Browse Prior Art Database

Techniques for Displaying Solid Objects on a Varifocal Mirror

IP.com Disclosure Number: IPCOM000077521D
Original Publication Date: 1972-Aug-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 5 page(s) / 107K

Publishing Venue

IBM

Related People

Appel, A: AUTHOR [+3]

Abstract

The technique described herein enables the displaying of solid objects on a varifocal mirror volumetric display. Heretofore, it has been possible to display only discrete points or simple entities on such device.

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Techniques for Displaying Solid Objects on a Varifocal Mirror

The technique described herein enables the displaying of solid objects on a varifocal mirror volumetric display. Heretofore, it has been possible to display only discrete points or simple entities on such device.

The technique consists of three programs which are used to control an interactive graphics display device which, when used with a varifocal mirror, can produce a volumetric display of solid objects. The examples of the solids presented herein are imaginary and are suitably polyhedra, but the technique can be readily applied to depict higher order curves and surfaces.

A suitable experimental apparatus for testing the programs to be described may be an interactive graphics display device, which is employed to display the graphic orders that are viewed as they are reflected by a varifocal mirror. The varifocal mirror is suitably a sheet of aluminized MYLAR* clamped between steel flanges and mounted in front of a loud speaker. As the loud speaker is energized, the sheet of aluminized MYLAR vibrates and forms a curved mirror with a constantly changing radius. There is illustrated the physics of the varifocal mirror in Fig. 1. As seen in this figure, the position of the virtual image of such a mirror is determined by its radius. F is the focal point, C is the center of curvature, f is the focal distance, S is object distance and S' is the image distance. From the arrangement shown f = -R/2 1/S + 1/S, = -2/R = 1/f.

The variation in radius and the illusionary change in virtual image location can be used to produce a volumetric display.

The signal activating the loud speaker is generally a continuous sine wave. The variation of depth in time, is as shown in the curve of Fig. 2A. In this curve, the abscissa is time and the ordinates are R i.e., radius of the mirror and D i.e., depth of a virtual image. As seen in Fig. 2B, a portion of the display depth is substantially linear. Thus, if the processing of the display list of an interactive graphics device is synchronized with the vibrations of a mirror, such that the display elements are displayed at the instant that the virtual image depth has the depth that is desired for each display element, then a volumetric effect will be produced in the mirror. In the following table, there is shown the relationship of the display list and the instant at which the elements of the display list are to be respectively displayed. Display Instant To Be

List Displayed

P(1) T(1)

L(1) T(2)

P(2) T(3)

P(3) T(4)

. .

. .

. .

. .

. .

1

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. .

P(M) T(N).

In accordance with the method disclosed herein, there are provided the following:

1) A volumetric display program which reads in the scene to be displayed in three dimensions.

2) A program which calculates the intersection of a polyhedron with a series of parallel planes.

3) A program which calculates a series of points in space which approximate the lines of a polyhedron.

By the use of...