clay by applying forces. The system is implemented by simulating real materials as they react to user-supplied forces. Unlike other physically-based modeling approaches, the Thingworld system allows the user to restrict forming action to simple global deformations during the initial \"roughing in\" phase of modeling, and then later concern themselves with detailing. The Thingworld system also allows users to automatically model existing objects by using measurements taken from the object's surface. These measurements are used to generate artificial forces that mold the computer model much as a human would mold a clay model. Timed examples for constructing solid models are shown.

T-buffer: fast visualization of relativistic effects in space-time.

Abstract: We have developed an innovative ray-tracing simulation algorithm to describe Relativistic Effects in SpaceTime ("REST"). Our algorithm, called REST-frame, models light rays that have assumed infinite speed in conventional ray-tracing to have a finite speed in spacetime, and uses the non-Newtonian Lorentz Transformation to relate measurements of a single event in different inertial coordinate systems (inertial frames). Our earlier work [5][6][7] explored the power of REST-frame as an experimentation tool to study the rich visual properties in natural world modeled by Special Relativity. Non-intuitive images of the anisotropic deformation ("warping") of space, the intensity concentration/spreading of light sources in spacetime, and the relativistic Doppler shift were visualized from our simulations.

Real time spline curves from interactively sketched data.

Abstract: Hand-sketching is a particularly attractive solution to providing an intuitive design interface for modeling. The goal is to reduce the data collected from the input strokes and to construct a curve that faithfully represents the sketched data. This paper presents a new approach to interactive realtime handsketching in two or three dimensions and is-based on the new approach to general spline datafitting presented in [10,8,9].The goal of our approach is to obtain approximating curves with reasonable accuracy at real-time interactive speeds, and at the same time significantly reduce in the number of coefficients for the curve representation over the original data representation. The approach taken here to obtain realtime interaction is to reduce the data incrementally using new local algorithms while the data is still being sketched.

Rational hypersurface display.

Abstract: Algorithms are presented for polygonalizing implicitly defined, quadric and cubic hypersurfaces in n ≥ 3 dimensional space and furthermore displaying their projections in 3D. The method relies on initially constructing the rational parametric equations of the implicitly defined hypersurfaces, and then polygonalizing these hypersurfaces by an adaptive generalized curvature dependent scheme. The number of hyperpolygons used are optimal, in that they are the order of the minimum number required for a smooth Gouraud like shading of the hypersurfaces. Such hypersurface projection displays should prove useful in scientific visualization applications. The curvature dependent polygonal meshes produced, should also prove very useful in finite difference and finite element analysis programs for multi-dimensional domains.

The virtual erector set: dynamic simulation with linear recursive constraint propagation.

Abstract: We have implemented an algorithm for rigid body dynamics which unifies the advantages of linear recursive algorithms with the advantages of earlier linear algebra based constraint force approaches. No restriction is placed on the joints between links. The algorithm is numerically robust and can deal with arbitrary trees of bodies, including kinematic loops. Motion as well as force constraints on the dynamic behavior of any member of the linkage can be added easily. Through the use of spatial algebra notation---including our extension to account for spatial position---the mathematical expressions are simplified and more efficient to execute. The algorithm has been implemented on workstation class machines and performs at interactive speeds.

Towards image realism with interactive update rates in complex virtual building environments.

Abstract: Two strategies, pre-computation before display and adaptive refinement during display, are used to combine interactivity with high image quality in a virtual building simulation. Pre-computation is used in two ways. The hidden-surface problem is partially solved by automatically pre-computing potentially visible sets of the model for sets of related viewpoints. Rendering only the potentially visible subset associated with the current viewpoint, rather than the entire model, produces significant speedups on real building models. Solutions for the radiosity lighting model are pre-computed for up to twenty different sets of lights. Linear combinations of these solutions can be manipulated in real time. We use adaptive refinement to trade image realism for interactivity as the situation requires. When the user is stationary we replace a coarse model using few polygons with a more detailed model. Image-level linear interpolation smooths the transition between differing levels of image realism.

Distributing display lists on a multicomputer.

Abstract: We have developed techniques for distributing a hierarchical display list from a PHIGS-like library across a multicomputer. By storing a portion of the database at each processor, inter-processor communication is reduced. This reduction promises traversal of the display list at rates supporting rendering speeds of one million polygons/second or more, as we hope to achieve on our new machine, Pixel-Planes 5 (under construction). Our distribution techniques support order-dependent primitives and allow general display list editing.

Feeling and seeing: issues in force display.

Abstract: Force display technology works by using mechanica l actuators to apply forces to the user, By simulating th e physics of the user's virtual world, we compute these forces in real-time, then send them to the actuators so that the user feels them, The force display technology we use in th e Sandpaper system is a motor-driven two-degree of freedo m joystick (built by Max Behensky and Doug Milliken) . The joystick position is reported to the software, whic h computes the appropriate forces for the joystick's motors .

Interactive techniques for implicit modeling.

Abstract: Recent research has demonstrated the usefulness of implicit surfaces for modeling geometric objects. The interactive design of such surfaces has not, however, received the same attention as has the design of parametric surfaces. Principally this is due to the difficulty of controlling the shape of implicit surfaces while displaying the changes quickly enough for use within an interactive design environment. This paper describes progress towards interactive control of implicit surfaces and introduces new techniques useful to the designer.

Real-time digital of virtual acoustic environments.

Abstract: As with most research in information displays, virtual displays have generally emphasized visual information. Many investigators, however, have pointed out the importance of the auditory system as an information channel. We believe that a three-dimensional auditory display can substantially enhance situational awareness by combining spatial and semantic information to form dynamic, multidimensional patterns of acoustic events which convey meaning about objects in the spatial world of the user. Such a display can be realized with an array of real sound sources or loudspeakers (Doll et. al., 1986). The signal-processing device being developed at NASA-Ames maximizes flexibility and portability by synthetically generating three-dimensional sound in realtime for delivery through headphones. Unlike conventional stereo, sources can be perceived outside the head at discrete distances and directions from the listener. The 3-D auditory display is currently being integrated with Ames' Virtual Interactive Environment Workstation (VIEW) which allows the user to explore and interact with a 360-degree synthesized or remotely-sensed world using a head-mounted, wide-angle, stereoscopic display controlled by operator position, voice, and gesture.Applications of a three-dimensional auditory display involve any context in which the user's spatial awareness is important, particularly when visual cues are limited or absent. Examples include advanced teleconferencing environments, monitoring telerobotic activities in hazardous situations, and scientific "visualization" of multi-dimensional data. (e.g., Doll, et. al., 1986; Foley, 1987; Fisher, et. al., 1988; Brooks, 1988).

Reality built for two: a virtual reality tool.

Abstract: Researchers have been working with head mounted displays and virtual reality (VR) since 1965 when Ivan Sutherland published his first paper on the subject1. This work has centered on a single user within virtual space. The literature has covered applications such as telerobotics, virtual control panels, architectural simulation and scientific visualization.Several factors now militate toward broadening the range of VR applications: developments in hardware and software, as well as a growing readiness in many fields to incorporate VR. User interface constraints of VR systems need to change in response to this changing user profile. Design of environments and behaviors in virtual worlds should be simple and accessible to experts in many fields. With the advent of multi-user systems, communications will become a major application of virtual reality.VPL has recently developed a system that allows more than one user to share a virtual space. The forms and behaviors of virtual worlds are specified graphically, so that non-programmers can design them. The system, called Reality Built for Two, will be demonstrated at the Symposium on Interactive 3D Graphics.

Visualizing n -dimensional virtual worlds with n -vision.

Abstract: There are many applications in science, mathematics , statistics, and business, in which it is important to explore an d manipulate clam in more than three dimensions . In thes e applications, data can be defined by points in Euclidean n-space . A point's position is then specified with it coordinates . each o f which determines its position relative to one of It mutuall y perpendicular axes . We describe here research that has as its goa l the development of interaction techniques and metaphors for th e 4D and higher-dimensional worlds that this data represents .

A viewer for mathematical structures and surfaces in 3D.

Abstract: Salem is a viewer for exploring mathematica l structures and surfaces . Just as the Unix shell deal s mainly with text commands, files, and processes, ou r viewer deals with text and mouse commands, recursive geometric objects, views, and clients . Thu s clients can create and animate geometry with being concerned with programming to process commands and maintain views . Thus all clients share common models of graphics programming and user interaction as presented by the viewer, The viewer design i s flexible, so that even novice graphics programmers can add new applications or override the default rules ,

El lenguaje del cómic.

Abstract: Si superficialmente analizamos un Comic, descubrimos un objeto bidimensional con imagenes estaticas y textos, que en principio solo parece dar satisfaccion visual. Ahora bien, es mucho mas que eso: bello panorama de dibujos, grafismos o juego de colores, porque mediante el prodigioso fenomeno sinestesico, el cerebro humano interpreta los mensajes iconico-visuales como recibidos por otros umbrales sensitivos: gusto, tacto, olfato u oido. Y lo hace con tal eficiencia que el lector de imagenes puede vivir el tema ofrecido como historieta con todo tipo de transferencias de sensaciones. suenos y fantasias. Por lo tanto, si el Comic puede dar una riquisima informacion, es porque posee una estructura poderosa cuya singularidad es manifiesta.

A real-time optical 3D tracker for head-mounted display systems.

Abstract: In this paper, a new optical system for real-time, three-dimensional position tracking is described. This system adopts an "inside-out" tracking paradigm. The working environment is a room where the ceiling is lined with a regular pattern of infrared LEDs flashing under the system's control. Three cameras are mounted on a helmet which the user wears. Each camera uses a lateral effect photodiode as the recording surface. The 2D positions of the LED images inside the field of view of the cameras are detected and reported in real time. The measured 2D image positions and the known 3D positions of the LEDs are used to compute the position and orientation of the camera assembly in space.We have designed an iterative algorithm to estimate the 3D position of the camera assembly in space. The algorithm is a generalized version of the Church's method, and allows for multiple cameras with nonconvergent nodal points. Several equations are formulated to predict the system's error analytically. The requirements of accuracy, speed, adequate working volume, light weight and small size of the tracker are also addressed.A prototype was designed and built to demonstrate the integration and coordination of all essential components of the new tracker. This prototype uses off-the-shelf components and can be easily duplicated. Our results indicate that the new system significantly out-performs other existing systems. The new tracker provides more than 200 updates per second, registers 0.1-degree rotational movements and 2-millimeter translational movements, and processes a working volume about 1,000 ft3 (10 ft on each side).

Improving interaction with radiosity-based lighting simulation programs.

Abstract: We describe the main algorithms used in an interactive lighting simulation program based on a two-pass extension of the radiosity method. The system allows interactive walk-through as other systems based on radiosity calculations. Moreover, it offers increased realism in the lighting effects by use of extended form factors which accounts for "specular reflection of diffuse light", fast production and display of progressively refined images by distribution of the calculations, good quality of the images in the early stages of the refinement by the use of "hardware light sources", "cheap" rendering of some of the specular highlights at any time by use of the built-in specular shading model, lighting modification (color, intensity of the light sources) by use of "negative light", fast simulation of mirror effects and interactive tools for controling the quality of the final image.

Design for interactive performance in a virtual laboratory.

Abstract: In recent years, a number of research groups have implemented various versions of virtual world concept [2, 4, 6, 7]. A common thread among these virtual worlds is a direct manipulation user interface paradigm based on a glove device with the position and orientation of the hand registered by a tracking device. To explore this paradigm, a new project at IBM Research was started in 1989 to build a virtual laboratory for scientists and engineers. Our first step is to integrate the glove and space tracking devices with the real time graphics on a graphics superworkstation. A simple bouncing ball virtual world has been created to test underlying software and fine tune interactive performance.Our initial emphasis is placed on understanding the limitations of various system components and getting the best interactive performance from the system. With current state of technology, the glove and tracking devices can generate much more data than the graphics update process can utilize. Both the rendering process and the processes handling the device serial ports are CPU intensive. Our first design problem is how to distribute the processing and match the incoming data rates of input devices with the update rate of the graphics. After a new position from the tracker is received by the graphics, it is displayed only at the next frame update time giving the appearance that the hand image always lags behind the motion of the real hand. Our second design problem is to use techniques to compensate for this inherent lag time. This abstract describes the specific approaches we use to solve these problems and some useful insight gained in experimenting with lag time reduction by position prediction.