Showing papers in "IEEE Computer Graphics and Applications in 1990"
TL;DR: The discussion covers NetCDF data abstraction and interface; dimensions, variables, and attributes; direct access and hyperslab access, the netCDF library; the data format; ncdump and ncgen utilities; experience, usability, and performance; limitations of NetC DF; and future plans.
Abstract: The network common data form (NetCDF), a data abstraction for storing and retrieving multidimensional data, is described. NetCDF is distributed as a software library that provides a concrete implementation of that abstraction. The implementation provides a machine-independent format for representing scientific data. Together, the abstraction, library, and data format support the creation, access, and sharing of scientific information. NetCDF is useful for supporting objects that contain dissimilar kinds of data in a heterogeneous network environment and for writing application software that does not depend on application-specific formats. Independence from particular machine representations is achieved by using a nonproprietary standard for external data representation. The discussion covers NetCDF data abstraction and interface; dimensions, variables, and attributes; direct access and hyperslab access, the NetCDF library; the data format; ncdump and ncgen utilities; experience, usability, and performance; limitations of NetCDF; and future plans. >
684 citations
TL;DR: The aim is to provide readers with enough background and insight on the various methods to allow them to choose the algorithm best suited to their needs and to help identify the areas that need more research and point to possible solutions.
Abstract: The various types of shadows are characterized. Most existing shadow algorithms are described, and their complexities, advantages, and shortcomings are discussed. Hard shadows, soft shadows, shadows of transparent objects, and shadows for complex modeling primitives are considered. For each type, shadow algorithms within various rendering techniques are examined. The aim is to provide readers with enough background and insight on the various methods to allow them to choose the algorithm best suited to their needs and to help identify the areas that need more research and point to possible solutions. >
319 citations
TL;DR: An investigation of the quality of surface-shading algorithms using computer-simulated test objects is reported, and it was found that gray-level gradient shading and marching cubes did not differ greatly, except for thin objects, where adaptive gray- level gradient shading was better.
Abstract: An investigation of the quality of surface-shading algorithms using computer-simulated test objects is reported. Test results are presented for four algorithms: z-buffer gradient, gray-level gradient, adaptive gray-level gradient, and marching cubes with two extensions. It was found that gray-level gradient shading and marching cubes did not differ greatly, except for thin objects, where adaptive gray-level gradient shading was better. Transparent visualization using transparent gray-level gradient shading is examined. It is shown that although there is no way to assure the fidelity of transparent shading, it is useful when no other surface at all can be determined. Use of a combination of shading methods appears to yield the best visualization of the respective objects. >
272 citations
TL;DR: Volume rendering, a technique for visualizing sampled functions of three spatial dimensions by computing 2-D projections of a colored semitransparent volume, is extended to handle polygonally defined objects using a hybrid ray-tracing algorithm.
Abstract: Volume rendering, a technique for visualizing sampled functions of three spatial dimensions by computing 2-D projections of a colored semitransparent volume, is extended to handle polygonally defined objects. A hybrid ray-tracing algorithm, whereby rays are simultaneously cast through a set of polygons and a volume data array, is used. Samples of each are drawn at equally spaced intervals along the rays, and the resulting colors and opacities are composited together in depth-sorted order. To avoid aliasing of polygonal edges at modest computational expense, a form of selective supersampling is used. To avoid errors in visibility at polygon-volume intersections, special treatment is given to volume samples lying immediately in front of and behind polygons. The cost, image quality, and versatility of the algorithm are evaluated using data from 3-D medical imaging applications. >
257 citations
TL;DR: Computer-assisted surgery (CAS), a new navigation aid for skull-base surgery, is discussed, which combines 3-D coordinate measurement techniques, voxel processing methods, and pseudo-3-D image presentations to support preoperative planning of therapy, path-finding during the operation itself, and postoperative therapy control.
Abstract: Computer-assisted surgery (CAS), a new navigation aid for skull-base surgery, is discussed. The system described combines 3-D coordinate measurement techniques, voxel processing methods, and pseudo-3-D image presentations to support preoperative planning of therapy, path-finding during the operation itself, and postoperative therapy control. The surgeon employs a hand-guided electromechanical 3-D-coordinate digitizer to locate points of interest within the operative field. The coordinates measured this way are correlated with a voxel model of the object gained by a preceding computed-tomography examination. With a prototype system the accuracy of this method has proven to be better than +or-1 mm. The system has been successfully applied in more than 60 ear-nose-throat operations and four neurosurgical procedures. The computer hardware and integration of the system into an experimental picture archiving and communication system are discussed. >
242 citations
TL;DR: The methods and algorithms used for volumetric rendering of medical computed tomography data are described in detail and a step-by-step description of the process used to generate two types of images is included.
Abstract: The methods and algorithms used for volumetric rendering of medical computed tomography data are described in detail. Volumetric rendering allows for the use of a mixture paradigm for representation of the volume to be rendered and uses mathematical techniques to reduce or eliminate aliasing. A step-by-step description of the process used to generate two types of images (unshaded and shaded surfaces) is included. The technique generates three-dimensional images of computed tomography data with unprecedented image quality. Images generated with this technique are in routine clinical use. >
213 citations
TL;DR: An interactive method of behavioral animation in which the user controls motion by designing a network mapping sensor information to effectors is described, called Notion.
Abstract: Behavioral animation is a means for automatic motion control in which animated objects are capable of sensing their environment and determining their motion within it according to certain rules. An interactive method of behavioral animation in which the user controls motion by designing a network mapping sensor information to effectors is described. The system is called Notion. The network consists of sensors (such as distance to other objects and recognition of their qualities) and effectors (here, jet motors propel objects) connected by nodes and connections. Nodes, which embody such responses as attraction, avoidance, arbitration, and their outputs, map sensory stimuli to effector responses. Sensors, nodes, and effectors are given set limits. Such limits, together with an interactive window environment for altering the network, make it possible to explore a variety of motions quickly. >
180 citations
TL;DR: An algorithm that can produce planes or contours through the volume without any loss of the volume resolution of the original data set is presented and is particularly well suited for three-dimensional magnetic resonance images.
Abstract: It is shown how to generate oblique slices from a set of parallel slices. An algorithm that can produce planes or contours through the volume without any loss of the volume resolution of the original data set is presented. The algorithm uses the Fourier-shift theorem and is efficient for calculating large numbers of slices. Although the algorithm is general, it is particularly well suited for three-dimensional magnetic resonance images, as demonstrated with examples. >
161 citations
TL;DR: A toolkit known as apE, which was an acronym for animation production environment, is presented and common elements in building any graphics system as well as elements particular to building a large system are examined.
Abstract: A toolkit known as apE is presented. Originally, this was an acronym for animation production environment, but apE has become known as a software designed for more than just animation. Previous work is briefly reviewed, and the processing of designing the system is discussed. Common elements in building any graphics system as well as elements particular to building a large system are examined. The design and construction of apE 1.1 and apE 2.0 are described. The policy governing the distribution of apE and the advantages of academic software development are discussed. >
160 citations
TL;DR: A procedure for defining and recognizing shape features 3-D solid models is presented in which a shape feature is defined as a single face or a set of continuous faces possessing certain characteristic facts in topology and geometry.
Abstract: A procedure for defining and recognizing shape features 3-D solid models is presented in which a shape feature is defined as a single face or a set of continuous faces possessing certain characteristic facts in topology and geometry. The system automatically extracts these facts from an example shape feature interactively indicated by the user. The resulting representation of the shape feature can be interactively edited and parameterized. Graph matching accomplishes feature recognition. The system searches the solid model for B-rep subgraphs with the same characteristic facts as the shape feature to be recognized. When the system recognizes a shape feature, it removes the geometry associated with the feature from the original solid model to produce a simpler solid model. It then examines the simpler solid model to determine whether additional features have been revealed. The process repeats until no additional features are found. >
146 citations
TL;DR: The surface-removal method creates a set of surfaces internal to a given object, so that, given a specified distance, every point on the created surfaces is equidistant from the surface of the enclosing object.
Abstract: A flexible graphics system for displaying functional and anatomic data on arbitrary collections of surfaces on or within the brain is presented. The system makes it possible to show complex, convoluted surfaces with the shading cues necessary to understand their shapes; to vary viewpoint, object position, illumination, and perspective easily; to show multiple-objects in one view, with or without transparency, in order to examine internal surfaces and intersecting objects in relation to each other; and to superimpose quantitative information on biological or otherwise defined surfaces anywhere within the volume, thus furthering understanding of both quantitative and positional information in its global context. These display techniques are applied to a new form of biological surface model, the removed surface. The surface-removal method creates a set of surfaces internal to a given object, so that, given a specified distance, every point on the created surfaces is equidistant from the surface of the enclosing object. The method is based on thresholding a derived scalar field, the minimum distance field. Models made by this method have applications in 3-D neurobiology and provide an alternative to cutaways for viewing patterns of internal functional activity. >
TL;DR: It is shown how to determine the severity of ill conditioning and how to obtain physically meaningful solutions without excessive computations, even when dealing with extremely ill-conditioned configurations.
Abstract: Realistic motion simulation for articulated figures has relied on the solution of linear systems of equations. Sometimes the solution of these equations presents a great deal of numerical difficulty, resulting in unrealistic or spurious motion for the figure or in excessive computation because of small integration intervals. The cause of the difficulty is shown to be related to the physical structure of the figure, not the mathematical formulation. It is shown how to determine the severity of ill conditioning and how to obtain physically meaningful solutions without excessive computations, even when dealing with extremely ill-conditioned configurations. >
TL;DR: A method for finding an adaptive polygonal approximation of an implicitly defined surface that yields an approximation guaranteed accurate to within some user-specified tolerance of the actual surface.
Abstract: A method for finding an adaptive polygonal approximation of an implicitly defined surface is presented. For algebraic surfaces, the method yields an approximation guaranteed accurate to within some user-specified tolerance of the actual surface. This polygonalization can then be rendered using standard shaded polygon drawing techniques. A method for eliminating or improving the aspect ratios of the 'skinny' polygons that often arise in traditional polygonalization methods is also presented. This method has proved particularly useful in the creation of polygonalization for finite-element analysis. >
TL;DR: Techniques for the visualization of a scalar-valued function defined over a spherical domain are discussed, and the projected graph technique can be considered as a method for modeling closed surfaces.
Abstract: Techniques for the visualization of a scalar-valued function defined over a spherical domain are discussed. Functions of this type arise, for example, in the fitting of measured data on the surface of the earth. Methods for contouring and for displaying the graph of a function are presented, along with several examples. The projected graph technique can also be considered as a method for modeling closed surfaces. >
TL;DR: The radiosity algorithm is extended to dynamic environments, providing global-illumination simulations to scenes that are modified interactively, and yields excellent approximations to the exact solutions at interactive speeds.
Abstract: The radiosity algorithm is extended to dynamic environments, providing global-illumination simulations to scenes that are modified interactively. The illumination effects introduced by a change in position, shape, or attributes of any object in the scene are computed very rapidly by redistributing the energy already exchanged between objects. Corrections are made by shooting positive and negative energy, accounting for increased illumination and the creation of shadows. Object coherence is used to minimize computation, and progressive-refinement techniques are used to accelerate convergence. The extended algorithm yields excellent approximations to the exact solutions at interactive speeds. >
TL;DR: An approximate numerical reparameterization technique that improves on a previous algorithm by using a different numerical integration procedure that recursively subdivides the curve and creates a table of the subdivision points is presented.
Abstract: Specifying constraints on motion is simpler if the curve is parameterized by arc length, but many parametric curves of practical interest cannot be parameterized by arc length. An approximate numerical reparameterization technique that improves on a previous algorithm by using a different numerical integration procedure that recursively subdivides the curve and creates a table of the subdivision points is presented. The use of the table greatly reduces the computation required for subsequent arc length calculations. After table construction, the algorithm takes nearly constant time for each arc length calculation. A linear increase in the number of control points can result in a more than linear increase in computation. Examples of this type of behavior are shown. >
TL;DR: Comparisons of identical scenes rendered with a conventional ray tracer and the Ray tracer presented incorporating a polarization model show that the present method renders specular interobject reflections more accurately with respect to reflected radiance and color.
Abstract: Incorporating polarization parameters into the lighting model can enhance the physical realism of images rendered with a ray tracer. Polarization effects can be important in certain scenes, and the difference in rendering even simple scenes with and without proper treatment of polarization can be striking. All light waves possess a state of polarization, which changes almost every time light reflects off a material surface. A single reflection partially polarizes and may even completely polarize previously unpolarized light. Polarization influences the rendering of a scene because the reflected radiant intensity depends largely on the incident light waves's polarization state. E. Wolf's (1959) coherence matrix formalism of polarization has been incorporated into the Torrance-Sparrow reflectance model. This combination allows elegant quantitative derivations of the altered polarization state of light upon reflection in a ray tracer. Comparisons of identical scenes rendered with a conventional ray tracer and the ray tracer presented incorporating a polarization model show that the present method renders specular interobject reflections more accurately with respect to reflected radiance and color. >
TL;DR: An approach to the problem of comparative analysis of objects and their surfaces that arises in medical imaging is presented and illustrated with an application to postsurgical bone-graft separation.
Abstract: An approach to the problem of comparative analysis of objects and their surfaces that arises in medical imaging is presented and illustrated with an application to postsurgical bone-graft separation. A common requirement in medical imaging applications is the registration of multiple representations of the object prior to mensuration. The modeling of the registration process and the registration system are described. The measurement of change in volume of bone grafts implanted inside the human body in a corrective surgical procedure is discussed, and the results are evaluated. >
TL;DR: A survey of some techniques that may have potential for free-form modeling with algebraic surfaces is continued, although many of the ideas presented have application togebraic surfaces of any degree.
Abstract: A survey of some techniques that may have potential for free-form modeling with algebraic surfaces is continued. Classical results as well as several recent innovations are included. Specific attention is paid to cubic algebraic surfaces, although many of the ideas presented have application to algebraic surfaces of any degree. Topics addressed include piecewise constructions, interpolation to points and space curves, and parameterization. >
TL;DR: A geometrically continuous subclass of Catmull-Rom splines based on geometric continuity and possessing shape parameters is discussed, which leads to the development of geometric constructions for quadratic G/sup 1/ and cubic G/Sup 2/ Beta-splines.
Abstract: Some observations are made concerning the source and nature of shape parameters. It is then described how Bezier curve segments can be stitched together with G/sup 1/ or G/sup 2/ continuity, using geometric constructions. These constructions lead to the development of geometric constructions for quadratic G/sup 1/ and cubic G/sup 2/ Beta-splines. A geometrically continuous subclass of Catmull-Rom splines based on geometric continuity and possessing shape parameters is discussed. >
TL;DR: In this article, a parallel line and circle drawing algorithm based on J.E.Bresenham's algorithm is presented. But it is assumed that the algorithm are run in a multiple-instruction-multiple-data (MIMD) environment, that the raster memory is shared, and that the processors are dedicated and assigned to the task (of line or circle drawing).
Abstract: Parallel algorithm for line and circle drawing that are based on J.E. Bresenham's line and circle algorithms (see Commun. ACM, vol.20, no.2, p.100-6 (1977)) are presented. The new algorithms are applicable on raster scan CRTs, incremental pen plotters, and certain types of printers. The line algorithm approaches a perfect speedup of P as the line length approaches infinity, and the circle algorithm approaches a speedup greater than 0.9P as the circle radius approaches infinity. It is assumed that the algorithm are run in a multiple-instruction-multiple-data (MIMD) environment, that the raster memory is shared, and that the processors are dedicated and assigned to the task (of line or circle drawing). >
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TL;DR: Ray-tracing methods are extended to include the mirage effect by simulating atmospheric variations by distinguished air layers, each layer being assigned a refractive index which causes a penetrating light ray to bend in accordance with Snell's law of refraction.
Abstract: Ray-tracing methods are extended to include the mirage effect. This is accomplished by simulating atmospheric variations. Different air layers are distinguished in modeling the continuous spectrum of temperature change, each layer being assigned a refractive index, which causes a penetrating light ray to bend in accordance with Snell's law of refraction. A classification of mirage images is included. >
TL;DR: A model that balances image realism, model complexity, and runtime efficiency and is easier than its predecessors for inexperienced animators to use is presented.
Abstract: Because of the problems inherent in modeling the physics of light transmission, all lighting models used in computer graphics are approximations. Each model provides a different balance between image realism, model complexity, and runtime efficiency. A model that balances these factors and is easier than its predecessors for inexperienced animators to use is presented. >
TL;DR: Applications of solid modeling in computer-aided design, computer- aided manufacturing, and robotics, which often involve aggregates or assemblies of disconnected pieces, are addressed and an alternative CSG-like formalism based on open sets is presented.
Abstract: Applications of solid modeling in computer-aided design, computer-aided manufacturing, and robotics, which often involve aggregates or assemblies of disconnected pieces, are addressed. Models for such assemblies must be subjected to some of the same operations as models for single parts. The mathematical basis of constructive solid geometry (CSG), the usual formalism in solid modelers, leads to difficulties in dealing with assemblies. An alternative CSG-like formalism based on open sets, in which both assemblies and connected pieces are modeled as point sets is presented. Consequently the same Boolean operations apply uniformly to connected pieces and assemblies. >
TL;DR: The author comments on an article by M. Berger et al. which describes a model for forming a mirage, and points out that the primary bending agent in mirage formation is total reflection, not refraction, which indicates that a purely reflective model, without refraction might well be sufficient.
Abstract: The author comments on an article by M. Berger et al. (ibid., vol.10, no.3, p.36-41, 1990), which describes a model for forming a mirage. In particular, he makes some points regarding their interpretation of the model and their description of their implementation of a version of it. He points out that the primary bending agent in mirage formation is total reflection, not refraction, as Berger et al. suggest. This in turn indicates that a purely reflective model, without refraction might well be sufficient. The author asserts that this would be beneficial, as dispersive ray tracing is not particularly easy or inexpensive to implement, and it would obviate the statement by Berger et al. that the use of layers allows a digitized approach to the continuous spectrum. A response by M. Berger, essentially agreeing with the author, is included. >
TL;DR: The application of nonlinear median and alpha-trimmed mean filters to computer graphics is discussed and a series of examples shows that the filters eliminate spike noise in a stochastic sampling application without smearing the final image.
Abstract: The application of nonlinear median and alpha-trimmed mean filters to computer graphics is discussed. The filters are simple to implement, do not require large amounts of CPU time to execute, and can be applied iteratively for better control over the filtering effects. A series of examples shows that the filters eliminate spike noise in a stochastic sampling application without smearing the final image. >
TL;DR: The tutorial presents some tools for free-form modeling with algebraic surfaces, that is, surfaces that can be defined using an implicit polynomial equation f(x, y, z)=0.
Abstract: The tutorial presents some tools for free-form modeling with algebraic surfaces, that is, surfaces that can be defined using an implicit polynomial equation f(x, y, z)=0. Cubic algebraic surfaces (defined by an implicit equation of degree 3) are emphasized. While much of this material applies only to cubic surfaces, some applies to algebraic surfaces of any degree. This area of the tutorial introduces terminology, presents different methods for defining and modeling with cubic surfaces, and examines the power basis representation of algebraic surfaces. Methods of forcing an algebraic surface to interpolate a set of points or a space curve are also discussed. The parametric definition of cubic surfaces by imposing base points is treated, along with the classical result that a cubic surface can be defined as the intersection locus of three two-parameter families of planes. Computer-generated images of algebraic surfaces created using a polygonization algorithm and Movie. BYU software illustrate the concepts presented. >
TL;DR: The particle-system technique is used to model 'fuzzy objects', i.e. objects not bounded by well-defined, easily visible surfaces, to depict, in real time, ship wakes in an air/sea simulation using a high-speed workstation for graphics calculation and display.
Abstract: The particle-system technique is used to model 'fuzzy objects', i.e. objects not bounded by well-defined, easily visible surfaces. the technique is used to depict, in real time, ship wakes in an air/sea simulation using a high-speed workstation for graphics calculation and display. The system consists of a graphics workstation tied to a compute server (typically a minicomputer, mainframe, or parallel processor, depending on the simulation complexity). The compute server executes the dynamic models associated with the vehicles in the simulation. The position and attitude of each vehicle are periodically transmitted to the graphics workstation, where a rendering of the situation is produced and displayed. Such a system normally runs at a frame redraw rate of 10 frames per second or greater to sustain an illusion of smooth movement. The ship wake phenomenon and its modeling, including some simplifications, are described. >
TL;DR: A simple method is presented for eliminating most pixel-positioning errors when rendering lines and polygons with J.E. Bresenham's algorithm, which eliminates all dropouts and virtually all overlaps between adjacent polygons whose edges lie on the same line.
Abstract: A simple method is presented for eliminating most pixel-positioning errors when rendering lines and polygons with J.E. Bresenham's algorithm (see IBM Syst. J., vol.4, no.1, p.25-30 (1965)). The method affects only the calculation of the initial values for Bresenham's vector-generating algorithm. It does not alter the actual vector-generating algorithm, requiring only inter arithmetic to find the next pixel in a vector. The method eliminates all dropouts and virtually all overlaps between adjacent polygons whose edges lie on the same line. This eliminates the need to grow polygons to avoid dropout and opens the possibility of drawing surfaces composed of adjacent polygons with read modify/write pixel operations such as add or alpha buffering. It is shown that most rendering artifacts of today's display controllers ultimately result from pixel-positioning errors, not insufficient z-buffer resolution. >
TL;DR: The author describes how the unique configuration of the planet Uranus influenced him to take a close look at how the layout of a texture map in memory affects the performance of the rendering algorithm.
Abstract: The author describes how the unique configuration of the planet Uranus influenced him to take a close look at how the layout of a texture map in memory affects the performance of the rendering algorithm. A planet rendering program that calculates, for each occupied pixel on the screen, the latitude and longitude visible at that pixel, is described. It uses this latitude and longitude to index into a texture map to get a surface color. The actual texture color comes from bilinearly interpolating the texture colors at the four texture map pixels that surround that latitude and longitude. This, along with the shading calculations, gives the net color of the pixel. The use of virtual memory, handling page faults, tiling, and address generation are considered. >