# Patent

## Title
System for providing an enhanced immersive display environment

## Abstract

An immersive dome includes a number of novel features designed to enhance the performance of the immersive dome over presently-known immersive dome environments. Projectors are mounted in a multi-tier tower, out of sight beneath a viewing platform positioned to provide optimal wrap-around viewing. The projection surface consists of open-cell foam that allows passage of behind-surface sound into the dome while allowing unwanted ambient noise within the dome to escape. A visually-reflective coating, in conjunction with the open cell structure, provides a textured surface that acts as a micro-baffle and suppresses cross-reflection of projected imagery.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This Application claims priority to U.S. Provisional Application No. 61/258,974 filed Nov. 6, 2009, which is incorporated herein in its entirety by this reference thereto.


GOVERNMENT LICENSE RIGHTS
This invention was made with government support under contract no. FA9453-06-D-0103/0004, awarded by the United States Air Force. The government has certain rights in the invention.


BACKGROUND
1. Technical Field
The invention relates to immersive display of high-resolution imagery. More particularly, the invention relates to a system and method for providing an enhanced immersive display environment.
2. Description of Related Art
Immersive domes provide a visual environment offering seamless realism, wrapping imagery around the viewer's peripheral vision. These environments are useful for entertainment and for rapidly assimilating large amounts of visual information, such as in a command center.
Domes may have a single projector equipped with a fisheye lens or may integrate multiple projectors to provide higher resolution. In those domes equipped with multiple projectors, blending and warping software is typically used to give the impression of a single, seamless image. Although rear projection provides adequate resolution and coverage, it is impractical for large domes because interference from the dome support structure and excessive space requirements.
Several variations of immersive dome exist. In one well-known variation, the projector is placed in the plane of a canted auditorium floor. In another common variation, a cluster of projectors is hung from the top of the dome above the viewer. While the latter arrangement permits the viewer free movement on the floor below, it also blocks viewing of the portion of the dome directly overhead.
A disadvantage posed by the projection surfaces of immersive domes is that imagery projected on one portion of the surface can reflect onto another portion, causing visual interference such as washout. In essence, the spherical surface acts as an integrating sphere, diffusing light and lowering contrast.
Effective presentation of sound in an immersive environment is almost as important as presentation of visual information. However, domes present unique acoustic problems not encountered with flat or near-flat surfaces. For example, if the viewing surface is acoustically reflective, any sound made by viewers within the dome is reflected, causing echo and reverberation and impairing intelligibility. In fact, any sound within the dome, no matter the origin, may be cross-reflected, diffusing the origin point and thus reducing sound quality and directionality. Perforated domes attempt to alleviate this issue by allowing some sound to exit the surface to the outside, but much sound is still reflected. Additionally, the perforations can compromise screen reflectivity and, therefore, image brightness and may be visible to the viewer, especially on smaller domes with relatively close viewing distances.
SUMMARY
A system for providing an enhanced immersive display environment includes a number of novel features designed to enhance the performance of an immersive dome over presently-known immersive dome environments. Projectors are mounted in a multi-tier tower, out of sight beneath a viewing platform positioned to provide optimal wrap-around viewing. The projection surface consists of open-cell foam that allows passage of behind-surface sound into the dome while allowing unwanted ambient noise within the dome to escape. A visually-reflective coating, in conjunction with the open cell structure, provides a textured surface that acts as a micro-baffle and suppresses cross-reflection of projected imagery.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 depicts a side view of a system that includes an immersive dome, projector array and viewing platform;
FIG. 2 depicts a dome flattened to lower the ceiling height in the system of FIG. 1;
FIG. 3 depicts a top-view schematic of the projector array in the system of FIG. 1;
FIG. 4 depicts a top view of a single tier of the projector mounts in the projector array;
FIG. 5 depicts a side view of a single projector mount;
FIG. 6 depicts the relationship between the physical tiers of projectors and the corresponding azimuthal bands on the dome.
FIG. 7 depicts the framework of the immersive dome of FIG. 1;
FIG. 8 depicts a cross-section of the surface of the immersive dome of FIG. 1;
FIG. 9 depicts cross-reflectance suppression in an open cell foam structure; and
FIG. 10 depicts an engineered surface for suppressing cross-reflectance.



DETAILED DESCRIPTION
A system for providing an enhanced immersive display environment includes a number of novel features designed to enhance the performance of an immersive dome over presently-known immersive dome environments. Projectors are mounted in a multi-tier tower, out of sight below a viewing platform positioned to provide optimal wrap-around viewing. The projection surface consists of open-cell foam that allows passage of behind-surface sound into the dome while allowing unwanted ambient noise within the dome to escape. A visually-reflective coating, in conjunction with the open cell structure, provides a textured surface that acts as a micro-baffle and suppresses cross-reflection of projected imagery.
Tiered Projector Array Beneath Viewing Platform
Furthermore, in order to minimize distortion and brightness variations, it is desirable to place the projectors equidistant from the dome surface. Thus, the optimum location for the projectors is as close to the center of the dome as possible. It is also desirable that a mounting arrangement for the projectors should accommodate multiple projectors kept out of view of the audience while completely illuminating the available display surface.
The system includes a projector and viewing arrangement that maximizes the area for observers while minimizing the visibility of projectors, ensures that no projectors or other structures are shadowed on or otherwise obstruct the view of the dome from the viewing platform and allows maximum, unobstructed illumination of the dome surface.
FIG. 1 depicts a side view of a system that includes at least an immersive dome, projector array and viewing platform. In an embodiment, an array of projectors 10 is mounted in a tower 11; the base of the tower is at or slightly below the dome equator, and the tower axis is centered within the dome. The projectors are stacked in semi-circular or circular tiers 12, each of which projects onto an azimuthal band 13 of the dome 14. The number of projectors covering each band decreases as ascension increases and the diameter of the band narrows. The arrangement accommodates a large number of projectors for ultra-high resolution imagery. For projection at high ascension angles, e.g. the top of the dome, additional projectors 15 may be mounted on each side of the tower, outside of the viewer's desired visual field. The imagery from the multiple projectors is warped, blended, color corrected, and intensity matched to form a seamless display.
In an embodiment, a viewing platform 16 is mounted on top of the projector tower, placing viewers 17 above the equator of the dome to provide an optimum field of view. Because the projectors are below the platform floor, they are not visible and cannot be inadvertently blocked by movement of the viewers.
In an embodiment, a plurality of high-definition projectors is used to form an image on a partial dome 38 feet in diameter. In an embodiment, the high-definition projectors have a resolution of approximately 1920×1080 pixels. In an embodiment, the plurality of high-definition projectors numbers approximately 50 projectors. The partial dome spans an arc of approximately 210 degrees in azimuth and approximately 90 degrees in ascension.
In an embodiment, a fillet 18 at the equator of the dome transitions the curved dome to a strip of floor interior to the lower latitudinal terminus of the fillet to allow projection at ascensions beneath the equator. In an embodiment, the fillet has a tighter radius of curvature than the adjacent partial dome. This reduction in curvature combined with the strip of floor, results in a non-spherical region within the projection surface but reduces the amount of physical space required to extend the projection surface to ascensions further below the viewing platform, as well as lowering the required height of the platform.
In an embodiment, the displayed imagery is pre-distorted to offset the distortion that results from projecting onto the non-spherical regions, that is, the fillet and floor strip, of the projection surface. The non-spherical shape of the projection surface also demands a greater depth of field and thus, a smaller aperture in the projection optics than would be required in a perfectly spherical dome if image sharpness is to be maintained. The space savings described above must therefore be balanced against the resulting reduction in image sharpness and/or brightness. This tradeoff is mitigated, however, by the fact that the non-spherical regions of the projection surface are near the periphery of the visual field of a viewer positioned on the platform.
With regard to the projector arrangement, the dome is not limited to the shape described above, but may be within a range between purely spherical and aspherical.
For example, FIG. 2 depicts a dome flattened to lower the ceiling height. This may be done to accommodate the top of the dome 18 under a roof structure 19, where a constant radius dome 20 would not fit. The tradeoff is that further pre-distortion is required which results in reduced brightness and sharpness. Because intensity is matched among all projectors, the reduction in brightness and sharpness has the effect of lowering the brightness of the entire dome projection.
FIG. 3 depicts a top-view schematic of the projector arrangement. For clarity, one tier 30 is shown. As noted, the projectors are mounted in a tower below the viewing platform. Because the projectors are below the platform, they are not visible to viewers positioned there. However, the need to illuminate the top portion of the dome, directly over the viewing platform, dictates projectors to cover this area be mounted so as to protrude beyond the edge of the platform. Alternatively, these high-angle projectors may be placed in additional fixtures 15 apart from the projector tower, for example on either side of and behind the center of the tower, where they are not readily visible when viewing the surface of a partial dome.
FIG. 4 depicts a top view of one tier of the projector mounts, while FIG. 5 depicts a side view of a single projector mount. In an embodiment, the tier framework 40 is composed of square section steel tubing, with two welded square section steel tubes forming arms 41 on which a rigid platform 42 is mounted. The projector 43 is affixed to this platform.
FIG. 6 depicts the relationship between the physical tiers of projectors and the corresponding azimuthal bands of the dome surface onto which each tier projects. In an embodiment, 46 projectors are stacked in 6 tiers in a tower centered at the base of the dome and two sets of 2 projectors are mounted at high angles on separate fixtures on either side of the tower. Each tier 50 of projectors covers a corresponding azimuthal band 51 of the dome, and the tiers of projectors are configured to provide consistent resolution, from the smaller diameter bands at the top of the dome to the larger diameter bands at the base of the dome.
The number of projectors is based on at least several factors. Among these are:

    
    
        availability of relatively inexpensive standard high-definition (HD) projectors;
        desired size of the dome (ideally about 20 feet from the viewer, following which stereo vision is less effective); and
        sufficient illumination of the projected imagery at the dome distance.
    
    


For maximum detail, the number of pixels on the dome will ideally match or exceed the eye-limited resolution of about 1 arc-minute per line pair.
If the azimuthal bands are numbered from highest to lowest ascension and the projector tiers are numbered from the top of the projector tower to its base, the bands and tiers correspond as follows:











TABLE 1







Azimuthal Band
Number of




on Dome
Projectors
Mounting Location









1 (top of dome)
4
side-mounted in two sets





(not in tower)



2
5
Tier 3



3
7
Tier 4



4
7
Tier 5



5
9
Tier 6



6
9
Tier 2



7 (base of dome)
9
Tier 1










Therefore, the physical stacking of the tiers in the projector tower is as follows, from top to base:

Tier 1: 9 projectors (Band 7);
Tier 2: 9 projectors (Band 6);
Tier 3: 5 projectors (Band 2);
Tier 4: 7 projectors (Band 3);
Tier 5: 7 projectors (Band 4); and
Tier 6: 9 projectors (Band 5).
The viewing platform and projector tower are oriented in relation to each other such that the viewing platform is unobstructed by the projector tower and the projector tower does not obstruct the line of sight of a viewer on the viewing platform looking at any portion of the display surface. In an embodiment, the viewing platform is mounted on top of the projector tower and centered on the equatorial axis of the dome. For a viewer positioned at the forward edge of the platform, the display surface extends below the viewer's position and fills his/her peripheral vision with an azimuthal field of view of approximately 225 degrees—an increase over the 210 degree field of view at the center of the platform. It may be readily seen that, in an embodiment, a field of view of up to 360 degrees in azimuth is achieved by extending the projector tiers to complete circles.
Use of a large number of projectors enables eye-limiting resolution and high light output on a sizable dome using off-the-shelf high-definition projectors, even taking into account the percentage of overlap required for smooth blending of images. Although it is possible to abut warped images on a curved surface without overlap—commonly known as “hard seams”—this approach demands precise control of light levels and brightness, and the slightest deviation, misalignment or off-axis viewing will reveal the seams. It is more practical and robust to overlap images between projectors, with the degree of overlap ranging from a few percent to one-third or more, thus reducing the total number of pixels seen on the dome surface. Smoother blending, which may include any of matching geometry, color and intensity, is possible as the degree of overlap increases.
Warp correction may be achieved by projecting a grid or other test pattern from each projector, then using a camera to view the projected image to enable calculation of the pre-distortion required. The closer each projector is to the center of the dome, the more the lens axis is normal to the dome surface with consequently less warp required The geometry of the invention is advantageous in this regard as well, since the projectors are closely clustered about the geometric center of the dome.
Additionally, the resolution of the dome may be varied as desired. Fewer projectors can be used in each tier and/or the number of tiers reduced, trading off pixel count for wider fields of view. If more resolution is desired, projectors can be added by stacking additional tiers and/or increasing the diameter of each tier. The number of projectors may also be adjusted to suit the desired brightness or to adjust resolution to the size of the dome.
Acoustically Transparent, Micro-Baffled Projection Surface
A directionally accurate audio system is important for immersive environments, as directional cues and realistic sound effects synchronized with imagery enhance the visualization experience. The presence of a large projection surface wrapped around the viewer suggests placement of speakers behind the surface. In an embodiment, this is implemented by mounting multiple speakers behind the projection surface. Thus, the system includes an immersive dome having an acoustically-transparent projection surface to reduce unwanted acoustic reflection. At the same time, high reflectivity of the inner surface is preserved to maintain image brightness, while cross-reflectance from adjacent projected imagery is suppressed. To preserve the realism of the imagery and to cue the viewer to look at a particular region, the directionality of the audio source is preserved.
FIG. 7 depicts the framework of the immersive dome of FIG. 1, onto which the projection surface is mounted. The framework consists of closely spaced members 61, in one embodiment steel frames, for adequate support of the display surface.
FIG. 8 depicts a cross-section of the dome surface. This projection surface comprises a layer of a reflective material 70 over open cell foam 71, affixed to a framing support 72. In one embodiment, the foam is affixed to hook and loop strips of the very high bond variety, which are in turn glued to the metal dome framework using foam and fabric adhesive. This adhesive may also be used to glue seams of foam material together. In another embodiment, a metal mesh between the dome framing members gives support and adhesion over the entirety of the dome surface. The foam is of sufficient thickness and rigidity to maintain the desired curvature between framing supports. In one embodiment, the foam used is polyurethane having an approximate thickness of 1′′ and an approximate density of 1.3-1.4 lbs per square foot. In another embodiment, a dense, flame-resistant open-cell foam such as PYRELL (REILLY FOAM CORP., Conshohocken, Pa.) is used, with a density of 4 lbs. per square foot. In an embodiment, the projection surface comprises a layer of open-cell foam without a reflective layer.
The open cell foam used is at least partially acoustically transparent at low frequencies and absorptive at high frequencies. Speakers may be placed anywhere outside the dome for optimum directional sound between the dome surface and sound-absorptive materials in the surrounding structure. Sound from the behind-surface speakers is accordingly boosted or pre-emphasized at high frequencies to compensate for the resulting attenuation. By either absorbing or passing all sounds that emerge from the dome, the open cell foam prevents the undesirable reflection of sounds (from speakers or the audience) back to the audience. Additional sound-absorbing material is positioned outside of the dome to prevent low frequency sound emanating from within the dome from reflecting back into the dome from any surrounding structure.
In an embodiment, a visually reflective layer is applied to the inner surface of the open cell foam to provide a projection surface. Any of several types of coatings can be used, such as aluminum-based, glass bead, acrylic, or specialized screen paint. The paint color can range from white to neutral-density gray, optimized as desired for contrast, projector intensity, pixel density, background darkness, light levels, and human eye response. The coating also imparts a degree of rigidity, enabling the foam to better maintain its shape between the supports and also hides seams between foam blocks.
FIG. 9 depicts cross-reflectance suppression in the open cell foam structure. The reflective coating 70 is applied thinly enough so as not to fill or block the open cell foam structure 80. Specifically, the reflective paint coats the inside of the open cells. This yields a projection surface that reflects most light at near-normal incidence angles 81. Conversely, light approaching from more oblique incidence angles 82 is trapped in the open cell, thus reducing cross-reflectance. The result of the coating is thus a micro-baffled surface with an anisotropic (non-Lambertian) surface luminance with relatively high reflectivity at near-normal incidence, and relatively low (or near zero) reflectivity at more oblique incidence.
The coating may be applied in multiple layers, each layer having unique functional characteristics; for example, a reflective coating may first be applied to coat the open cell cavities, followed by an absorptive layer 83 to suppress cross-reflectance, lightly applied to the foam surface so as not to obstruct the cavities. In certain embodiments, the reverse may also be desirable.
In other embodiments, the projection surface constitutes an engineered surface having, for example, a machined or foamed texture that acts as a micro-baffle. FIG. 10 depicts an engineered surface 90 for suppressing cross-reflectance. Light at near-normal incidences 91 is reflected, whereas light at oblique angles 92 is trapped and dissipated in the vertical cavities 93, of which the vertical walls may be lined with a non-reflective or light-absorbent material.
In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.

## Claims

1. A system for providing an enhanced immersive display environment comprising:
a viewing platform, having a platform surface;
an apparatus for projecting immersive imagery on a curved display surface, said apparatus positioned entirely below the lowest floor plane of said viewing platform such that said apparatus does not obstruct any line of sight of any viewers on said platform surface to any portion of the display surface, said display surface extending azimuthally up to 360 degrees and, for every such azimuth, vertically from directly overhead to at least a horizontal plane extending from said lowest floor plane of said viewing platform, said apparatus comprising a plurality of projectors enabling said apparatus to be capable of projection on said display surface up to an eye-limiting resolution of one arc-minute per line pair, equivalent to approximately 70 million pixels over a hemisphere.

2. The system of claim 1, wherein said viewing platform is mounted on top of said apparatus for projecting.

3. The system of claim 2, wherein said viewing platform is supported by said apparatus for projecting.

4. The system of claim 1, wherein said apparatus for projecting is positioned at the central locus of said display surface.

5. The system of claim 1, wherein said apparatus for projecting comprises a multi-tiered projection array, each of said tiers projecting onto a distinct horizontal band of said display surface.

6. The system of claim 5, wherein said multi-tiered projection array comprises a tower having a plurality of projection devices mounted thereto in a tiered configuration.

7. The system of claim 1, wherein said curved display surface comprises a full or partial hemispherical dome.

8. The system of claim 7, wherein a curvature of an upper portion of said dome is flattened to reduce interior height.

9. The system of claim 7, wherein an equatorial azimuth of said dome is smoothly filleted into a horizontal floor.

10. The system of claim 1, wherein at least a portion of said apparatus for projecting is co-planar with an equatorial azimuth of said dome.

11. The system of claim 1, wherein a field of view of a viewer positioned on said viewing platform is variable by extending the azimuth of said display surface up to 360 degrees, and any of:
placing additional projection devices along each tier, such that said tier of said projection devices projects up to 360 degrees in azimuth; and
increasing the spacing between said projection devices in each tier and the projection angle of each said projector, such that said tier of said projection devices projects up to 360 degrees in azimuth.

12. The system of claim 1, wherein said display surface extends at least ten degrees below the lowest floor plane of said viewing platform.

13. A method for enhancing an immersive display environment comprising the steps of:
projecting images on a display surface of an immersive dome by means of an array of projection devices, said array of projection devices comprising a plurality of projectors, being mounted on a tower in a tiered configuration, and being capable of projection on said display surface up to an eye-limiting resolution of one arc-minute per line pair, equivalent to approximately 70 million pixels over a hemisphere; and
mounting a viewing platform, having a platform surface, on top of said tower, such that said array of projection devices lies entirely beneath the lowest floor plane of said viewing platform, such that every line of sight, to any portion of said display surface, of every viewer positioned on said platform surface is unobstructed by said array of projection devices, said display surface extending azimuthally up to 360 degrees and, for every such azimuth, vertically from directly overhead to at least a horizontal plane extending from said lowest floor plane of said viewing platform.

14. The method of claim 13, further comprising the step of:
supporting said viewing platform by said tower.

15. The method of claim 13, wherein said step of projecting images on the display surface comprises the steps of:
reducing the total number of pixels seen on the display surface by overlapping projected images between projectors, which said reducing of pixels enables smooth blending of images; and
performing warp correction by:
projecting a test pattern from each projector; and
viewing said projected image of said test pattern with a camera to calculate a value for pre-distortion required.

16. The method of claim 13, further comprising the step of:
varying resolution of said immersive dome by varying any of:
number of projectors in each tier;
number of tiers;
diameter of one or more tiers;
projection angle of said projectors; and
total number of projectors.

17. The method of claim 13, further comprising the step of varying the field of view of said immersive dome by extending the azimuth of said display surface up to 360 degrees, and any of:
placing additional projection devices along each tier, such that said tier of said projection devices projects up to 360 degrees in azimuth; and
increasing the spacing between said projection devices in each tier and the projection angle of each said projector, such that said tier of said projection devices projects up to 360 degrees in azimuth.

18. The method of claim 13, wherein said display surface extends at least ten degrees below the lowest floor plane of said viewing platform.