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From Perspectives to Holography

Published onApr 23, 2021
From Perspectives to Holography

Drawing a perspective is a procedure for visualization, a procedure that has suffered from faddism in computer graphics, a procedure that can unfairly influence the process of creating physical form. Alberti’s formalization of perspective in 1432 helped foster the Renaissance preoccupation for the observer and the viewing position (and possibly symmetry). Later, when man regularly built above six stories, the “bird’s eye” and the “worm’s eye” view made the stationary viewer even more manifest. Photography even further reinforced this syndrome.

Finally, the movie camera relieved the stationary-observer obsession by allowing the consideration of a path of movement and rotations of a field of vision. Cinematographic methods, however, were cumbersome, and the film processing time made movie-making a presentation procedure (off-line) rather than a study medium (on-line). Then came the instantaneous images of closed-circuit television. Coupled with a model scope or fiber-optics cord (optical devices for visually placing oneself within scale models), a designer could push his way through a model to simulate roughly the visual experience. Unhappily, television techniques are unwieldy.

The computer is a natural medium for the mass production of perspective images. At first, numerically controlled plotters were employed to draw perspectives at hundreds of small increments along a path. These drawings were then filmed with animation procedures to produce a cartoon of moving figures (Fetter, 1964), a general procedure more cumbersome than any previous method. Then the plotter was replaced with the cathode-ray tube in anticipation of creating perspective drawings (in their appropriate transformations) at a rate of sixteen to twenty frames per second, for providing the illusion of traveling through an environment at any speed and in a flicker-free manner (Negroponte, 1966). Assume that on the screen of a cathode-ray tube we have a perspective drawing, derived from the machine’s model of some project. The rendered perspective is a crude jungle of lines describing a wire frame structure. Larry Roberts (1963) has taken out the hidden lines, David Evans et al. (1967) have put in halftones, and everybody is trying to perform the perspective transformations in real time.

Meanwhile, General Electric’s Electronics Laboratory, Syracuse, New York, under NASA contract, has developed a special-purpose computer that permits a viewer to voyage through an environment with hidden lines removed, with halftones, in real time, and in color. Furthermore, the user of this system commands the movement with an aircraft-type control stick that delivers him a motor involvement with the visual simulation. P. Kamnitzer of U.C.L.A. is presently applying the NASA-General Electric system to urban visual simulation problems (Kamnitzer, 1969).

The history is long; the list of participants is long (M. Milne, 1969). Why the great concern with perspectives? First, the problem is intrinsically natural for computer graphics studies, its formulation is technically difficult (thus stimulating), and it requires no examination of design philosophy.

da Vinci: “Le Prospectographe,” drawing circa 1488. (Courtesy of Biblioteca Ambrosiana, Milan)

Durer: “Le Dessinateur de la femme couchée,” engraving, 1525.

Six frames of a computer graphics film on visibility studies of an aircraft carrier landing. The film was made by William Fetter for the Boeing Company. The last ten seconds of the carrier landing required two hundred and forty computer-drawn perspectives to be plotted, touched up by an artist, and then filmed. (Illustrations courtesy of the Boeing Company)

Three black and white photographs of Peter Kamnitzer’s color display at the Visual Simulations Laboratory of General Electric. The images are from the CITY-SCAPE program, and they are presently restricted to 240 edges per frame. (Photographs courtesy of Peter Kamnitzer)

Durer: “Le Portraitiste,” engraving circa 1525. (Courtesy of the Bibliothèque nationale, Paris)

A rendering made to study the effects of increasing to 1,500 edges in the above system. (Courtesy of Peter Kamnitzer)

Larry Roberts’ Wand. (Courtesy of Lincoln Laboratories)

A stereoscopic viewing attachment on a large cathode-ray tube. This attachment was designed by C. F. Mattke for use by Michael Noll in his investigation of three-dimensional man-machine communication, performed at the Bell Telephone Laboratories. (Photograph courtesy of Michael Noll)

An electromechanical device used for input of threedimensional data. The device is much like an aircraft joy stick and is coupled with the adjacent stereoscope. (Photograph courtesy of Michael Noll)

Perspective is a natural procedure for representing in two dimensions the illustration of a three-dimensional event. On a picture plane a trace of points defines the intersection of imaginary lines between a monocular observer and the real or unreal world. When the picture plane is removed from this world and viewed from the same vantage point, the image is an accurate representation with no distortion. The mode thus affords an appropriate visual representation of the visual aspects of an architectural real world. But, with future threedimensional displays and input mechanisms, the virtuous role of the perspective drawing surely will be diluted. As Coons states, “In a few years from now (April 1968) you (a group of architects) will be able to walk into a room and move your hand and have a plane or surface appear before you in light. You will be able to build a building in light so that you can walk around it and change it” (Herzberg, 1968).

The dramatics of such dazzling statements stem from the age-old desire of the architect to be able to lift his pencil, gesticulate in midair, and have the stylus ooze out lines that float in space. Part of this desire has already been fulfilled by an ultrasonic position-sensing device. Larry Roberts’ Lincoln Wand allows the computer (within a work space of ninety-six cubic feet) to track the x-y-z position (to the nearest one-fifth of an inch) of a hand-held, pen-size device (Roberts, 1966). Four ultrasonic transmitters recurrently pulse bursts of energy, and the Wand reports to the computer the time at which it heard each signal. The computer uses three time lengths to determine trigonometrically the pen’s position; the fourth transmitter provides a geometric check on the measurements. Unfortunately, the Wand does not leave traces in midair upon which to build consecutive lines (which aggravates the problem of hand trembling). Though a three-dimensional model is being constructed within the machine, the output associated with the Wand is at present a perspective or axonometric display.

Ivan Sutherland’s helmet. (Courtesy of Ivan Sutherland)

The Direct-View Three-Dimensional Display Tube developed at Hughes Research Laboratories by R. D. Ketchpel (1963). In contrast to other presentations in which the third dimension is simulated stereoscopically, this device displays the information in actual space. The three-dimensional display tube utilizes a phosphor-coated disc spinning at 900 rpm. Upon excitation by a cathode-ray beam at selected times, any point in the volume “swept out” may be illuminated thirty times a second. (Photograph courtesy of R. D. Ketchpel)

This illustration is a direct positive print of a hologram of the model to the left. If viewed as a transparency with a coherent light source behind, this hologram would display the model in three dimensions.

Further efforts will eventually allow threedimensional displays to be joined with wandlike devices. Ivan Sutherland is creating a machine that gives the illusion of actually walking around and within visual models (I. Sutherland, 1968). The device is a helmet mounted with two eyeglass-size cathode-ray tubes (with prisms) that permit stereoscopic images to be transformed in accordance with the head position of the wearer. In this case three antennas report the user’s position, but the movement could also be monitored with the user driving a simulated car and actually driving through a city that does not exist in the real world. With halftones, color, and real time, this technique would afford an excellent simulation of the visual world. Sutherland’s device even allows for a split image, through the prisms, that permits the designer to view his project overlaid upon the visual real world.

Another three-dimensional display technique is holography (Gabor, 1948). TV Guide periodically tempts its readers with threedimensional television: ballet dancers in your living room and the Tonight Show in your bed. In hologram television, “the pictures have a realism unattainable by any other means. The three-dimensional effect is obtained without the need for a stereo pair of pictures, and without the need for any devices such as Polaroid glasses. In addition, all the visual properties of the original scene, such as parallax between near and far objects in the scene, and a change in perspective as a function of the observer’s viewing position, are present” (Leith and Upatnieks, 1965). This apparition is achieved by recording the interference patterns of two sources of coherent light (usually lasers), one reflected directly from the object and the other by a mirror.

At present, efforts are being conducted to construct through computation synthetic holograms for simple geometric configurations (Lesem et al., 1968). One method calculates the interference patterns and plots the result on a transparency. Another method positions a small mirror in three-dimensional space and traces the configuration in the presence of the necessary light sources, in effect, taking a time-lapse hologram (Stroke and Zech, 1966). So far, neither method is in real time.

When computers can simulate holograms in real time (using some flat-screen television technique), views of the machine’s mathematical model could be selected in a general manner, and the designer’s head movements could supply specific vantage points. Soon, on a display device, architects will have glimpses of physical environments that do not exist. These witnessings will be in full color, with halftones, and in three dimensions.

The reader must remember that these apparently ghostlike images are only visual simulations. Though the better ones will furnish a motor involvement with the designer, the devices that have been discussed do not delve into the crucial problem of machine response to nonvisual involvement with the environment: auditory simulation, tactile presence, feeling of a breeze in a lonely space.

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