Representation Of Three-dimensional Objects Research Articles

Computers: The computer graphics revolution: Slowly but surely, new software and hardware are making a reality of graphics specialists' dreams

Computer graphics is beginning to transform the way a large part of the data-processing industry operates. New software and hardware developed over the past several years have made practicable the accurate representation of three-dimensional objects of great complexity. This new capability, using computers of reasonable size and cost, has opened a widening field of applications.

A flexible computer-controlled perception laboratory

Research in perception is often guided or limited by the capabilities of the laboratory. A computer-controlled perception laboratory is described that was designed to be extremely flexible at a modest cost. The laboratory permits control of onset time, offset time, and intensity of visual, auditory, and tactile stimuli. The visual stimuli include single points, text, stereoscopic displays, and two-dimensional representations of three-dimensional objects moving in space. The design of the hardware and software and the criteria that guided our choice of this design are discussed. Finally, potential applications of this laboratory are considered.

Decomposition of Three-Dimensional Objects into Spheres

Algorithms are presented for converting between different three-dimensional object representations: from a collection of cross section outlines to surface points, and from surface points to a collection of overlapping spheres. The algorithms effect a conversion from surface representations (outlines or surface points) to a volume representation (spheres). The spherical representation can be useful for graphical display, and perhaps as an intermediate representation for conversions to representations with other primitives. The spherical decomposition also permits the computation of points on the symmetric surface of an object, the three-dimensional analog of Blum's symmetric axis. The algorithms work in real coordinates rather than in a discrete space, and so avoid error introduced by the quantization of the space.

The representation of three-dimensional objects

The representation of three-dimensional objects

New Concepts for Three-Dimensional Shape Analysis

A new approach to machine representation and analysis of three-dimensional objects is presented. The representation, based on the notion of "skeleton" of an object leads to a scheme for comparing two given object views for shape relations. The objects are composed of long, thin, rectangular prisms joined at their ends. The input picture to the program is the digitized line drawing portraying the three-dimensional object. To compare two object views, two characteristic vertices called "cardinal point" and "end-cardinal point," occurring consistently at the bends and open ends of the object are detected. The skeletons are then obtained as a connected path passing through these points. The shape relationships between the objects are then obtained from the matching characteristics of their skeletons. The method explores the possibility of a more detailed and finer analysis leading to detection of features like symmetry, asymmetry and other shape properties of an object.

Procedural Representation of Three-dimensional Objects

A system of PL/I procedures has been written that permits geometric objects to be described hierarchically. The objects are themselves represented as PL/I procedures, allowing very general use of variables. By effectively intercepting subprogram calls, the system provides a means of modifying the semantics associated with any object without modifying the object's procedural description.