WO2007064633A1

WO2007064633A1 - Virtual reality display system

Info

Publication number: WO2007064633A1
Application number: PCT/US2006/045525
Authority: WO
Inventors: Jason Leigh; Cristian Luciano; Andrew Johnson; Robert Kooima; Greg Dawe
Original assignee: The Board Of Trustees Of The University Of Illinois
Priority date: 2005-11-29
Filing date: 2006-11-28
Publication date: 2007-06-07

Abstract

One example system of the invention is a virtual reality system for displaying a viewer centered stereoscopic image. This example system comprises first and second displays arranged about an axis at an orientation angle of at least about 90° to one another. A polarizing filter is adjacent to each of the first and second displays. A half-mirror is arranged about the axis and approximately bisects the orientation angle. The half-mirror has a width and a height, at least one of which is at least 10% greater than a corresponding of the first and second display width and height.

Description

VIRTUAL REALITY DISPLAY SYSTEM

TECHNICAL FIELD

A field of the invention is virtual reality displays and systems.

An additional field of the invention is stereoscopic displays.

STATEMENT OF GOVERNMENT INTEREST

This invention was made with United States government support

under contract number CNS 0420477 awarded by the National Science

Foundation ("NSF"). The United States government has certain rights in the

invention.

BACKGROUND ART

Many current three-dimensional displays are based either on

imaging techniques that achieve an apparent stereo by perspective views or on

two presented images which are separated so that a viewer's right and left eyes

see their respective images which are differentiated by polarization

characteristics. Many of these displays are designed to view stereoscopic

images and/or images that offer a depth of field (e.g., three dimensional image).

Two images separated or distinguished by polarization are superimposed or may be displayed time sequentially to give an image which appears to be

continuous.

Stereoscopic and similar display systems that accomplish these

effects have been known for some time. One general configuration includes

first and second monitors disposed at an approximate right angle to one

another, with a half-mirror approximately bisecting the two monitors. The first

monitor provides a left eye image and the second provides the right eye image.

The angular polarized light transmitted from one monitor is flipped when a

viewer views the image as reflected by the half-mirror, while the angular

polarized light from the second monitor remains in its original state when

viewed by the user through the non-reflecting portion of the half mirror. One

image thereby arrives at the user with one polarization and the second with a

different polarization. If the user wears glasses with different filters for each

eye, the two different polarizations can be resolved whereby the user observes

distinct left and right eye images. A perception of depth is thereby achieved.

This basic configuration has been used for some time, with many

improvements proposed from time to time. United States Patent No. 2,845,618

discloses an early example of such a device, while United States Patent No.

6,703,988 discloses an example of a much more recent improvement. In

addition to these disclosures, a number of additional display systems have been

proposed with the goal of improved displays.

For example, when plasma screen technology became available

they were used to generate field-sequential stereo. In practice, however, plasma screens were found to be difficult to incorporate in such systems. They

were electromagnetically noisy making them incompatible with

electromagnetic trackers, which may be used in some applications including

virtual reality systems. Also, the displays refreshed at 60 Hz which meant that

the stereo images refreshed at a mere 30 Hz - resulting in considerable eye¬

strain for viewers. Also, the red and green phosphors did not decay as quickly

as the blue resulting in considerable cross-talk in the left and right-eye images.

A number of additional recently developed systems are

commercially available. Auto-stereoscopic displays have recently been

marketed to take advantage of the low cost of LCD monitors. While these

displays are suitable for viewing stereoscopic images, they are not well suited

for viewing viewer-centered stereoscopic images because they require that the

viewer keep their head stationary and straight in order to see the correct pairs of

vertically interleaved images. Furthermore, many of these displays achieve a

maximum effective resolution of only about 800 x 1200 pixels. Finally,

displays used in these systems tend to be relatively small.

To attempt to address some of the current limitations of

autostereo displays, a barrier-strip autostereo display was developed that uses a

moving virtual line screen synchronized with viewer-centered perspective to

enable a viewer to move their head and to tilt it slightly during viewing. While

successful, 3/4 of the screen's native resolution is used to reduce moire effects

since 4 pixels are rendered for each anti-aliased stereo pixel. Furthermore, precise low-latency head tracking is needed to ensure that the stereo images are

perfectly aligned with the viewer at all times.

Other problems in the art related to incompatibility with head

movement. Many current systems use linear polarizers to polarize one of both

of the display images, with a user wearing linear polarized glasses to resolve

the image. When the user tilts their head, however, stereo imaging is lost due

to the linear polarized glasses. Still other problems relate to the field of view of

stereo images. A limited field of view limits a user's movement to the left or

right, and further limits the ability of a single system to be viewed by multiple

users.

DISCLOSURE OF INVENTION

One example system of the invention is a virtual reality system

for displaying a stereoscopic image. This example system comprises first and

second displays arranged about an axis at an orientation angle of at least about

90° to one another. A polarizing filter is adjacent to each of the first and

second displays. A half-mirror is arranged about the axis and approximately

bisects the orientation angle. The half-mirror has a width and a height, at least

one of which is at least 10% greater than a corresponding of the first and

second display width and height. BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an example system of the invention;

FIG. 2 is a partial cutaway of a portion of a display of the system

of FIG. 1;

FIG. 3 schematically illustrates an aspect of an example system

of the invention;

FIGS. 4A-4D are schematics useful to illustrate some advantages

of example systems of the invention over prior art systems;

FIG. 5 illustrates a second example system of the invention;

FIG. 6 schematically illustrates a third example system of the

invention in an open position; and,

FIG. 7 schematically illustrates the example system of FIG. 6 in a

closed position.

BEST MODE FOR CARRYING OUT THE INVENTION

One example embodiment of the present invention is a desktop

virtual reality (VR) system that offers high-resolution, a wide range of view,

and high-visual-acuity passive-stereo visualization on a single-computer-driven

system. FIG. 1 is a schematic illustration of one example system 10. The

system 10 includes first and second displays 12 and 14 supported by an

adjustable frame 16 and oriented to one another at an angle θ. The frame 16

was built using extruded aluminum parts, and allows for adjustment of the

angle θ by pivotal adjustment about an axis A. The angle θ may be adjusted as desired, but will generally be greater than 90° and less than about 140°. Larger

angles may be useful in some applications.

Any number of different displays 12 and 14 will be suitable for

practice of the invention. In many systems, beneficial results can be obtained

through use of relatively large and high resolution displays. Some example

monitors useful in invention embodiments are at least 30 in. monitors, others

are at least 32 in., and still others are at least 40 in. It will be appreciated that

when discussing displays herein, the use of dimensions unless expressly noted

otherwise will refer to the standard diagonal screen measurement used in

industry. By way of example, reference to a "32 in. monitor" will be

understood to be reference to a monitor having a diagonal measurement of 32

in.

In the example system 10 the monitors are 30 in. Apple Cinema

Displays from APPLE CORP., California, United States. One benefit of using

relatively large monitors, with an example being at least 30 in. size, is viewing

angle. Given that the 30 in. screen is 25 in. wide in the horizontal direction,

when viewed from a comfortable distance (with an example being

approximately 24 inches) the user's field of view is about atan (25/2 x 1/24) x 2

= 55°. Given that the visual acuity of a display can be computed as

20/(FOV*1200/resolution), therefore, the visual acuity of the example system

10 is about 20/(55° x 1200/2560), which is approximately 20/26.

Use of widely commercially available monitors may be beneficial

for cost, reliability, interoperability, and other reasons. In addition to the Apple Cinema Displays, other suitable commercial displays include the NEC

Mitsubishi Multisync LCD4010-BK 40" LCD display form NEC

MITSUBISHI (Japan), the Mitsubishi MDT461S 46" LCD display from

MITSUBISHI (Japan), JVC GM-H40L2GU 40" LCD display from JVC

(Japan), ViewSonic N3751w 37" LCD display from Viewsonic Corp. (USA),

and others. One advantage of using LCD displays 12 and 14 is there relatively

high level of brightness. This allows them to be readily used under normal

office and other lighting environments.

Displays 12 and 14 of the invention also preferably achieve a

high resolution not available in the prior art. The example Apple Cinema 30 in.

displays have a resolution of 2560 x 1600 pixels (i.e., greater than 4 mega pixel

total resolution). Other systems of the invention will utilize other displays to

achieve even greater resolution. One example is the IBM T221-DG5 QUXGA-

W 22.2 in. LCD display from IBM Corp. (New York, USA). This display

provides a resolution of 3840 x 2400 pixels (i.e., greater than 9 mega pixel total

resolution). These levels of resolution are not available in systems of the prior

art, and will be of particular value in many applications where great image

detail is desired. Relatively large displays are one example of an application

for which enhanced resolution will be of significant benefit.

To achieve even greater resolution, other example embodiments

of the invention replace each of the displays 12 and 14 with a plurality of

displays in a tiled configuration. For example, replacing the displays 12 and 14

with a set of 4 IBM T221-DG5 QUXGA-W 22.2 in. LCD displays would result in each display 12 and 14 having a total size of about 45 in. and a total

resolution of over 36 megapixel. Arrangements of 4 x 4 tiled displays, 4 x 6

tiled displays, 6 x 6 tiled displays, and 6 x 8 tiled displays are contemplated.

Many other tiled configurations are possible and will be apparent to those

knowledgeable in the art. Software or other means may be provided to split an

image across the plurality of tiled displays to result in a single composite

image. LCD displays also offer an advantage in their elimination of flicker.

Many systems of the prior art that use cathode ray tube screens, by way of

example, are subject to some degree of flicker due to the use of an electron gun

scanning across the screen to produce an image.

A half mirror 18 is arranged between the displays 12 and 14

about the axis A and approximately bisects the angle θ. The term "half mirror"

will be understood by those knowledgeable in the art. As used herein it is

intended to be broadly interpreted as any media which has one substantially

reflecting surface and an opposite surface that is substantially transmissive. An

example of a half mirror 18 is one in which one surface is only partially

covered with silver reflecting media, with an example being about 50% or 60%

coverage. In the example system 10, a 6 mm half-silvered glass mirror with

40% refractivity and 60% reflectivity was used (often referred to as a "40/60"

coating). Other half mirrors will likewise be suitable.

A thinner mirror, for instance, may be used, but it has been

discovered that when using larger half mirrors useful with large displays,

greater thicknesses are desirable to add strength and rigidity. A thickness of at least about 6 mm is one example thickness believed to be useful, while in other

systems a thickness of at least about 8 mm may be useful. A polarization-

preserving half-silvered acrylic mirror is another example half mirror that will

be useful in practice of the invention. The half mirror 18 is arranged with its

reflective surface 20 oriented to face the uppermost display 12.

In operation, a user that views the half mirror 18 will observe an

image displayed by the display 12 reflected from the mirror's reflecting surface

20 superimposed with a second image displayed by the display 14 that is

transmitted through the reflecting mirror's non-reflective surface opposite from

the reflective surface 20. If the two displays 12 and 14 simultaneously show

cooperating stereoscopic images (e.g., left and right eye imagery), stereoscopic

viewing can result. By way of example, if the display 12 is displaying an

image recorded from a left eye perspective while the display 14 shows an

image recorded from a right eye perspective, a viewer will observe stereoscopic

imagery including one with three-dimensional depth.

In order to accomplish this, however, a user must resolve the left

and the right eye imagery. Put another way, the user must be able to view the

image originating from the display 12 and from the display 14 with different

eyes. This can be accomplished in several different manners, using different

structural configurations. The example system 10 is configured to deliver

images from each of the displays 12 and 14 with different polarizations, and

then "decode" the different polarizations when they arrive at the user for

viewing by different eyes. Polarization is accomplished using polarizing filters 22 that cover

each of the displays 12 and 14. Since the light from large LCD screens is

polarized vertically, the addition of the quarter-wave plate creates circularly

polarized light. While the light passing through the half-silvered mirror is

polarized in one circular direction, the light from the top LCD screen reflecting

on the mirror is polarized in the opposite direction. A viewer wears a pair of

circularly polarized glasses to resolve the stereo image.

FIG. 2 shows a portion of each of the displays 12 or 14 in partial

cutaway. The filter 22 substantially overlies the screen 24 of each of the

displays 12 and 14. The filter 22 has been laminated between two transparent

acrylic sheets 26 for rigidity. Although different polarizing filters 22 are

suitable for use with different example systems of the invention, with examples

being linear or circular polarizers, the filter 22 is a quarter- wave plate with the

fast axis oriented at 45 degrees. The filter 22 has been laminated between two

polarization-preserving acrylic sheets 26 for rigidity and then attached to the

display 12/14. The filter 22 is substantially coextensive with the LCD screen

24. The filter 22, acrylic sheets 26 and screen 24 may be attached to one

another using adhesive, mechanical fasteners, or the like.

In the example system 10, the filter 22 was obtained from the

American Polarizer Corp., Reading Pennsylvania, United States. It is an

Acrylic Laminated Quarterwave Retarder with retardance of 140 nm and its

fast axis at 45 degrees. Its dimensions are 18 in. x 27 in. x 0.070 in. thick. Other retardances, fast axis orientation, and dimensions will be useful with

other invention embodiments.

The use of the quarter wave plate 22 to achieve circular

polarization has been discovered to be particularly well suited for use with

liquid crystal display (LCD) displays that are larger than about 17 in. (or in

some cases larger than about 19 in.). LCD screens smaller than about 17 in. (or

in some cases about 19 in.) emit linear polarized light at a 45 degree angle.

Larger LCD screens, however, emit linear polarized light at zero degrees.

Linearly polarized light at 45 degrees when reflected off a mirror will produce

linearly polarized light at 45 degrees. However, light polarized in a vertical

angle will still produce polarized light at zero degrees when reflected. As a

result, it has been discovered that light emitted from LCDs that are larger than

about 17 in. (or in some cases 19 in.) cannot rely on linear polarizers. It has

been discovered that a useful means to create oppositely polarized light is

through circular polarization. The quarter-wave plate 22 that converts linearly

polarized light to circular polarized light has been discovered to be effective.

Light from the display screen 24 of either of the displays 12 or 14

will exit the quarter wave plate or filter 22 with a circular polarization. When

the circular polarized light from the upper display 12 reflects off of the

reflective surface 20, it "flips" polarization. That is, it reverses its rotational

direction. The circularly polarized light from the lower display 14, however,

doesn't undergo any change as it passes through the non-reflective surface of

the mirror 16. As a result, images from the displays 12 and 14 will arrive from the mirror 18 to the user in different circular polarizations phases: a first phase

from the lower display 14 that is not reversed by the mirror 18 and a second

image from the top display 14 whose polarization undergoes reversal at the

mirror 18.

The user is required to resolve these different polarizations. In

the example system 10, this is accomplished through use of wearable glasses

30. The glasses 30 include two lenses 32 and 34, each of which are a circular

polarization filter that are oriented in an opposite direction of one another. The

lens 32 and 34 are composed of a right-circular polarized and a left-circular

polarized filter. Accordingly, one lens 32 will resolve the image originating

from the display 12 and the other lens 34 will resolve the image from the

display 14. In this manner, the user views stereoscopic imagery.

Many systems of the prior art rely on the 45 degree polarization

that is naturally emitted from smaller (with an example being less than 17-inch)

LCD screens. This polarization is therefore reversed by a reflective surface so

a user can wear linear polarized glasses to resolve the stereo. In the case of

larger displays such as those contemplated for use with the present invention

(and others that do not emit 45 degree polarized light), however, it has been

discovered that linear polarizing filters will not provide the required separation

of display images, since larger LCD screens emit linearly polarized light in the

vertical direction (rather than at 45 degrees). The reflection of light polarized

in the vertical direction from a reflective surface such as the mirror 18 will not

re-orient the light at 90 degrees. Accordingly, displays that transmit vertically polarized light (with an example being LCD displays that are larger than 17 in.)

used with linear polarizing filters will result in the images from each of the

displays arriving at the user with the same polarization. No resolution to

separate the two images is thereby possible, at least through polarization

techniques.

In addition to allowing use of displays that transmit linear

polarized light (such as displays 12 and 14), the circular polarizing filters 22

provide other advantages as well. For example, use of circular polarization has

been discovered to provide superior performance over linear polarization for

allowing movement of a user's head relative to the system 10. Put another

way, use of circular polarization has been discovered to provide increased

freedom of movement of a user's head while maintaining stereo when

compared to linear polarization. Users are able to tilt their head sideways while

still resolving two different images to each of their eyes. This is not possible

with linearly polarized stereo of the prior art.

Referring now to the schematic of FIG. 3 by way of illustration,

as a user U tilts her head in the general direction of either of arrows A away

from a vertical axis V when using a system that relies on linear polarization,

stereo is lost. This occurs since the orientation of the linear polarization filter

on the user glasses is critical to resolving the linear polarized light coming from

the system S. This critical dependence on orientation, however, does not exist

for circularly polarized light — the angle of orientation of a circular filter does

not affect its ability to filter circularly polarized light. This provides a system of the invention such as system 10 that

uses circular polarized filters important benefits and advantages over systems

of the prior art that relied on linear polarized filters, including an increased

tolerance for user movement. These benefits and advantages may be of

particular value in applications such as virtual reality simulations, gaming and

the like where users are expected to move their heads (including tilting

movement) in response to changing imagery.

It is also noted, however, that in some applications this increased

field of user movement may not be necessary, and that in such applications

linear polarizing filters will be suitable for practice of the invention. In many

applications, however, an increased field of user view will provide very

valuable benefits and advantages. In addition to the above examples, other

applications will also benefit from an increased field of user view. One

additional example is large scale displays that may be viewed by multiple users

simultaneously. Examples include engineering, satellite and map imagery,

astronomy, geology, gaming, entertainment, and other applications in which

multiple users may wish to collaboratively view a stereoscopic image

simultaneously. Systems of the prior art have offered a limited ability to

achieve a suitable field of user vision for accommodating many of these multi-

user applications.

An additional aspect of the present invention has been discovered

to offer particular utility for addressing these unresolved needs. In particular,

some example systems of the invention include a mirror that is significantly larger than either of the displays. Referring again to FIG. 1, the half-mirror 18

has a horizontal width X_M that is wider than the horizontal width X_D of either

display 12 or 14 (in most, but not all, applications, the dimensions of the

displays 12 and 14 will be identical). The half-mirror 18 also has a vertical

height Y_M that is larger than the height Y_D of either display 12 or 14.

It has been discovered that providing a mirror 18 having a larger

width X_M (and/or height YM) than that of the displays 12 or 14 provides a

significant improvement over systems of the prior art that utilize a mirror

having substantially the same dimensions as the displays. These advantages

can be best illustrated through consideration of the schematics of FIGS. 4A and

4B. FIG. 4 A illustrates a user viewing a system of the prior art S_OLD which

includes a mirror M having a width X_M and height Y_M that are substantially the

same as the width X_D and height Y_D of each of the system's displays D. As

shown, when a user is located off center from the system and views the mirror

from an angle (as opposed from viewing it directly from center), only a limited

field of view having a width F is available on each of the displays D. This may

be further illustrated through the simplified schematic of FIG. 4B representing

a user U viewing a display D through mirror M to achieve a field of view

across the display D of F. FIG. 4B also schematically illustrates a viewing

zone VZl in which a user must be in order to see the full width of the display

D.

FIGS. 4C and 4D contrast the prior art system S_OLD with

schematics illustrating an example system S_NEw of the present invention, with the user U positioned at the same position as she was in FIGS. 4A and 4B.

Referring now to FIG. 4C, in the system S_NEw the mirror M has a width X_M and

height Y_M that are substantially larger than the width X_D and height Y_D of

either display D. As shown, the wider mirror allows for a user to enjoy a much

larger width of field of view F on the displays D when the user views the

system from off center. This is further illustrated through the simplified

schematic of FIG. 4D showing user U viewing display D through a mirror M

that is wider than the display D and thereby achieves an enhanced width of

image F on display D. FIG. 4D also illustrates a viewing zone VZ₂ in which a

user may observe the full width of the display D. As illustrated, the viewing

zone VZ₂ is significantly larger (in the horizontal direction) than is the zone

VZ₁ of FIG. 4B.

Although not illustrated by FIGS. 4A-4D, it will be appreciated

that in addition to achieving a wider field of view F, mirrors that have a larger

height Y_M than the display height Y_D will likewise achieve an increased field of

view in the vertical direction as a user views the mirror from a position that is

vertically off center.

The degree of size difference between the mirror width and

height and that of the display will vary with application. Generally, as the

mirror size increases the distance that a user can move off-center while

continuing to observe a full screen increases. These benefits must be balanced,

however, against inconveniences that arise from a mirror that is overly large

and bulky. It is believed that in many applications, a useful balance is achieved through use of mirrors that have a width X_M at least about 10% greater than the

display width X_D. In other systems the mirror width X_M is at least about 20%

wider, in others at least about 25% wider, and in others width X_M is at least

about 30% wider, and in still others it is at least about 40% wider. In some

systems of the invention the mirror height Y_M will be at least about 10%

greater than display height Yp, in others height Y_M is at least about 20%

greater, and in others height Y_M is at least about 30% greater.

Those knowledgeable in the art will be able to appreciate the

valuable gain achieved in field of view through these increased widths.

Straightforward geometrical calculations can be made, for example, using the

schematics of FIGS. 4 A-D to show the increased field of view (VZ₁ of FIG.

4B) for a user at a given distance from the display.

It is believed that in many applications, including those in which

multiple users crowd around a system to view the same image simultaneously,

an increase in width X_M may be more beneficial than an increase in height Y_M.

Accordingly, in one system of the invention the mirror width X_M is at least

about 20% greater than the display width X_D, while the mirror height Y_M is

between about 10% and 20% greater than the display height Y_D.

The mirror 18 that is larger than either of the displays 12 and 14

provides unexpected benefits, as described herein above. It is believed that

systems of the prior art relied on mirrors that were the same size as their

displays for many reasons. For one, the larger mirror 18 of the present

invention presents a larger footprint for the system 10 that requires additional space and presents other challenges over systems of the prior art that use a

smaller mirror. It is suspected that these factors may have prevented others

from modifying systems of the prior art. It has been discovered, however, that

these factors are significantly outweighed by the benefits and advantages that

the larger mirrors of the present invention provide.

Having now provided a discussion of structural and operational

aspects of example systems of the invention with respect to viewing images,

further detail is appropriate regarding control of systems of the invention and

generation of images on the displays 12 and 14. Operation of the system 10 is

controlled by a controller 40, which may be, for example, a processor based

device such as a computer. It may include one or more processors, a memory,

multiple ports for inputting and outputting data and signals, and other

components that are generally know.

The controller may further include one or more hardware and

software components for operating the system 10, with examples including

software components for generating and/or processing left and right eye image

data to be displayed on displays 12 and 14, software drivers and hardware

components for operating the displays 12 and 14, and the like. Specialized

hardware and software for driving displays and for generating image data are

widely commercially available, with examples including display drivers

available from manufactures (including APPLE Corp., California, United

States) and specialized graphics processors. The system 10 is contemplated as being a passive system,

(although other systems of the invention could be active), meaning that the

controller 40 displays left and right eye images simultaneously and relies on the

user to resolve them. The left and right eye images displayed on the displays

12 and 14 may comprise still images, sequential images, continuously moving

images (e.g., movies), and combinations thereof. Examples include two and

three dimensional engineering drawings, movies, computer generated graphics,

maps, satellite imagery, and the like. The controller 40 may utilize standard

stereo off-axis projection calculations to generate viewer-centered perspective,

even in response to movement of a user's head position or orientation.

The controller 40 in the example system 10 utilizes a commercial

graphics card with two dual-link DVI outputs, such as the nVidia Quadro FX

4400 available from NVIDIA Corp., California USA. Other suitable

components include two nVidia Quadro FX 3400 synchronized by a SLI

connector. This latter alternative required a powerful power supply to drive

both cards. In addition, it allowed for full resolution on both displays, but not

in clone mode. As a result, the former component may be desirable in many

applications over the latter. Many other commercial graphics cards are useful

in practice of the invention, including those that are suitable to display at the

maximum resolution on both LCD displays 12 and 14 when operated in clone

mode.

In the example system 10, the controller 40 is configured to

address the need to flip the image displayed on the top display 12 so that the image reflected from mirror 18 does not appear reversed. This is accomplished

through a software component operating on the controller 40. Although

commercially available drivers such as nVidia ForceWare stereo drivers

(version 77.77 available from NVIDIA Corp., California United States) allow

applications showing full-screen clone-mode stereo to flip the orientation of

one of the images, it has been discovered that these are not appropriate for

some applications of the present invention. Although these drivers allow fixed-

viewpoint applications such as DirectX games or OpenGL CAD applications to

work in stereo without any modification, they cannot be used for viewer-

centered perspective because the driver does not support user head position and

orientation tracking. Instead, these drivers assume a fixed head position with

horizontal eye alignment and a constant inter-ocular distance making them

unable to achieve some of the benefits of the system 10.

The present invention includes a more general method for

implementing viewer-centered perspective through operation of the controller

40. A software program operating on controller 40 achieves this. In particular,

the projection matrix for an image is vertically flipped by swapping the top and

bottom parameters used to specify the projection. In OpenGL software code,

for example, this amounts to swapping the 3rd and 4th parameters to

"glFrustum" or "glOrtho." Those skilled in the art will appreciate that other

commands will be useful to achieve this when using other programming

languages. It has also been discovered, however, that flipping the projection

in this manner has a side effect that must be corrected. For example, it results

in the reversal of the winding of all polygons. In computer graphics, back-face

culling is often used to determine whether a polygon of a graphical object is

visible depending on the orientation of the camera. Back-face culling

commonly uses winding to distinguish back from front facing polygons, thus a

flipped projection will invert the effect of the back- face culling mechanism. In

OpenGL code, the front-face winding can be reversed with a call to

glFrontFace(GL_CW) prior to the rendering of the flipped view. Those skilled

in the art will appreciate that other commands will be useful to achieve this

when using other programming languages.

Depending on the installed orientation of the displays, the flip

may be either vertical or horizontal. A horizontal flip behaves just as a vertical

flip, but requires the swapping of the left and right projection parameters. The

polygon rewinding requirement remains the same. In the event that both a

horizontal and a vertical flip is necessary, no polygon rewinding is necessary,

as the rewindings of the flips cancel out. A generalized display configuration

mechanism should include flags to enable a horizontal or vertical projection

swap, and should enable polygon rewinding on the exclusive-or of these flags.

One example system of the invention includes a software component that uses

such a mechanism.

The controller 40 may also be linked to the frame 16 for

controlling the angle θ as well as the position of the bisecting mirror 18. In particular, the frame 16 may include a pivoting gear drive 42 connected to the

display 12 and a pivoting gear drive 44 connected to the mirror 16. Each gear

drive 42 and 44 is linked to the controller 40, which is configured to operate

each of the drives. Through their operation, the controller 40 may alter the

angle θ and/or the position of the bisecting mirror 18. This can be useful and

convenient when different sized users or different numbers of users, for

example, use the system 10.

The example system 10 further includes a tracking system

connected to the controller 40. Tracking systems are generally known in the

art, and detailed description herein is therefore not necessary and will not be

provided for sake of brevity. The tracking system is useful to track motion and

orientation of one or more user's position, including their head and one or both

hands. The tracking system may determine one or more of position, tilt and

rotation. Many commercially available tracking systems are suitable for use

with the system 10, with one example being the FLOCK OF BIRDS system

from ASCENSION TECHNOLOGY CORP., Burlington, Vermont, USA.

The example tracking system shown in FIG. 1 is wireless, and

includes a locator 50 and a plurality of sensors 52. One or more sensors 52 are

held on the glasses 30, and one sensor 52 in on a hand held interaction device

54 which may be configured, for example, for wearing on a user wrist or hand.

Other example systems of the invention may use glove sensors which respond

to movement of a user's hand such as gripping motion, twisting, individual

finger movements, and the like. The locator 50 is configured to determine the location and orientation of each of the sensors 52 in three dimensional space

through any of various technologies, with an example being light (such as

infrared), sound, electrical signal, and the like. The example system 10 uses a

tracking system that employs DC magnetic technology, which has the

advantage of not requiring a line of sight between locator 50 and sensors 52.

The locator 50 is linked to the controller 40 which is configured

to operate the tracking system and to process data provided by it. As a user's

hands and head move about with sensors 52 attached thereto, their movements

and positions are tracked. As a user tilts or turns his head, the position and

orientation of the sensor 52 on the glasses 30 can be used to determine head

position and orientation, including tilt and/or rotation. An absolute distance

between the user's head and the mirror 18 can be determined, as well as a

distance for each particular of the user's two eyes.

The controller 40 can use this data to change the user perspective

and other aspects of the left and right eye images being displayed on the

displays 12 and 14 to maintain stereo imagery for the user. Further, the

controller 40 can manage virtual objects that are displayed by one or more of

the displays 12 and 14 that can be "touched" and otherwise manipulated by a

user. The controller 40 can determine when a user's hand (with a bracelet with

a sensor 52 attached) has moved into a location where the user "sees" a virtual

object. The virtual object may be moved or other actions may be taken in

response to further detected movements by a user. In operation the tracking system may require initial calibration.

For example, the controller 40 may provide test screens and request specific

movements by a user to specified locations to calibrate itself. Although the

tracking system of the system 10 has been illustrated as being suitable for use

by one user, other example systems of the invention may include multiple

passive users wearing polarized glasses to observe the stereo images, or may

include multiple interaction devices for simultaneous use by the multiple users.

The present invention also contemplates controlling the system

10 through manipulation by a user of virtual objects displayed on the displays

12 and 14. Virtual buttons, knobs, switches and the like may be displayed, and

operated through manipulation by a user's hand and head movements that are

detected by the locator 50 and controller 40. In some systems of the invention,

for example, the angle θ can be controlled through such operation. A user

desiring to change the angle θ might manipulate virtual knobs and dials, with

the controller 40 operating the gear drive 42 in response.

It will be appreciated that the system 10 is but one example of a

system of the invention. Many alterations, equivalents, and modifications may

be made without departing from the scope of the invention as claimed below.

By way of example, FIG. 5 illustrates a second example system 110 of the

invention that has been configured for positioning on a tabletop. The system

110 is similar in many respects to the system 10, and like element numbers will

be used in the 100 series for convenience and clarity. The system 110 is configured for desktop use, and includes

displays 112 and 114 supported by frame 116 and positioned at a 90° angle to

one another. The displays 112 and 114 are 19 in. LCD displays emitting linear

polarized light. Each is fitted with a quarter wave plate for producing circular

polarized light. A 40/60 half mirror 118 approximately bisects the displays 112

and 114. The mirror 118 has a width that is substantially wider than the

displays 112 and 114. A processor based controller 140 is generally consistent

with the controller 40 described above, and processes left and right eye images,

communicates them to the two displays 112 and 114, and otherwise controls

operation of the displays 112 and 114. The controller 140 is linked to each of

the displays 112 and 114.

The frame 116 is configured in a different manner than the frame

16 of FIG. 1. The frame 116 may be made of suitable materials selected for

strength and rigidity while maintaining a relatively low weight and cost.

Example materials of construction include metals such as aluminum, steel

alloys, and even rigid plastic. The materials should be compatible with the

system 110 - steel is not appropriate if using an electromagnetic tracking

system. The frame 116 includes an overhead rack 160 to which an upper

display 114 is mounted. The frame 116 further includes a generally U-shaped

base 162 that sits on the tabletop. First and second posts 164 connect the

overhead rack 160 to the base 162. Cross members 166 connect the posts 164

to the overhead rack 160, and also are pivotally connected to the mirror 118. An adjustable support 168 connects the base to the mirror 118 at

each of its side. The length of the support 168 may be adjusted to cause the

mirror 118 to pivotally move relative to the cross members 166 and thereby

change its angle of orientation relative to the user U. The support 168 may

comprise, for example, an adjustable piston, or cooperating telescoping arms

with an internal gear drive for adjusting length. The support 168 may be linked

to the controller 140 for automated adjustment.

The user U using the system 110 is wearing glasses 130 that are

equipped with two quarter wave plates set in the same phase to resolve the left

and right images the user views from the mirror 118. The system 110 also

includes a tracking system. Unlike the tracking system of the system 10,

however, the tracking system of the system 110 is not wireless - it is connected

by a wire 170 to the system 110. The tracking system includes a sensor

attached to the glasses 130 for tracking the user's head position and orientation.

The user U may also provide input to the controller 140 through hand

movement, with examples including a hand mounted sensor, a mouse wired to

the controller 140, a keyboard, or other device(s).

FIGS. 6-7 illustrate still an additional system 210 of the

invention. The system 210 shares many common components with the systems

10 and 110, and like element numbers have been used in the 200 series for

clarity and convenience. For sake of brevity, description will not be provided

herein concerning elements of the system 210 that are consistent with those of

systems 10 or 110, and description of those systems may be had through the above provided discussion. By way of example, the displays 212 and 214 and

mirror 218 are generally consistent with those suitable for use with the systems

10 and 110. The mirror 218, for example, is at least 10%, and may be at least

20%. 30% or 40% wider than the displays 212 and 214, and likewise may have

a height that is at least 10% or at least about 20%, 30% or 40% greater than the

height of the displays 212 and 214.

Additionally, the displays 212 and 214 are liquid crystal displays

that emit linearly polarized light, and include circular polarizing light filters.

They may be at least about 20 in., at least about 30 in., or at least about 40 in.

in diameter. The displays 212 and 214 may have a resolution of at least about

4 megapixels, or of at least about 9 mega pixels. Some elements of the system

210 are different from the system 10 and 110, however. Discussion of these

elements is provided below.

The system 210 is configured for portability, and includes a

collapsible or foldable frame 216. The collapsible frame is shown generally at

216, and includes a base 302 and a base support arm 304 that is pivotally

connected to the base 302 at a first end 306. A second support arm end 308 is

connected to a gear mechanism shown generally at 310 that includes first and

second gears 312 and 314 that are rotatably engaged with one another whereby

rotation of one cases rotation of the second. The two gears 312 and 314 each

rotate about an axial hub 315 which is mounted on a connecting arm 316. The

rotatable gear 312 includes a connector 318 that connects it to the base support

arm 304, and the rotatable gear 318 includes a second connector 318 that connects it to a top support arm 320. The connectors 318 are fixedly connected

to the gears 312 and 314, so that they rotate with the gears. The top support

arm 320 supports the upper display 212 near a first end, and a counterweight

322 is connected to a distal second end. A half mirror 218 is connected at

approximately a right angle to the connecting arm 316. The half mirror 218

bisects the angle θ that the displays are oriented to one another at.

The frame 216 is collapsible. As used herein in this context, the

term "collapsible" is intended to be broadly interpreted as meaning foldable or

the like. FIG. 7 illustrates the system 210 in a closed or folded position. The

base support arm 304 may be pivotally folded between its upright position

(FIG. 6) and its closed horizontal position (FIG. 7). The support arm 304

include a peg 324 that rides in a slot 326 cut in a guide bracket 328 that is on

the base 302. The slot 326 may include notches at its two ends for locking

engagement of the support arm peg 324. The guide bracket 328 further

rotatably holds a base support arm pin 330 about which the arm 304 pivotally

rotates. The slot 326 limits travel of the support arm 304, and provides locking

engagement to hold the arm 304 in its open upright position (FIG. 6). The base

302 may be configured in a general U-shape (when viewed from above) or

other configuration to provide stability on a tabletop or the like.

Once the base support arm 304 is in a locked upright position

(FIG. 6), the top display 212 may be pivotally moved into position. The gear

mechanism 310 allow pivotal movement of the upper support arm 320.

Importantly, as the upper support arm 320 is pivotally moved, the gear mechanism 310 maintains the half mirror 218 in a bisecting position between

the displays 212 and 214. This is accomplished through operation of the

rotating gears 312 and 314 together with the connecting arm 316. As the base

support arm 304 pivots upward and the gears 312 and 314 rotate, the half

mirror 218 that is rigidly connected to the connecting arm 316 at about a 90

degree orientation remains in a desired bisecting position. The top display 212

and bottom display 214, however, change position relative to the gear

mechanism 310 since the connectors 318 rotate with the gears 312 and 314.

The gear mechanism 310 is lockable, so that when the lower

support arm 304 is in a locked upright position the gear mechanism 310 may

likewise be locked to hold the position of the display 212 and mirror 218. An

example locking mechanism includes the pin latch 332 which is effective to

prevent the gears 312 and 314 from rotating. Many other locking mechanisms

are contemplated for use with the invention, including cams, pins, levers and

the like. The gear mechanism 310 also allows for adjustment relative to the

base support arm 304 when it is in a locked position. This allows for the

position of the top display 212 and mirror 218 to be adjusted relative to the

lower display 214 as desired. This may be useful, for example, to adjust the

position of the upper display 212 and mirror 218 to accommodate a taller or a

shorter user.

The counterweight 322 eases the pivoting adjustment of the top

support arm 320, as does the connection of the upper support arm 320 to the

gear mechanism near its midpoint 334. These elements likewise have been discovered to be beneficial in maintaining the center of gravity of the system

210 centered over the base 302. The counterweight 322 has also been

discovered to provide a useful adjustment mechanism - it may changed as

desired to balance the top support arm 320 (and to shift the center of gravity of

the system 210) in response to use of a heavier or lighter top display 212. The

system 210 also includes cushions 336 that are useful to cushion the displays

212, 214 and mirror 218 when the system is in a closed, folded position (FIG.

7).

It will be appreciated that the system 210 may also include other

elements. For example, a case (not illustrate) may be provided for ease of

transport. A controller is also contemplated, which may be, for example, a

stand alone portable computer (not illustrated) that can be connected to the

displays 212 and 214 for driving the system 210. Tracking system components

can also be provided and connected to the controller, with examples including

the glasses 30, bracelets 54, locator 50 and sensors 52 of FIG. 1 for tracking a

user's head movement and orientation, and hand movement. Further structural

elements of the frame 216 can be provided, with examples including additional

adjustable supports for easing pivoting movement and further stabilizing the

top and bottom supports 304 and 320. Examples include one or more

adjustable gas shocks connecting the two supports 304 and 320 to one another

and/or to the base 302.

The above discussion and attached FIGS, describe example

systems of the invention. It will be appreciated that these are examples only, and that other systems of the invention may be configured in other ways, may

include additional or fewer components, and may be configured in different

ways. The above discussion is not intended to limit the scope of the invention

as claimed below, and descriptions of various system elements and components

are intended to be given their broadest possible interpretation.

Claims

CLAIMS:

1. A virtual reality system comprising:

first and second displays arranged about an axis at an orientation

angle of at least about 90° to one another;

a polarizing filter adjacent to each of said first and second

displays; and,

a half-mirror arranged about said axis and approximately

bisecting said orientation angle, said half-mirror having a width and a height, at

least one of said width and said height at least about 10% greater than a

corresponding of said first and second display width and height.

2. A virtual reality system as defined by claim 1 wherein said

half mirror has a width at least about 10% greater than said first and second

display width, and wherein each of said first and second displays have identical

height and widths.

3. A virtual reality system as defined by claim 1 wherein said

half mirror has a width at least about 30% greater than said first and second

display width.

4. A virtual reality system as defined by claim 1 wherein said

half mirror has a width at least about 30% greater than said first and second display width, and a height at least about 10% greater than said first and second

display height.

5. A virtual reality system as defined by claim 1 wherein said

half mirror has a width at least about 20% greater than said first and second

display width, and a height at least about 10% greater than said first and second

display height, and wherein said polarizing filters are configured to provide

circular polarization.

6. A virtual reality system as defined by claim 1 wherein said

polarizing filters comprise circular polarizers configured to provide circular

polarization.

7. A virtual reality system as defined by claim 1 wherein said

polarizing filters comprise quarter wave plates.

8. A virtual reality system as defined by claim 1 wherein said

first and second displays comprise liquid crystal displays that emit linear

polarized light in a diagonal direction.

9. A virtual reality system as defined by claim 1 wherein said

first and second displays are each at least 30 in. diagonal LCD displays and

have a resolution of at least about 4 megapixels.

10. A virtual reality system as defined by claim 1 wherein said

first and second displays are LCD displays having a resolution of at least about

4 megapixels, and wherein said polarizing filters are configured to convert light

emitted from each of said displays to circular polarization.

11. A virtual reality system as defined by claim 1 wherein said

first and second displays each have a resolution of at least about 9 megapixels

and each emit linear polarized light, said polarizing filters configured to

convert said linear polarized light to circular polarization.

12. A virtual reality system as defined by claim 1 and further

comprising:

a controller linked to said first and second displays for processing

left and right eye image data and for causing said first and second displays to

display said left and right eye image data;

glasses with polarization filters configured to resolve said right

and left images; and,

wherein said first and second displays each comprise liquid

crystal displays having a diameter of at least about 30 in. and each have a

resolution of at least about 4 megapixels.

13. A virtual reality system as defined by claim 1 and further

comprising:

a controller linked to said first and second displays for processing

left and right eye image data and for causing said first and second displays to

display said left and right eye image data; and,

a tracking system for tracking position and orientation of a user's

head, said tracking system linked to said controller, said controller further

configured to respond to movement of said user's head by adjusting said left

and right images whereby said user continues to observe stereoscopic imagery

as said user head changes one or more of position and orientation.

14. A virtual reality system as defined by claim 1 and further

comprising:

a controller linked to said first and second displays for processing

left and right eye image data and for causing said first and second displays to

display said left and right eye image data; and,

a tracking system for tracking the position of a user's hand, said

tracking system linked to said controller, said controller further configured to

provide one or more virtual objects in said imagery, to track said hand position

to determine when a user manipulates said one or more virtual objects, and to

respond to said manipulation by changing said left and right imagery.

15. A virtual reality system as defined by claim 1 and further

comprising:

a controller linked to said first and second displays for processing

left and right eye image data and for causing said first and second displays to

display said left and right eye image data; and,

a frame supporting said first and second displays and said half-

mirror, said frame adjustable whereby said angle between said first and second

displays may be changed, said frame linked to said controller and wherein said

controller is configured to cause said adjustment.

16. A virtual reality system as defined by claim 1 and further

comprising a collapsible frame supporting said first and second displays and

said half-mirror, said collapsible frame comprising:

a base;

a base support arm pivotally attached to said base and supporting

said first display;

a top support arm supporting said second display; and,

a gear mechanism adjustably linking said base support arm to

said top support arm ad configured to pivotally move said top support arm as

said base support arm is pivotally moved, said half mirror connected to said

gear mechanism, said gear mechanism configured to keep said half mirror at

said bisecting angle as said top and base support arms move.

17. A virtual reality system as defined by claim 16 wherein

said first and second displays comprise liquid crystal displays having a

diameter of at least about 30 in. and emitting linear polarized light, wherein

said half mirror has a width at least about 20% greater than said first and

second display width, and wherein said polarizing filters comprise quarter

wave plates configured to convert said linear polarized light to circular

polarization.

18. A passive virtual reality system for displaying a

stereoscopic image comprising:

first and second displays arranged about an axis at an angle of at

least about 90° to one another, said first and second displays being adjustable

about said axis relative to one another on said frame, said first and second

displays each having an identical width and height and a viewable diameter of

at least about 30 in., said first and second displays each transmitting linear

polarized light;

a quarter wave filter covering each of said first and second

displays and configured to provide said linear polarized light transmitted from

each of said first and second monitors with a circular polarization;

a half-mirror arranged about said axis and approximately

bisecting said angle, said half-mirror having a width at least about 20% greater

than said display width and a height that is at least about 10% greater than said

display height; glasses wearable by a user and including polarizing filters for

each of a left and a right eye;

a tracking system configured to track position of at least one

user's head and hand; and,

a controller linked to said first and second displays for processing

left and right eye image data and for causing said first and second displays to

display said left and right eye image data, said controller configured to generate

and image of a virtual object on said first and second displays, said controller

linked to said tracking system and configured to adjust said left and right

imagery to maintain stereoscopic imagery regardless of said user head position,

said controller configured to track motion of said user hand to determine when

said virtual object is being manipulated by said hand and to respond to said

manipulation by changing said left and right imagery.

19. A passive virtual reality system as defined by claim 18 and

further including a collapsible frame supporting said first and second displays

and said half mirror, said collapsible frame configured to maintain said half

mirror at said bisecting angle as said first and second displays are adjusted

about said axis relative to one another.

20. A passive virtual reality system as defined by claim 18

wherein said mirror has a width at least about 30% greater than said display width, and wherein each of said first and second displays have a resolution of

at least about 4 mega pixel.