Showing papers in "IEEE Computer Graphics and Applications in 1987"

Automatic Creation of Object Hierarchies for Ray Tracing

Abstract: Intersection calculations dominate the run time of canonical ray tracers. A common algorithm to reduce the number of intersection tests required is the intersection of rays with a tree of extents, rather than the whole database of objects. A shortcoming of this method is that these trees are difficult to generate. Additionally, manually generated trees can be poor, greatly reducing the run-time improvement available. We present methods for evaluation of these trees in approximate number of intersection calculations required and for automatic generation of good trees. These methods run in O(nlogn) expected time where n is the number of objects in the scene. We report some examples of speedups.

Fourier Synthesis of Ocean Scenes

Abstract: Considerable interest in scene synthesis has focused on fractal techniques such as 1/f noise filtering. However, these techniques produce poor synthetic ocean scenes. A superior technique is presented here that used an empirical sea spectrum model to represent a fully developed sea in nautre. A computer program has been written whereby a user supplies a wind velocity, and a two-dimensional Fourier-domain filter is created whose shape is decribed by the modified Pierson-Moskowitz spectrum. A white-noise image can then be filtered and rendered with a ray-tracing algorithm to produce a realistic ocean scene. Wave motion may be invoked by manipulating teh phase of the Fourier-transormed white-noise image. Several phase-manipulating techniques have been implemented.

The Direction of Synthetic Actors in the Film Rendez-Vous a Montreal

Abstract: This article describes how the synthetic actors Marilyn Monroe and Humphrey Bogart were directed in the film Rendez-vous a Montreal, using the Human Factory software. Innovative points are emphasized. The recreation of famous persons and reconstitution of their personalities, as well as the corresponding animation, are considered from an artistic point of view. Technical points discussed are personalized expressions, abstract muscle action (AMA) procedures, expression key-frame interpolation, multitrack mixing and synchronization, automatic body mapping using joint-dependent local deformation (JLD) operators, and semi-automatic object grasping. Task-level problems are also explained. Finally, how a fifth-generation animation system might evolve is discussed.

Articulated Figure Positioning by Multiple Constraints

Abstract: A problem that arises in positioning an articulated figure is the solution of 3D joint positions (kinematics) when goal positions, rather than joint angles, are given. If more than one such goal is o be achived, tge problem is often solved interactively by positioning or solving one component of the linkage, then adjusting another, then redoing the first, and so on. This iterative process us skiw abd tedious. We present a method that automatically solves multiple simultaneous joint position goals. The user interface offers a six-degree-of-freedom input device to specify joint angles and goal positions interactively. Examplesare used to demonstrate the power and efficiency of this method for keypositon animation.

Experiences with the Alternate Reality Kit: An Example of the Tension between Literalism and Magic

Abstract: This article presents an overview of the Alternate Reality Kit, an animated environment for creating interactive simulations. ARK is built upon a physical-world metaphor: All objects have an image, a position, a velocity, and the ability to experience forces. Users manipulate objects with a mouse-operated "hand," which enables them to carry and throw objects, press buttons, and operate sliders. The interface features are discussed in light of a general user interface tension between literalism and magic. Literal features?defined as those that are true to the interface's metaphor?enhance an interface's learnability. Magical features are defined as those capabilities that deliberately violate the metaphor in order to provide enhanced functionality. Discussion of each ARK feature includes informal observations of early ARK users, and an assessment of the feature's learnability, its usefulness, and its position on the magical-literal axis. Despite ARK's magical features, applications-level users have been trained in a few minutes. Although this article is about ARK, the tension between literalism and magic raises some interesting questions on its own. Some of these questions are presented briefly in the conclusion.

Machine Understanding of CSG: Extraction and Unification of Manufacturing Features

Abstract: Constructive Solid Geomety (CSG)-albeit a concise, powerful, and informationally complete scheme-does not explicitly present certain high-level conceptual information, which is directly available from traditional engineering drawings and has been extremely useful for manufcturing processes. Such manufacturing fetures as chamfer, round, fillet, bore, and neck are typical examples of this kind of information. The fact that CSG is unambiguous but not unique, however, has posed great difficulties in the development of algorithms capable of understanding CSG and making it more useful for manufactuing. We propose a general apporach, based on principal axis and tree reconstruction, to extract and unify feature representations while retaining the simplicity and conciseness of CSG.

Using Dynamic Analysis for Realistic Animation of Articulated Bodies

Abstract: A major problem in computer animation is creating motion that appears natural and realistic, particularly in such complex articulated bodies as humans and other animals. At present, truly lifelike motion is produced mainly by copying recorded images, a tedious and lengthy process that requires considerable external equipment. An alternative is the use of dynamic analysis to predict realistic motion. Using dynamic motion control, bodies are treated as masses acting under the influence of external and internal forces and torques. Dynamic control is advantageous because motion is naturally restricted to physically realizable patterns, and many types of motion can be predicted automatically. Use of dynamics is computationally expensive and specifying controlling forces and torques can be difficult. However, there is evidence that dynamics offers hope for more realistic, natural, and automatic motion control. Because such motion simulates real world conditions, an animation system using dynamic analysis is also a useful tool in such related fields as robotics and biomechanics.

A Proposal for Standard Graphics Environments

Abstract: ray tracing, researchers continue to explore which is the fastest way to find the closest intersection point for a ray and a set of primitives. The problem faced by these and other people involved in computer graphics is a lack of standards. Within the hardware field there has been some progress in solving this problem. A frequently quoted number for a graphics accelerator is the number of polygons per second that can be output to the screen. A number of companies use the same standard, defining an

Interactive Design of 3D Computer-Animated Legged Animal Motion

Abstract: A visually interactive approach to the design of 3D computer-animated legged animal motion in the context of the PODA computer animation system is presented. The design process entails the interactive specification of parameters that drive a computational model for animal movement. The animator incrementally modifies a framework for establishing desired limb and body motion as well as the constraints imposed by physical dynamics (Newtonian mechanical properties) and temporal restrictions. PODA uses the desired motion and constraints specified by the animator to produce motion through an idealized model of the animal's adaptive dynamic control strategies.

Toward Automatic Motion Control

Abstract: Motion control for computer animation is a rich area for new research. The trend toward greater complexity in animation makes the development of more convenient and automatic methods of motion control important. Most commonly used motion control methods, such as keyframing and scripts, require a great deal of user effort to design acceptable animations. More automic methods will allow the production of sophisticated animation with less user effort. These methods include dynamic analysis, path planning and collision avoidance, stimulus-response control, and learning algorithms.

Free-Form Solid Modeling with Trimmed Surface Patches

Abstract: Solid modelers store a more complete representation than wireframe or surtace modelers. This completeness permits the automation of such tasks as interference analysis, mass property calculation, and finite element mesh generation. But the denser information content and complex algorithms needed to perform these tasks complicate the support of free-form geometry, especially Boolean operations. Consequently, the high degree of geometric coverage traditionally found in surface modeling systems has not, for the most part, been equaled in modern solid modelers. This article explores some of the difficulties encountered in Boolean combinations of free-from solids and presents a geometric representation designed to circumvent them.

A Control-Point-Based Sweeping Technique

Abstract: This article presents a general sweeping technique for nonuniform rational B-splines. This operator allows sweeps with several cross sections along a 3D path. One can scale the cross sections along the path according to the shape of a profile curve. The definition of the resulting surface is inherited from the initial curves, and you compute its control mesh from the control polygon of these curves. We shall consider several special cases, like straight lines and rational curves; characteristics of circles and straight lines are preserved.

Information Modeling

Abstract: Continuing the theme from the last column,1 this time I want to discuss information modeling in more detail. The central premise of the PDES/STEP exchange standardization effort is that the \"stuff\" to be exchanged is information, but during the actual exchange the information is represented by data. The data forms used can differ according to the target computer exchange technology. The objectives of PDES can be summarized as

Interactive Data Interpolation by Rational Bezier Curves

Abstract: Some interpolation techniques produce curves that the designer considers unsatisfactory. Even when the data points lie on an apparently simple curve, the resulting interpolant may not be the obvious one. This article presents an algorithm that combines interactive techniques with interpolation methods to allow user intervention. Rational Bezier curves are used as local interpolants, and an approach is discussed for exploiting shape parameters.

Creating Interaction Techniques by Demonstration

Abstract: When creating highly interactive, direct-manipulation interfaces, one of the most difficult design and implementation tasks is handling the mouse and other input devices. Peridot, a new user interface management system, addresses this problem by allowing the designer of the user interface to demonstrate how the input device should be handled by giving an example of the interface in action. The designer uses sample values for parameters, and the system automatically infers the general operation and creates the code. After an interaction is specified, it can be executed rapid prototyping, since it is very easy to design, implement, and modify mouse-based interfaces. Perudit also supports such additional input devices as touch tablets, as well as multiple input devices operating in parallel (for example, one in each hand) in a natural, easy-to-specify manner. All interaction techniques are implemented using active values, which are like variables except that the objects that depend on active values are updated immediately whenever they change. Active values are a straightforward and efficient mechanism for implementing dynamic interactions.

An Application of Computer Graphics and Networks to Anatomic Model and Prosthesis Manufacturing

Abstract: Computer graphics has now matured in medical applications from 2D and 3D presentations for diagnosis and the planning of surgery and therapy to become the key step in making hand-held models of custom prostheses. The system described here delivers 3D shape information to create skeletal models, plan corrective surgery, and directly manufacture prostheses. Implants and anatomic models are manufactured using computed tomography (CT) image data and a system to generate Instructions for numerically controlled machines. The system combines clinical imaging, an algorithm for 3D edge detection, computer communications, and computer-aided and manufacturing (CAD/CAM). This integration of technologies brings recent advances in computer-aided design and manufacturing to the local community CT scanning clinic in a cost-effective manner. Via computer communications, several hundred remote medical imaging centers can have their CT scanners connected on-line to CAD/CAM facilities that one could not support alone. Operators of the remote CT scanners bear only the cost of computer communications equipment to being their patients this service. We use the clinical course of several patients in whom prostheses have been implanted to describe this technology.

A Configurable Pixel Cache for Fast Image Generation

Abstract: This article describes an approach to fast image generation that uses a high-speed serial scan converter, a somewhat slower frame buffer, and a pixel cache to match the bandwidth between the two. Cache hit rates are improved by configuring the cache to buffer either 4 × 4 or 16 × 1 tiles of frame memory, depending on the type of operation being performed. For line drawing, the implenmention discribed can process 300,000 30-pixel vectors per second. For shaded polygons, the system can fill 16,000 900-pixel polygons per second. In addition to buffering pixel intensity data, the pixel cache also buffer z (depth) values, improving the performance of the z-buffer hidden-surface algorithm. By utilizing z-value caching, the system can process 5800 900-pixel shaded polygons per second with hidden-surface removed.

Infinite Control Points-A Method for Representing Surfaces of Revolution Using Boundary Data

Abstract: Methode pour representer les surfaces de revolution a partir d'elements de frontiere utilisant des points de controle infinis

A Generalized Scanning Technique for Display of Parametrically Defined Surfaces

Abstract: Special attention is given to the adaptation of the technique for efficiency to both polynomial and rational Bezier patches. The resulting algorithms are simple and robust. Their speed depends mainly on the surface area of the object being rendered, not on the number of surface patches. The technique is particularly suitable for rapid display of geometrically complex objects. Since the technique directly renders from the definitions of the surfaces without needing polygons, it can maintain a relatively compact database. Several examples with timing are included. The technique described creates smooth, shaded images for parametrically defined surfaces. It depends on a general surface scan to generate a dense set of points that represents the surface. Hidden surfaces are eliminated by sorting the sample points into a z-buffer and retaining the points nearest the viewer. Alternative schemes are given for computing the surface normal for each point in the z-buffer. Conventional illumination routines can then be applied to determine the intensities at each pixel, although the reflection-mapping technique is preferred for this article.

The Origins of the Teapot

Abstract: Are you interested in more articles of this type? Are you interested in data (such as the teapot data) or code or both? Do you have public domain data and/or code that you would be willing to share? Please send your answers and comments to chip Hatfield, Lawrence Livermore National Laboratory, PO Box 5504, L-156, Livermore, CA 94550 or HATFIELD@LLL-ICDC.ARPA.

Solid Texturing of Soft Objects

Abstract: Since the shape of a soft object changes in response to its surroundings, it is difficult to give a single position in space as the location of the object. Indeed objects can and do break dynamically into subobjects. This means that you cannot map a solid texture onto such an object simply by using a function of the space coordinates. We have taken a different approach. Our soft objects are modeled as the volume enclosed by an isosurf ace of a field calculated from a set of key points. For each key point, we describe an abstract texture space. Any point on the surface of an object has, associated with each key point, a position in this space and a field contribution. A vector sum of these positions, weighted by the field contributions, is used to select a surface specification from the texture space. Textures mapped with this process retain their consistency during distortion and metamorphoses of objects, permitting a great variety of animation effects.

Ambiguities in Incremental Line Rastering

Abstract: In implmenting rater grahic algorithms, it is impotant to toroughly understand behavior and implicit defaults inherent in each algorithm. Design choices must balance performance with respect to drawing speed, circult count, code space, picture fidelity, system complexity, and system consistency. For example, "close" may sound appealing when describing the match of the rastered representation to a geometirc line. An implementation, however, must quantily an error metric?such as minimum normal distance between candidate raster grid points and the geometric line?and resolve "ties" in which two candidate grid points have an equal error metric. Equal error metric ambiguity can permit algorithimic selection of raster points for a line from (X0, Y0) to (X1, Y1) to differ from points selected rastering the same line back from (X1, Y1) to (X0, Y0). Modilying a rastering algorithm to provide an exactly reversibie path, though, will cause problems when lines are rastered in a context of approximating a circle with a polygon. Only by fully understanding any algorithm can designers determine whether such pel-level anomalies are worth the code space or circuit count necessary to provide explicit user resolution, or whether a fixed default must suffice. This article discusses implementation considerations relevant to selecting and customizing incremental line-drawing algorithms to cope with such anomalies as equal error metric instances, perturbation effects of clipping, interesections in raster space, EXOR interpretations for polylines, reversibility, and fractional endpoint rounding.

Realism in Computer Graphics: A Survey

Abstract: This article surveys most of the major issues to be dealt with when generating realistic images, and covers papers up to December 1985. It begins with an overview of the rendering process and a quick review of visible-surface-determination algorithms. Then, in more detail, it discusses shading, antialiasing, texture mapping, shadows, and optical effects and closes witha discussion of modeling primitives.

An Algorithm for Geometric Set Operations Using Cellular Subdivision Techniques

Abstract: Geometric set operations play an integral role in systems for CAD/CAM, for robot planning, and for modeling objects such as underground formations from empirical data. Two major issues in the implementation of geometric set operations are efficiency in the search for geometric intersections and effectiveness in the treatment of singular intersection cases. This article presents an algorithm for geometric set operations on planar polyhedral nonmanifold objects that addresses both these issues. First, an efficient search for geometric intersections is obtained by localizing the search to small regions of object space through a cellular subdivision scheme using the polytree data structure. Second, an effective treatment of singular intersection cases is obtained by mapping each singular intersection occurring in a region into one of a small set of cases.

Digitizer Technology: Performance Characteristics and the Effects on the User Interface

Abstract: Tablet digitizers are common devices for getting graphical data into a computer. For many applications, they are the only practical device. Because tablet digitizers have been in existence for many years, they are often regarded as "old hat" technology?nothing new can be said about them and no significant technical developments other than price decreases can be expected. This is a misconception. We have found several misunderstood performance characteristic, characteristics that can have a major effect on the user's ability to use a tablet digitizer in many interactive applications. The risk to an application designer is that the or she may base the interface design on incorrect assumptions. As a consequence, the interface may be awkward to use. The article shows what some of these characteristics are how to evaluate their effect in different classes of applications. Specific examples are taken from a hand-printing application for character recognition.

C1 Quadratic Interpolation over Arbitrary Point Sets

Abstract: New formulas for generating smooth surfaces over arbitrarily spaced data points are developed The formulas are based on quadratic polynomials for the construction of derivative continuous surfaces rather than on the cubic polynomials generally used The technique is based on a subdivision procedure, dividing each triangle in a triangulation of the data points into six subtriangles and fitting a quadratic Bezier surface patch over each subtriangle THe formulas require only function and first derivative values at the data points and are easily evaluated in terms of the Bezier coefficients Since two-dimensional quadratic polynomials contain only six terms, while 10 terms are required to evaluate a cubic, the new procedure significantly improves the efficiency of algorithms for drawing surfaces in computer-aided geometric design

A Short History of CAD Data Transfer Standards

Abstract: Early Days I find it surprising that the first specifications for CAD data transfer were for solid modeling systems rather than drafting systems. The need to transfer data between drafting systems electronically was recognized in the early seventies by the ANSI Y14 Committee. A small voluntary effort was started to develop a standard for a transfer file format, and some drafts were produced. In the late seventies, although there were very few solid modelers outside the universities, the Geometric Modeling Project of CAM-I recognized the need to transfer the data between these types of systems as well as drafting systems. Accordingly , McDonnell Douglas Automation (McAuto) was commissioned to prepare a file specification for solid modeling data, based on the ideas in the ANSI working documents. This contract was duly completed in 19791 and covered both Constructive Solid Geometry (CSG) and Boundary Representation (B-rep) solid representations. Slightly later CAM-I also commissioned Shape Data Ltd. to develop a procedural iriterface for solid-modeling systems. This is known as the Application Interface Specification (AIS) and catered to both CSG and B-rep solids as well as simplified B-rep models that could be used for describing sheet metal parts and piping systems. This work was completed in 1980 but has since been extended and revised.2 Meanwhile, in parallel with the ANSI effort, a concentrated three-month industry effort under the auspices of the National Bureau of Standards put together the IGES

Fast Perspective Views of Images Using One-Dimensional Operations

Abstract: Generating arbitrary perspective views of images portraying 3D surfaces can involve extensive computation and data I/O time because of the problems in determining visibility, and performing hidden-point removal. Appropriate 1D transforms of an image can allow hidden-point removal and perspective projection to be performed on scan lines or columns of these transforms. Perspective view generation then reduces to a series of extremely fast 1D operations. As a result, exact perspective views of 3D surfaces of unlimited size can be generated very much more rapidly than hitherto possible, making this a feasible interactive tool in image analysis. Maximum speed is possible when entire data sets can be stored in random access memory (RAM). However, the scan-line nature of the algorithm also allows sequential processing of data stored on disk, and fast image transposition methods allow the generation of views of surfaces much larger than available memory.

How Many Ways Can You Draw a Circle

Abstract: This is the, first in a series of columns on whatever I want to say about Computer Graphics. I intend in this column to explore ideas of interest to me-primarily geometdic and algorithmic games pertaining to picture making-perhaps interspersed with my foaming at the mouth over philosophical issues about what-it-allmeans.1I have a bunch of ideas to start with, bbut as time goes on, 'I hope others will write in ideas and suggestions I can report on.

The Feasibility of a VLSI Chip for Ray Tracing Bicublic Patches

Abstract: In this article we explore the possibility of a VLSI chip for ray tracing bicubic patches in Bezier form. The purpose of the chip is to calculate the intersection point of a ray with the bicubic patch to a specified level of accuracy, returning parameter values (u,v) specifying the location of the intersection on the patch, and a parameter value, t, which specifies the location of the intersection on the ray. The intersection is calculated by succesively subdividing the patch and computing the intersection of the ray with a bounding box of each subpatch until the bounding volume meets theaccuracy requirement. There are two operating modes: another in which all intersections are found. This algorithm (and the chip) correctly handle the difficult cases of the ray tangentially intersecting a planar patch and intersections of the ray at a silhouette edge of the patch. Estimates indicate that such a chip could be implemented in 2-micron NMOS (N-type metal oxide semiconductor) and could computer patch-ray intersections at the rate of one every 15 microseconds for patces that are prescaled and specified to a 12-bit fixed point for each of the x, y, and z components. A version capable of handling 24-bit patches could compute patch/ray intersections at the rate of one every 140 section point could be performed with the addition of nine scalar subtractions and six scalar multiplies. Images drawn using a software version of the algorithm are presented and discussed.