Abstract:
A display system for presenting one or more planes of display information. The display system may include two or more display modules positioned in a spaced relationship in a stacked formation substantially along a Z-axis perpendicular to a display face of a display module. Each display module may be selectively activated to display a visual image or deactivated to a quiescent state. Further, when a display module is activated to display the viewed image, the viewed image can be viewed through a prior display module which is deactivated to a quiescent state.

Description:
TECHNICAL FIELD  
       [0001]     The present invention primarily relates to the field of flat panel displays, particularly as implemented in systems where redundancy is desired and/or required to insure continued display performance in the face of potential device failure. The present invention also applies to multi-level security applications directly exploiting a display exhibiting different classification levels of information displayed on each screen (i.e., hardware separation of different security levels). The present invention also applies to three-dimensional (3D) imaging applications where explicit Z-axis information is viewed directly via overlay replication without recourse to stereoscopic techniques, and even to applications requiring “reality overlay” capability.  
       BACKGROUND INFORMATION  
       [0002]     In various critical applications (mission-critical, flight-critical, space-critical) where a display system must exhibit a minimal level of fault tolerance, flat panel displays and their CRT-based counterparts achieve redundancy by way of adjacent tandem dual installation. Additional area on the surface of the console that houses the display is routinely allocated for installation of backup displays and instrumentation devices. In many applications (e.g., avionics, military vehicle deployments, etc.), such “real estate” is at a premium, leading to a congested console with primary and secondary displays consuming precious console surface area.  
         [0003]     Redundancy has been traditionally achieved by allocating additional area on the X-Y surface of the console. Extension in the X-Y direction is mandated due to one factor that all such display devices have in common: they are opaque structures. Because they are inherently opaque structures, it is not possible to exploit the Z-axis in developing redundant display solutions. Thus, there is a need in the art for a display system that exploits the Z-axis in lieu of consuming more area on the X-Y console surface, many significant advantages would accrue.  
       SUMMARY OF THE INVENTION  
       [0004]     A first advantage of the present invention where the Z-axis is exploited is that redundancy achieved by exploiting the Z-axis would directly free up surface area on the display console. A second advantage is that the space savings could readily be translated into larger, easier-to-read displays. A third advantage is that system wiring paths would be shorter and thus more reliable. A fourth advantage is an ergonomic one that is particularly apparent in avionics. Since the backup display occupies the exact same location in the console, the user does not have to divert his gaze to another location on the console to acquire important information. All information is displayed in the same place under all conditions.  
         [0005]     If a flat panel display were transparent, there would be little in principle to bar its being stacked in the Z-axis in pairs, or sets of three, etc. Flat panel displays conducive to such configuration must exhibit four properties: they must be inherently transparent, they must fail in the “off mode” to avoid undesirable overlay, they must be relatively thin along the Z-axis, and they must fulfill the survivability criteria for the particular environment calling for redundant implementation. (E.g., an environment requiring redundancy is likely to undergo extremes of temperature, militating against liquid crystal display deployment at the outset. Some severe deployments may require surviving an electromagnetic pulse.)  
         [0006]     Among current display technologies, virtually none exhibit the required transparency. Accordingly, little has been done to explore the possibility of achieving redundancy using Z-axis disposition of the redundant display components. The problem has remained unsolved, although it is surely as urgent as it ever has been.  
         [0007]     The present invention, called Z-Axis Redundant Display/Multilayer Display, achieves this elusive goal for displays that satisfy these four criteria. Among the display technologies that do indeed satisfy these criteria, therefore lending themselves to implementation of a Z-Axis Redundant Display/Multilayer Display, is the display disclosed in U.S. Pat. No. 5,319,491, which is hereby incorporated herein by reference in its entirety.  
         [0008]     The display of U.S. Pat. No. 5,319,491 (hereinafter called a “TMOS Display”) is a known suitable candidate for systemic configuration into a Z-Axis Redundant Display. It exhibits the requisite transparency, it fails in the off-mode without power, and it satisfies the performance/environmental/survivability criteria associated with applications demanding fault tolerance through device redundancy.  
         [0009]     The present invention treats the TMOS Display as a modular element in a larger architectural construct. This construct, broadly conceived, involves the disposition of two or more TMOS Displays in spaced-apart relation to each other, said relation keeping the planes of all constituent TMOS Displays parallel. When TMOS Displays are used as the target module being replicated (as recommended), the interstitial spacing between them is nominally greater than the wavelength of the lowest frequency light traveling in each TMOS Display waveguide to avoid crosstalk between displays occasioned by evanescent coupling. The interstitial gap cannot be filled with material bearing a high refractive index, since TMOS Displays use the principle of Frustrated Total Internal Reflection to generate images. The gap may be filled with air or material with a refractive index very near that exhibited by air (1.00-1.06). The present invention can incorporate displays other than TMOS Displays that fulfill the criteria enunciated above; the limitations inherent in these alternate candidates would directly influence the geometry of the construct. From this point forward, the term “module” will be taken to mean a TMOS Display or a generally equivalent alternate candidate that satisfies the key viability criteria herein tabulated. The term “construct” will refer to the systemic composition of two or more modules in spaced-apart relation to secure the benefits accruing to such composition.  
         [0010]     The primary display in a construct may be the topmost/frontmost module, with the backup display(s) being one or more modules situated underneath/behind it. In one embodiment, only the primary display operates while the backup display(s) remain(s) quiescent. In the event of failure of the primary display, the appropriate circuitry either detects this fact or is apprised of it by operator action, shuts down power to the primary display, activates the next backup display and reroutes video signals to the latter. If more than simple redundancy obtains, the failure of the secondary display would trigger the activation of a tertiary display, etc., thus securing additional redundancy as required.  
         [0011]     The present invention is independent of any specific mounting technology to hold the modules in the correct spaced relationship in the construct. It broadly covers all implementations of display redundancy in which the salient features herein disclosed are in evidence. There may well be levels of sophistication in such mounting technologies that enable ease of module replacement within the construct. There may also be many variations in how to reroute information from the failed primary display to a backup display (from one module to another). The present invention discloses an overarching architecture from which such present and future sophistications derive meaning and utility.  
         [0012]     To achieve so-called “hardware separation” between data bearing different security/classification levels, the same parallel module disposition can be applied. In this instance, the driver circuitry is not geared to redundancy but rather to keeping displayed data bearing a specific security clearance level on a specific module within the module “stack.” Users of such systems who lack the appropriate security clearances will not receive information restricted to the corresponding module since that module will be deactivated or otherwise rendered quiescent. Only the modules in the stack for which the user has clearance will be activated and permitted to display information.  
         [0013]     Where a sufficiently large number of modules comprise a stack, it is feasible to emulate explicit 3-dimensional objects by encoding the 2-dimensional projected cross-section of these objects into the respective planes represented by the modules. The level of Z-axis granularity under this emulation schema will be proportional to the number of modules comprising the stack and inversely proportional to inter-module spacing.  
         [0014]     Applying redundancy to “reality overlay” applications (e.g., helmet-mounted see-through displays) is also readily achieved by applying the principles of the disclosed construct to the device under contemplation. Since both modules are transparent, the reality overlay criterion (the ability to view the real world through the display, which is usually situated near the observer&#39;s eye) is maintained under standard operating mode with the primary display or in emergency backup mode with the secondary display within the construct displaying the viewable image.  
         [0015]     In the case of a reality overlay display application, there is no opaque layer comprising the final part of the construct, inasmuch as such a layer would be inconsistent with the “see through” criterion at the heart of such a system. However, such an opaque (black) layer may be used to provide a reference black background against which images are generated. There are two different ways to implement such an opaque background within the construct: (1) if the opaque background is static (fixed and unchanging in blackness), such as would be the case if it were an extended planar sheet of carbon nanofoam, the layer must be placed behind all the other modules; (2) if the opaque background is dynamic (capable of being switched between transparent and opaque modes), this layer can be either situated as in (1) above, or can itself be replicated behind each module so that each layer of the construct has its own dynamic black background.  
         [0016]     The foregoing has outlined rather broadly the features and technical advantages of one or more embodiments of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     A better understanding of the present invention can be obtained when the following detailed description is considered in conjunction with the following drawings, in which:  
         [0018]      FIG. 1  illustrates a single level of redundancy using a two-module construct in accordance with an embodiment of the present invention;  
         [0019]      FIG. 2  illustrates a double level of redundancy using a three-module construct in accordance with an embodiment of the present invention;  
         [0020]      FIG. 3  illustrates an arbitrary level of redundancy using an n-module construct in accordance with an embodiment of the present invention;  
         [0021]      FIG. 4  illustrates a dual-module construct with a single static opaque layer at the distal end of the module stack in accordance with an embodiment of the present invention;  
         [0022]      FIG. 5  illustrates a dual-module construct with a dynamic opaque layer situated behind each individual module in the stack in accordance with an embodiment of the present invention;  
         [0023]      FIG. 6  is a flowchart of a method for achieving redundancy for a construct comprising two modules in the stack with a static opaque element in accordance with an embodiment of the present invention;  
         [0024]      FIG. 7  is a flowchart of a method for achieving redundancy for a construct comprising two modules in the stack with dynamic opaque elements situated behind each module in accordance with an embodiment of the present invention;  
         [0025]      FIG. 8  illustrates a “hardware-separated” multi-level security block diagram in accordance with an embodiment of the present invention;  
         [0026]      FIG. 9  illustrates an explicit Z-axis quasi-three-dimensional construct of arbitrary granularity in accordance with an embodiment of the present invention;  
         [0027]      FIG. 10  illustrates a “reality overlay” system exhibiting redundancy in harmony with the constructs disclosed in  FIGS. 1, 2 , and  3 , in accordance with an embodiment of the present invention;  
         [0028]      FIG. 11  is a flowchart of a method for implementing hardware separation of data at different security classifications based on the representative constructive of  FIG. 8  in accordance with an embodiment of the present invention;  
         [0029]      FIG. 12  is a flowchart of a method for quasi-three-dimensional image generation based on the construct of  FIG. 9  in accordance with an embodiment of the present invention;  
         [0030]      FIG. 13  illustrates a perspective view of a flat panel display in accordance with an embodiment of the present invention;  
         [0031]      FIG. 14A  illustrates a side view of a pixel in a deactivated state in accordance with an embodiment of the present invention;  
         [0032]      FIG. 14B  illustrates a side view of a pixel in an activated state in accordance with an embodiment of the present invention; and  
         [0033]      FIG. 15  is a flowchart of a method for displaying different classes of information on different modules in accordance with an embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0034]     In the following description, numerous specific details are set forth to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without such specific details. In other instances, well-known circuits and algorithms have been shown in block diagram form in order not to obscure the present invention in unnecessary detail. For the most part, details involving timing considerations and the like have been omitted inasmuch as such details are not necessary to obtain a complete understanding of the present invention and are within the skills of persons of ordinary skill in the relevant art.  
         [0035]     As stated in the Background Information section, a complement of transparent displays disposed in a spaced-apart relation along the Z-axis (display stacking) can provide valuable system redundancy characteristics in conjunction with improved human factors engineering (identical position for the primary and backup display for any given piece of instrumentation). As before, a transparent display, whether based on a TMOS display or an equivalent alternate technology bearing the requisite attributes, shall be termed a module, while the composition of modules into a system shall be termed a construct. A general principle of the present invention in one embodiment is illustrated in  FIG. 1 . The construct may be composed of a primary module  100  and a secondary backup module  101 , the primary planar surfaces of which are maintained in a substantially parallel spaced apart relation  102  by any arbitrarily chosen mounting mechanism (not shown). (Note, the present invention is not to be limited to such parallel constructions; it is also applicable to modules positioned at angles to each other.) The invention relates to the achievement of useful display redundancy, and therefore generalizes the means for mounting the displays in the correct geometric relations. Such mounting mechanisms can incorporate shock and vibration absorbing mechanisms, signal interconnects, etc. The invention can coexist with any such sophistications in mounting the modules; in fact, it directs the purpose for the mounting mechanisms to be ultimately chosen for any given implementation of the present invention. The distance  102  may be selected to provide desired viewability of the construct in both normal and backup display operating modes (i.e., when  100  is displaying the desired image, and when  100  has failed or has been disabled and  101  is displaying the desired image, which is viewed through the now-quiescent module  100 ). The distance  102  may be zero or greater in dimension.  
         [0036]     Each module  100 ,  101  may include a matrix of optical shutters commonly referred to as pixels or picture elements as illustrated in  FIG. 13 .  FIG. 13  illustrates a module  100 ,  101  comprised of a light guidance substrate  1301  which may further comprise a flat panel matrix of pixels  1302 . Behind the light guidance substrate  1301  and in a parallel relationship with substrate  1301  may be a transparent (e.g., glass, plastic, etc.) substrate  1303 . It is noted that module  100 ,  101  may comprise other elements than those illustrated, such as disclosed in U.S. Pat. No. 5,319,491, which is hereby incorporated herein by reference in its entirety. It is further noted that each module discussed herein may be structured as disclosed in  FIG. 13 .  
         [0037]     Each pixel  1302 , as illustrated in  FIGS. 14A and 14B , may comprise a glass substrate  1303 , light guidance substrate  1401 , a transparent conductive ground plane  1402 , a deformable elastomer layer  1403 , and a transparent electrode  1404 .  
         [0038]     Pixel  1302  may further comprise a transparent element shown for convenience of description as disk  1405  (but not limited to a disk shape), disposed on the top surface of electrode  1404 , and formed of high-refractive index material, preferably the same material as comprises light guidance substrate  1401 .  
         [0039]     In this particular embodiment, it is necessary that the distance between light guidance substrate  1401  and disk  1405  be controlled very accurately. In particular, it has been found that in the quiescent state, the distance between light guidance substrate  1401  and disk  1405  should be approximately 1.5 times the wavelength of the guided light, but in any event this distance must be maintained greater than one wavelength. Thus the relative thicknesses of ground plane  1402 , deformable elastomer layer  1403 , and electrode  1404  are adjusted accordingly. In the active state, disk  1405  must be pulled by capacitative action, as discussed below, to a distance of less than one wavelength from the top surface of light guidance substrate  1401 .  
         [0040]     In operation, pixel  1302  exploits an evanescent coupling effect, whereby TIR (Total Internal Reflection) is violated at pixel  1302  by modifying the geometry of deformable elastomer layer  1403  such that, under the capacitative attraction effect, a concavity  1406  results (which can be seen in  FIG. 14B ). This resulting concavity  1406  brings disk  1405  within the limit of the light guidance substrate&#39;s evanescent field (generally extending outward from the light guidance substrate  1401  up to one wavelength in distance). The electromagnetic wave nature of light causes the light to “jump” the intervening low-refractive-index cladding, i.e., deformable elastomer layer  1403 , across to the coupling disk  1405  attached to the electrostatically-actuated dynamic concavity  1406 , thus defeating the guidance condition and TIR. Light ray  1407  (shown in  FIG. 14A ) indicates the quiescent, light guiding state. Light ray  208  (shown in  FIG. 14B ) indicates the active state wherein light is coupled out of light guidance substrate  1401 .  
         [0041]     The distance between electrode  1404  and ground plane  1402  may be extremely small, e.g., 1 micrometer, and occupied by deformable layer  1403  such as a thin deposition of room temperature vulcanizing silicone. While the voltage is small, the electric field between the parallel plates of the capacitor (in effect, electrode  1404  and ground plane  1402  form a parallel plate capacitor) is high enough to impose a deforming force thereby deforming elastomer layer  1403  as illustrated in  FIG. 14B . Light that is guided within guided substrate  1401  will strike the deformation at an angle of incidence greater than the critical angle for the refractive indices present and will couple light out of the substrate  1401  through electrode  1404  and disk  1405 .  
         [0042]     The electric field between the parallel plates of the capacitor may be controlled by the charging and discharging of the capacitor which effectively causes the attraction between electrode  1404  and ground plane  1402 . By charging the capacitor, the strength of the electrostatic forces between the plates increases thereby deforming elastomer layer  1403  to couple light out of the substrate  1401  through electrode  1404  and disk  1405  as illustrated in  FIG. 14B . By discharging the capacitor, elastomer layer  1403  returns to its original geometric shape thereby ceasing the coupling of light out of light guidance substrate  1401  as illustrated in  FIG. 14A . Additional details regarding the functionality of pixels  1302  is disclosed in U.S. Pat. No. 5,319,491, which is hereby incorporated herein by reference in its entirety.  
         [0043]     Returning to  FIG. 1 , whereas  FIG. 1  illustrates a construct exhibiting simple redundancy (a single backup module),  FIG. 2  illustrates an embodiment of the present invention of a construct with double redundancy (employing both a secondary and a tertiary module for backing up the primary module). The primary module  200  is in parallel spaced apart relation to the first backup module  201 , which is in turn in parallel spaced apart relation to the second backup module  202 . The distances between primary and secondary modules ( 203 ) and between secondary and tertiary modules ( 204 ) satisfy the criteria previously disclosed for  FIG. 1 , passim.  
         [0044]      FIG. 3  generalizes the present invention to any arbitrary level of system redundancy and fault tolerance in accordance with an embodiment of the present invention. The primary display  300  has additional displays in spaced apart relation  302  to it in a concatenated stacking sequence, up through the final level of redundancy represented by the last module in the stack,  301 . The spacing  301  between each element of this construct satisfies the criteria established for such interstitial spacing in  FIG. 1 . Any module in the stack may be used as the primary display. Moreover, more than one module may be active at the same time.  
         [0045]      FIG. 4  illustrates the construct of  FIG. 1  with the addition of a static opaque (black) planar background in accordance with an embodiment of the present invention. Module  400  is in parallel spaced-apart relation  403  to backup module  401 , while the static opaque planar background  402  is itself in spaced-apart relation  404  to backup module  402 . The planar background  402  is termed static because it is considered permanently opaque, and not capable of dynamic shifting between opaque and transparent states. It provides a contrasting background for the construct as a whole, both for  400  when it is operational as well as for  401  when it is activated and displaying the image encoded in the video signal being fed to the construct.  
         [0046]      FIG. 5  illustrates the construct of  FIG. 1  with the addition of at least one dynamic opaque (black) planar background in accordance with an embodiment of the present invention. The primary module  500  is in parallel spaced apart relation to the backup module  502 , whereas both  500  and  502  have associated opaque planar backgrounds ( 501  and  503  respectively) in parallel spaced-apart relation to them, such that  501  is situated between  500  and  502 , while  503  is situated on the obverse side of  502  from  501 . Opaque planar background  501  must be capable of dynamically shifting from opaque to transparent mode, while  502  may be either a static or dynamic opaque planar background. When  500  is operational,  501  may be in opaque (black) mode. Should  500  fail or be deactivated, element  501  then becomes transparent in order for backup module  502  to be viewed through the combination of  500  and  501 , with  503  being set to opaque if it is dynamic rather than static in nature.  
         [0047]      FIG. 6  illustrates an embodiment of the present invention of an algorithm of a simple redundancy construct, such as in  FIG. 1 . The algorithm applies to instances where a static planar background, as in  FIG. 4 , is incorporated. Referring to  FIG. 6 , the algorithm  600  of a simple redundancy construct may determine if the primary display failure has been detected in step  601 . If the failure has not been detected, then a determination is made in step  602  as to whether the operator initiated a reversion to the backup display. If the operator has not initiated a reversion to the backup display then, in step  603 , a system clock initiates periodic polling of the primary display failure detection and operator commands. Subsequent to the system clock initiating periodic polling of the primary display failure detection and operator commands, a determination is made in step  601  as to whether the primary display failure has been detected.  
         [0048]     If the primary display failure has been detected, then, in step  604 , the primary display is deactivated to place the primary display in a quiescent, fully transparent state. Referring to step  603 , if the operator initiated a reversion to the backup display, then, step  604 , the primary display is deactivated to place the primary display in a quiescent, fully transparent state.  
         [0049]     In step  605 , the secondary display is activated and the video signals are routed to the secondary display instead of to the primary display.  
         [0050]     Where dynamic planar backgrounds are implemented, the modified algorithm of  FIG. 7  may be imposed. It should be understood that both algorithms ( FIGS. 6 and 7 ) are readily extensible and thus can be modified by anyone knowledgeable in the art to handle higher degrees of system redundancy for more elaborate constructs, such as those disclosed in  FIG. 2  or  FIG. 3 .  
         [0051]     Referring to  FIG. 7 ,  FIG. 7  illustrates an embodiment of the present invention of an algorithm  700  where dynamic planar backgrounds are implemented. In step  701 , a determination is made as to whether the primary display failure has been detected. If the failure has not been detected, then a determination is made in step  702  as to whether the operator initiated a reversion to the backup display. If the operator has not initiated a reversion to the backup display then, in step  703 , a system clock initiates periodic polling of the primary display failure detection and operator commands. Subsequent to the system clock initiating periodic polling of the primary display failure detection and operator commands, a determination is made in step  701  as to whether the primary display failure has been detected.  
         [0052]     If the primary display failure has been detected, then, in step  704 , the primary display is deactivated to place the primary display in a quiescent, fully transparent state. Referring to step  703 , if the operator initiated a reversion to the backup display, then, step  704 , the primary display is deactivated to place the primary display in a quiescent, fully transparent state.  
         [0053]     In step  705 , the primary display&#39;s dynamic opaque back layer is deactivated thereby making the primary display&#39;s dynamic opaque back layer transparent. Further, in step  705 , the secondary display&#39;s dynamic back layer is activated thereby making the secondary display&#39;s dynamic back layer opaque.  
         [0054]     In step  706 , secondary display is activated and the video signals are routed to the secondary display instead of to the primary display.  
         [0055]      FIG. 8  illustrates application of an embodiment of the present invention to the situation where hardware separation of displayed information is required to achieve multi-level security. For illustrative purposes, one can assume that module  800  is hardwired to display information deemed “unclassified,” while module  801  is hardwired to display information deemed “confidential” while module  802  is hardwired to display information deemed “secret.” The information system of which this triplexed construct is a part would determine by user password analysis which of the displays will be activated and which ones will not, thus providing valuable hardware separation of security levels in the display of sensitive information. The parallel spaced-apart relationships  803  and  804  follow the general criteria for such interstitial distances disclosed earlier. A method for displaying different classes of information on different modules is discussed below.  
         [0056]      FIG. 15  is a flowchart of an embodiment of the present invention of a method  1500  for displaying different classes of information on different modules in accordance with an embodiment of the present invention.  
         [0057]     Referring to  FIG. 15 , in step  1501 , a first module, e.g., module  800  ( FIG. 8 ), is hardwired to display unclassified information. In one embodiment, the first module may be hardwired to display unclassified information only if the user enters a password designated to allow the user to retrieve unclassified information.  
         [0058]     In step  1502 , a second module, e.g., module  801  ( FIG. 8 ), is hardwired to display classified information. In one embodiment, the second module may be hardwired to display classified information only if the user enters a password designated to allow the user to retrieve classified information. The password that allows the user to retrieve classified information may be different from the password that allows the user to retrieve unclassified information.  
         [0059]     In step  1503 , a third module, e.g., module  802  ( FIG. 8 ), is hardwired to display secret information. In one embodiment, the third module may be hardwired to display secret information only if the user enters a password designated to allow the user to retrieve secret information. This password may be different from the passwords that allow the user to retrieve unclassified and classified information.  
         [0060]     Referring to  FIG. 9 ,  FIG. 9  illustrates the possibility of using an arbitrarily complex construct composed of many modules ( 900 ,  901 , and all modules between them represented in dotted-outline format) in accordance with an embodiment of the present invention. Each of the modules is in parallel spaced-apart relation  902  with its neighboring counterparts in the stack. The quality of the three-dimensional imagines generated is proportional to the number of modules and inversely proportional to the distance  902 , which defines the construct&#39;s Z-axis granularity. With properly encoded information, it is possible to generate a quasi-three-dimensional image using this construct. The example suggested by  FIG. 9  is of a solid cylinder with its central axis being perpendicular to the planar surfaces of the modules  900  through  901  comprising the construct. Each module in the stack comprising the construct displays the line of intersection between the three dimensional object being displayed and the plane of the module. For this reason, the modules between  900  and  901  are shown as displaying only the outer ring of the cylinder. Excessive directionality of optical output power would vitiate the desired effect of solid objects being displayed within the limits of the construct.  
         [0061]      FIG. 10  illustrates a “reality overlay” display system that incorporates simple (single level) redundancy in accordance with an embodiment of the present invention. During normal operation, the observer views the world through both modules  1000  and  1001 . Module  1000  is the primary display, which may or may not be displaying information to be overlaid on the real-world image as seen through the module. Such displayed information as would appear on  1000  can be advisory, or it can include targeting reticles, digitally enhanced images, etc. Should module  1000  fail or be disengaged by the observer, module  1001 , which is in parallel spaced apart relation  1002  to module  1000 , will be activated, and the observer will again view the real world through both  1000  and  1001 , but the overlaid information will be emitted from the surface of  1001  rather than  1000 . By definition, reality overlay display applications do not incorporate any opaque components, such as might be found in other display applications herein.  
         [0062]      FIG. 11  is an embodiment of the present invention of a flowchart of a method  1100  for implementing multi-level security using hardware separation as explicated in the description of  FIG. 8 . The various terms (login, polling, etc.) are not to be construed in a restrictive sense, but broadly, in keeping with the general principles well-known to anyone skilled in the art of systems security.  
         [0063]     Referring to  FIG. 11 , in step  1101 , a determination is made as to whether the login flag is set for the first security level. If the login flag is not set for the first security level, then in step  1102 , a determination is made as to whether the login flag is set for the second security level. If the login flag is not set for the second security level, then in step  1103 , a determination is made as to whether the login flag is set for the third security level. If the login flag is not set for the third security level, then in step  1104 , all secure displays are deactivated and reverted to login mode. In step  1105 , the user logins to the system to set security flags that determine which displays are active. Upon setting security flags that determine which displays are active, a determination is made as to whether the login flag is set for the first security level in step  1101 .  
         [0064]     If the login flag is set for the first security level, then in step  1106 , display  800  ( FIG. 8 ), associated with a first level of security clearance, is activated. In step  1109 , the user logs out of the system or other semaphore is activated that flags for deactivation. Upon logging out of the system or activating a flag for deactivation, all secure displays are deactivated and reverted to login mode in step  1104 .  
         [0065]     If the login flag is set for the second security level, then in step  1107 , display  801  ( FIG. 8 ), associated with a second level of security clearance, is activated. In step  1109 , the user logs out of the system or other semaphore is activated that flags for deactivation. Upon logging out of the system or activating a flag for deactivation, all secure displays are deactivated and reverted to login mode in step  1104 .  
         [0066]     If the login flag is set for the third security level, then in step  1108 , display  802  ( FIG. 8 ), associated with a third level of security clearance, is activated. In step  1109 , the user logs out of the system or other semaphore is activated that flags for deactivation. Upon logging out of the system or activating a flag for deactivation, all secure displays are deactivated and reverted to login mode in step  1104 .  
         [0067]      FIG. 12  is an embodiment of the present invention of a method  1200  for implementing quasi-three-dimensional imaging using the multiplicity of overlaid displays suggested in  FIG. 9 . In order to keep projected energies proportional to the surface contours of the objects being displayed within this system, only the surface of the object is generated. The intersection of this surface with the virtual plane formed by each of the elements between display  900  and  901  inclusive (viz, including  900  and  901  themselves) provides the encoding framework for feeding the appropriate information to each element with the construct contemplated in  FIG. 9 .  
         [0068]     Referring to  FIG. 12 , in step  1201 , the insertion of the 3-D object&#39;s surface with the virtual plane of the display is determined for each display within the multiplicity disposed between  900  ( FIG. 9 ) and  901  ( FIG. 9 ). In step  1202 , a determination is made as to whether the calculated intersection does exist and can be encoded.  
         [0069]     If the calculated intersection does exist and can be encoded, then, in step  1203 , the line of intersection between the 3-D solid object and the virtual plane of the selected display is encoded and that image is generated on the display. In step  1204 , a determination is made as to whether all the displays between  900  and  901  have been polled.  
         [0070]     If, however, the calculated intersection does not exist and/or cannot be encoded, then in step  1204 , a determination is made as to whether all the displays between  900  and  901  have been polled.  
         [0071]     If all the displays between  900  and  901  have not been polled, then in step  1201 , the insertion of the 3-D object&#39;s surface with the virtual plane of the display is determined for each display within the multiplicity disposed between  900  and  901 .  
         [0072]     If, however, all the displays between  900  and  901  have been polled, then in step  1205 , a frame of image data containing the data describing the 3-D objects is accepted. Upon accepting the frame of image data, the insertion of the 3-D object&#39;s surface with the virtual plane of the display is determined for each display within the multiplicity disposed between  900  and  901  in step  1201 .  
         [0073]     Although the system and method are described in connection with several embodiments, it is not intended to be limited to the specific forms set forth herein, but on the contrary, it is intended to cover such alternatives, modifications and equivalents, as can be reasonably included within the spirit and scope of the invention as defined by the appended claims.