A 3D Volumetric Display Using A Rotating Helix

These are animated views of my opaque helix...

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Intro Apps Scene Production Why a Triple Helix? Construction Materials Resources Latest Info Links

Introduction

Conventional televisions and monitors are fine for pictures; however, they only provide a two-dimensional viewing area. This poses a problem for the growing field of graphic arts design. Designers have tried to create more realistic scenes through shading. This produces a dramatic feeling of depth, but one can't truly see the entire scene. It's like looking through a window. There is only one point of view. (See references 5 and 6)

Scientists have tried long and hard to overcome this difficulty. Some innovations used holography techniques, lasers aimed at a florescent floride glass cube, cathode-ray sphere (a round picture tube), a spinning helical screen, illusions like the magic eye, and many others. (See References 1,2,3,4,6, and 7)

The rotating helix is a promising approach. As it spins, a continuous point of light projected onto it is extruded, or stretched into a vertical line. A circle will become a cylinder, a square will become a rectangular prism, and so on. More complex objects may be created by sequencing intermittent points with a computer animation. Such shapes can be seen from any angle by simply walking around the helix. There's no awkward glasses or special equipment required to see the designs, just your eyes. This method of using a moving screen is called a swept-display because the screen sweeps out an image layer by layer. It would be cheap as well. The only materials needed to build it are paper or fine cloth and a wooden or plastic helix-shaped support frame.

Of course, someone had already thought of this method of displaying 3-d. However, the original used a high-speed scanning laser to do the projecting on a double helix while I am using either a high-speed LCD on an overhead or a projection TV tube to show a computer generated animation on a triple helix to increase the clarity of the picture. (See references 3, 5, and 2) The triple helix is necessary for the projector to keep up with the animation. Most can only flash 60 frames a second. More on that later.

Applications

Uses for this technology are staggering. This type of display can be easily operated by the medical, drafting, contracting, air-traffic control, and recreational industries. Doctors could quickly and effectively reconstruct a three-dimensional image from the jumbled mess of C.A.T. scanned slices taken from a patient. Drafters and contractors would be able to correctly visualize their creations thereby minimizing errors. Air-traffic will no longer need to rely on those flat radar screens, giving no depth and endangering pilots. Recreation would be greatly affected. Giant helixes could be built with a clear room in the center to make a player completely immersed in a 3-d game. Panoramic televisions could be constructed giving every viewer their own perspective. (See references 3,4,5, and 6)

Of course, the idea of panoramic TV's isn't going to take shape until well into the future when it is more fully supported. At the moment, only two dimensions are recorded by cameras. The third's information, which is necessary for 3-d television, is lost. At best, the converted television signal would end up as merely a flat image. One could tile different channels around the helix though, resulting in the end of children's' arguments concerning what channel to watch.

Scene Production

Before I get into the making of 3-d scenes, the basics must be covered. Pixel really isn't a correct term for 3-d purposes. Pixels are two-dimensional, having only height and width. Three-dimensional pixels are called voxels. An animation is made up of a series of individual pictures called frames, which are played back in order faster than the human eye can detect creating the illusion of motion.

Making an animation from scratch suitable for playback on the helix is a little time consuming. Each voxel that is meant to be on the same slice of the scene is to be put on a separate frame. This is because if the helix were stopped for an instant and the entire top row of the image were projected onto the helix, it would become a diagonal line. Only three radii of voxels can be in a single vertical position at any moment, one for every helix. Each frame looks like a blinking star. The helix must be allowed to catch up with the other voxels. This must be done at least 16 times the rate of rotation. This is found by subdividing the number of helii. Thereafter, the next slice is done, again, one line of voxels at a time, but instead of making another 56 frames, the second slice's voxels are placed next to the first's. The resulting animation would obviously be gibberish on a conventional television, but it would be crystal clear on the helix.

Why a Triple Helix?

If I had a Single helix, I would need many more frames in the animation; the helix would need to rotate three times faster, and the projection method would need to be able to flash three times faster. A triple helix decreases all of these numbers by one third, bringing the flash rate down to a level that a 60hz LCD or picture tube could display.

Construction

To build the triple helix, I used a 1/2" clear, acrylic rod for the center and similar 1/8" rods sticking out of the side to support the screen. To make a drill template for the support dowels, I cut a piece of paper with a horizontal size of the 1/2" dowel's circumference and a vertical height of 4 and 1/4", divided it by three, and drew lines from the lower-left edge to the upper-right edge of each section, putting a hole mark at each edge. Then, I simply wove fishing line between the supports. I did this because the supports are non-planar.

The result is a semi-transparent screen. Internal reflection provides a means of showing the scene to all viewers regadles of angle.

For the protective box that contains this screen, I used spare pieces of the 1/2" dowel rod to be placed vertically at the corners of two pieces of plexi-glass, one at the top and one at the bottom. Each Piece of plexi-glass must have a 1 1/8" hole in the center in which to place a race bearing connected to the heliis' dowel rod. The upper piece will also need a place for a drive motor.

The projector setup involves an LCD and overhead, or it could contain picture tubes from a projection television mounted separately on movable positioning equipment, a special lens with one convex side and one flat side, and both approaches require a computer animation to display the object.

The mount is composed of ten aluminum bars clamped together with the helix resting in the center square above the tv.

Necessary Materials

Screen

1.) 18-3 1/4" long 1/2" acrylic rods

2.) 1-6" long 1/8" acrylic rods

3.) Fishing Line

4.) 2 Race bearings with 1/2" holes

Box

5.) A drive motor

6.) 2-8"x8" pieces of plexi-glass

7.) 8 Small screws

Mount (If using a picture tube)

8.) One plano-convex lens

9.) 10 Aluminum bars

10.) 8 Aluminum clamps

Projection System

9.) At least one picture tube with a controller from a projection television or a 60hz LCD

10.) One Amiga 1200 playing an animation

Resources

1.) Blundell, B.G. and Schwarz, A.J., "Visualization of Complex System Dynamics on a

Volumetric 3D Device," University of Canterbury, New Zealand

2.) Benson, Harry, "Discover Magazine Awards," Copyright Discover Magazine 1996

3.) Daviss, Bennett, "Boob Cube," Copyright Discover Magazine 1996

4.) Chinnock, Chris, "Geek Page"

5.) Soltan, Parvis, "Volumetric Displays," (Original)

6.) Soltan, Parvis, "Laser-Based 3-d Volumetric Displays," (Second Generation)

7.) WU, Corinna, "A New 3-Dimentional Display Turns On the Imagination," Science News,

Vol. 150, pg. 270,271 Oct. 26, 1996

Proxima Corporation

9.) Unknown, "Edmund Scientific," Copyright Edmund

Scientific Corporation 1997

10.) Gregg Favalora@Actuality Systems

Latest Info

Development has halted, and I have moved on to other projects.

I am currently developing the system with an LCD on an overhead projector as a light source. I will be working out the timing.

Links

My IUPUI page with links to all my sites

If you know of any suggestions or questions, contact me at tvtronix@chilitech.com