Compact simulator system theater

A compact theater for use with a simulator system includes a motion base moveable only along three mutually orthogonal displacement axes by means of displaceable actuators. A projector and screen are included for providing a sequence of audio signals and visual images to the occupants. A motion base controller generates actuator drive signals. A system controller provides the command signals to the motion base controller in synchronization with the presentation of the audio-visual images. The system controller generates the motion base command signals such that the displacement of the motion base is synchronized to the presentation of the audio signals and visual images. The motion base is characterized by a reduced height when fully retracted such that, when configured with the projector and screen, the total height is less than conventional simulators, enabling the present theater to be housed within buildings of a standard commercial height.

TECHNICAL FIELD 
The present invention relates to simulators generally and in particular to 
a theater housing a simulator system that is characterized by compact 
dimensions. 
1. Cross Reference to Related Application 
Some of the matter contained herein is disclosed and claimed in U.S. Pat. 
No. 5,199,875, entitled "A Method and Apparatus for Generating 
Supplemental Motion in a Simulator" and U.S. Pat. application Ser. No. 
08/014,117, entitled "A Simulator System Having An Orthogonal Motion Base" 
both incorporated herein by reference. 
2. Background of the Invention 
Simulators are well known in the art having found applications in such 
diverse fields as aircraft pilot training and amusement rides. In general, 
known simulators include a motion base having one or more seats and a 
plurality of programmable actuators which displace the motion base from a 
rest position in accordance with a predetermined sequence of drive 
signals. Synchronized with the motion base movement is a motion picture 
illuminated on a projection screen directly attached to the motion base or 
in the immediate environment. A controller is sometimes included to 
provide for the synchronization between the motion base displacements and 
the accompanying audio-visual work. Alternatively, the audio-visual images 
and motion base control signals are simultaneously recorded in media if, 
for example, the resultant program is to be repeatedly used. 
Known simulators include the amusement ride apparatus disclosed in U.S. 
Pat. Nos. 4,752,065 and 4,798,376, which includes a motion base that moves 
and tilts passengers viewing a motion picture. A plurality of passenger 
holding frames is provided which are all synchronously moved by separate 
sets of actuators. A film is shown to passengers on a stationary screen. 
The passenger holding frames are each pivoted up and down on a beam which 
is supported only by two largely vertical actuators while two pairs of 
links or arms limit the movement of the beam. 
U.S. Pat. No. 3,923,300 and 3,865,430, to Tanus disclose a theater chair 
that comprises a support structure and a chassis having a back, arms and a 
seat moveably affixed to the chassis. There is a provision for movement in 
the vertical and horizontal directions. The Tanus chair comprises part of 
a overall system wherein control signal information is coded on motion 
picture film. The chair is operated synchronously with the playing of the 
motion picture to enhance the realism of the movie. 
An example of a game machine is provided by U.S. Pat. No. 4,478,407, to 
Manabe. The '407 machine includes a motion base wherein a seat is 
pivotally mounted at perpendicular hinge points on a planar platform with 
motion in a perpendicular third dimension being accomplished by actuators 
configured therewith. The '407 device is designed to generate roll pitch 
and yaw sensations, as well as vertical movement. 
A motion system for flight simulation is disclosed in U.S. Pat. 3,645,011, 
to Callanen. The '011 flight simulation system includes three spaced-apart 
hydraulic actuators for imparting translation to respectively associated 
reciprocal pistons. One of the actuators is positioned in a vertical plane 
containing the longitudinal or roll axis of a grounded flight trainer and 
the other two actuators are spaced from the roll axis at vertical 
positions on either side transverse to that axis. 
Another amusement ride is disclosed in U.S. Pat. No. 4,066,256. The '256 
amusement ride creates the illusion that the passengers are seated in a 
rapidly maneuvering vehicle by applying forces to the passengers in 
synchronism with the display of a motion picture image. The '256 apparatus 
includes a passenger holding frame that has three locations resting on 
hydraulic rams that can tilt the frame or move it up and down with a film 
projector and viewing screen connected to the frame to move with it. 
U.S. Pat. No. 4,846,686, discloses a motor vehicle simulator with multiple 
images. The '686 simulator is characterized by a conventional front 
looking "driver point of view" image which would be seen by a driver 
looking through a windshield. Another section of the images displayed with 
the '686 simulator includes images that were recorded by one or more 
cameras which were facing rearward. An individual in the simulator is 
simultaneously presented with a forward looking "driver point of view" 
image and with other images representing what would be seen by the driver 
looking towards the rear of the simulator vehicle. 
U.S. Pat. No. 4,276,030, discloses a pivotable vehicle simulator with one 
end of an upper frame carrying an occupant station of a simulated vehicle. 
The upper frame is mounted to a base frame which is pivotal about a 
vertical axis. A dummy steering wheel is provided at the occupant's 
station and is linked to pivot the upper frame. Combined rotary and 
translation bearings support the other end of the upper frame on a shaft 
carried on a base frame to accommodate the pivotal movement about the 
vertical axis and also to provide a small upward pitching of the upper 
frame during pivoting of the upper frame in either direction from a 
central position so that gravity acts to restore the upper frame and 
steering wheel to centered conditions. 
Other known simulator systems rely primarily on rotational motion including 
the amusement apparatus of U.S. Pat. No. 5,060,932. the video simulation 
apparatus of U.S Pat. No. 4,856,771, and the simulation device of U.S. 
Pat. No. 4,710,129. All of the above are geared towards simulating 
simultaneous roll, yaw and pitch or combinations thereof. Some of the 
above are also configured to be used with projected images for viewing by 
occupants as part of the simulation. The amusement ride of U.S. Pat. No. 
4,066,256, is characterized by three substantially vertical hinged 
actuators which are moved in a controlled manner to displace a suspended 
horizontal platform, thereby simulating acceleration in the plane of the 
platform. 
With known simulators the movement imparted by the motion base has been 
correlated with the presentation of visual images without regard to the 
physiological effect on passengers of that combination of image and 
motion. An unanticipated and unwanted consequence has been the frequent 
inducement of motion sickness. It has been recognized that motion sickness 
stems primarily from an improper relationship between visual images and 
the corresponding motion of a person's reference frame. 
Simulators deceive the mind through the use of a combination of visual 
images coupled with limited motion of the passengers. To be effective, 
simulators must rely on tricking the inner ear with initial movement of 
the motion base synchronized with the "onset queues" presented as part of 
the visual image. The inner ear is sensitive to acceleration, i.e., the 
rate of change of velocity per unit time. The magnitude of acceleration is 
greatest at the onset of motion or at the onset of a change in motion. 
Consequently, it is most important for there to be strict correlation 
between the onset of the movement of the motion base and the corresponding 
visual image. 
Angular motion of the frame of reference has been specifically demonstrated 
to be of great importance in causing motion sickness. For example, the 
driver of a car is least susceptible to motion sickness as compared to its 
passengers. Driver visual input is almost exclusively the view down the 
road towards the horizon. As such, the driver's frame of reference 
undergoes only orthogonal, rectilinear movement. In contrast, the 
passenger's frame of reference includes the other passengers as well as 
the vehicle's interior. The heaving and bobbing of that frame while 
driving is characterized by angular motion (e.g., roll, pitch and yaw). 
Simulators, therefore, should correlate the physical and visual onset 
queues and avoid angular movement of that which comprises the passengers 
frame of reference, such as the vehicle interior. However, in the prior 
art there has been no recognition of the need to maintain orthogonal 
fidelity between motion and the visual images associated therewith or 
correlate onset queues. No prior art motion base is configured to 
constrain motion only in three orthogonal directions. In contrast, the 
prior art is unanimous in extolling the virtues of maximizing the degrees 
of freedom of the motion base and provide for rotational or angular motion 
of the vehicle, (roll, pitch and yaw) as they are directed at or derived 
from flight simulation and are constructed without regard to the 
relationship between onset queues. 
Known motion bases must be adapted to emulate orthogonal motion, requiring 
additional complexity in the controller. The hardware needed to simulate 
rotational motion is superfluous if only three orthogonal degrees of 
freedom are mandated. The cost of these prior art motion bases are 
correspondingly excessive when movement is so limited. 
Moreover, existing motion bases are large and tall, resulting in simulator 
systems that will not fit in buildings of a standard design. Commercial 
buildings typically have a maximum height of about 14.5 ft. Known 
simulator systems must, therefore, be housed in specially fabricated 
buildings. For amusement applications, new buildings must be constructed 
or existing buildings must be heavily modified, adding still more costs to 
the simulator system. 
It would be desirable to have a simulator system which generates a more 
realistic simulation of an event in a simple and cost effective manner, 
capable of installation in standard buildings while avoiding movement that 
has the potential for inducing motion sickness. The present invention is 
drawn towards such a simulator system. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a simulator system theater 
capable of enclosure within buildings of standard design. 
Another object of the present invention is to provide a theater of the 
forgoing type that includes a motion base limited to three axes of 
movement. 
Another object of the present invention is to provide a theater of the 
forgoing type that includes a motion base having a reduced height. 
Still another aspect of the present invention is to provide a theater of 
the foregoing type whose passengers are each provided displacements of 
equal magnitude by the motion base. 
According to the present invention, a simulator system theater for use in 
providing an event simulation to a plurality of occupants in a room of 
standard commercial height includes a motion base having a first member 
fixed to provide a foundation to the room floor; a second member adapted 
to be received by the first member to be moveable relative thereto only 
along a first axis; a third member adapted to be received by the second 
member to be moveable relative to the second member only along a second 
axis orthogonal to the first axis; a fourth member adapted to be received 
by the third member to be moveable relative to the third member only along 
a third, vertical axis orthogonal to both the first and second axes 
between a retracted height and an extended height as measured from the 
floor; a platform adapted to be received by the fourth member and having 
seats for the occupants. There is also a linear displacement apparatus 
including pairs of cooperatively engaging first and second linear guide 
elements affixed to adjacent ones of the members for constraining the 
members to linear movement relative to one another. A plurality of 
actuators is provided for effecting linear displacement of the members 
relative to one another in response to received actuator drive signals. An 
audio signal generator provides a sequence of audio signals to the theater 
occupants while a projector, including projection optics, presents visual 
images within a solid angle sector bounded by upper and lower planes. The 
projector is vertically separated from the motion base platform such that 
the motion base platform and the occupants in the seats do not 
substantially intersect the solid angle sector lower plane when the motion 
base is positioned at the extended height. Further, the sum of the motion 
base extended height and the projector separation is less than or equal to 
the commercial standard height of the room. A screen receives the 
projected visual images and reflects the same to the occupants. The screen 
includes a segment of a substantially spherical surface and has dimensions 
sufficient to intercept the solid angle sector upper and lower planes, 
thereby intercepting substantially all of the visual images. There is a 
motion base controller for generating the actuator drive signals in 
response to received command signals and a system controller for providing 
the command signals to the motion base controller in synchronization with 
the presentation of the audio signals and visual images.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIG. 1 there is shown a block diagram illustrating a 
simulator system 8 included in a compact theater 10 provided according to 
the present invention. The theater 10 comprises a motion base 12 which 
includes a plurality of actuators 14. The actuators are of a known 
hydraulic type and receive drive signals on lines 16 from a motion base 
controller 18. 
The theater includes a system controller 20 that provides control signals 
to projector 22 and speaker 24 as well as a viewing screen, not shown in 
the Figure. Audio signals and visual images are preferably encoded in a 
single film medium in a known manner. Command signals are provided on 
lines 26 from a storage medium such as a digital hard disc 28 to the 
motion base controller. The actuator drive signals are programmed and are 
configured to be synchronously applied to the motion base in accordance 
with the pre-programmed audio signals and visual images. As noted above, 
the motion base is preferably comprised of a plurality of hydraulic 
actuators, each of which is respectively configured with a servo valve 
(not shown) for receiving drive signals to displace the actuators a 
selected amount at a selected rate. 
FIG. 2 is a simplified schematic illustration of a preferred embodiment of 
a portion of the theater 10, including the orthogonal motion base 12. On 
screen 30 is projected an image 32 projected in any conventional 
or,rolling loop format. The screen is curved, with the preferred geometry 
being hemispherical. Passengers 34 are placed in seats 36 on a platform 
38. The preferred system seats between 12 and 15 individuals. As shown in 
a side illustration of the motion base in FIG. 3, the platform is inclined 
towards the screen to afford each passenger an unobstructed view. Also 
shown in FIG. 3 is the projector 22 positioned above the motion base. 
Other parameters of the preferred screen and projector combination are 
detailed herein. 
FIGS. 4-6 illustrate the assembly of the motion base 12 both in perspective 
and plan. A base frame 40 acts as a foundation for the motion base and is 
affixed to the floor or other immovable portion of the simulator system. A 
middle carriage 42 is located on a base frame upper surface 44. Along a 
bottom surface 46 of the middle carriage is a first member 48 of a first 
displacement mechanism 50 which comprises rails or tracks of a known 
design. A second member 52 cooperative with first member 48 is affixed to 
the upper surface 44 of the base frame. The middle carriage is configured 
to be moveable only along axis 54 by means of actuator 56. 
Atop the middle carriage is an upper carriage 58 having bottom surfaces 60, 
62 respectively having members 64. Cooperative rails 66 are affixed to 
respective upper surfaces 68, 70 of the middle carriage. Members 64 and 
rails 66 together comprise a second displacement mechanism 72 that 
constrains the upper carriage to movement only along a second axis 60 
perpendicular to axis 54. Actuator 74 provides force needed to move the 
upper carriage as desired. Although the displacement mechanisms are shown 
to be cooperative rails, those skilled in the art will note that other, 
equivalent means may be substituted including track or rack and pinion 
mechanisms. Similarly, other means of actuation, such as electromagnetic 
motors or pneumatic cylinders may be substituted with appropriate 
conventional modification to the system's hardware and software. 
A motion platform 76, received by the upper carriage, is preferably tilted 
at an angle-whose magnitude is in concert with a theater seat 
configuration. The motion platform comprises a lift arm 78 and stabilizer 
80 that are pivotably mounted to a passenger frame 81 to form a 
parallelogram. The lift arm is "Y" shaped and is pivotably mounted to the 
upper carriage at hinge points 82, 84. The stabilizer is preferably a 
perimeter frame structure with a cross brace 86. The passenger frame 
receives the passenger platform. Provision is made on the passenger 
platform 38 for receiving seats as well as a barrier 94 and any auxiliary 
equipment. The barrier insures the safety of the occupants as well as 
truncating any passenger view of the motion base platform. 
Actuator 88 is received at lift arm apex 90. In the preferred embodiment, 
the actuator 88 is mounted vertically and urges the lift arm upward at the 
apex. The lift arm is configured with the stabilizer to limit the motion 
of the passenger platform 38 along a vertical axis 92. 
The preferred motion base is characterized by a reduced overall height as 
compared to the prior art and by orthogonal motion in the plane containing 
the upper and middle carriages, with substantially vertical motion (i.e. 
less than 10 degrees rotation) in the third direction. The motion base 12 
has a retracted height which is much lower than conventional designs while 
retaining the extension needed for effective simulation. The inclusion of 
a reduced height motion base enables the present theater to be located 
within building constructed to a conventional ceiling height of about 14.5 
ft., and marks a point of departure of the present invention over the 
prior art. Those skilled in the art will note that other motion base 
configurations are encompassed by the present invention, including 
embodiments wherein the passenger platform is moved vertically by a rail 
or rack and pinion mechanism or by a cantilever mechanism in which the 
overall height is reduced as above. 
The motion base of the preferred embodiment is simple and light-weight to 
reduce construction and maintenance costs. The motion base members are 
configured to move only along a respective single axis such that 
rotational motions along a yaw, pitch and roll rotational axes are almost 
completely avoided. Without rotational motion, the present motion base 
obviates the need for universal joints, hinges, swivel couplings and the 
like which are needed to accomplish complex angular positions as provided 
by conventional motion bases. The present motion base is limited almost 
entirely to only three degrees of freedom, the classic x, y and z 
orthogonal axes. 
The motion base controller is preferably a proportional/integral/derivative 
(PID) type controller as is marketed by the Allen Bradley Corporation. The 
motion base controller generates actuator drive signals in response to 
command signals received from either the system controller or an external 
source such as a hard disc recorder 28 in the preferred embodiment. The 
motion base is preferably operated in closed loop fashion, with each 
actuator having a sensor 96 for generating feedback signals corresponding 
to the measured actuator displacement. These feedback signals are used by 
the motion base controller to insure a maximum error between the commanded 
position of the actuator and its actual displacement is not exceeded 
during operation. 
For a given set of audio signals and visual images in the preferred 
embodiment, a corresponding sequence of command signals must be generated 
for the motion base controller in repetitive programming situations, such 
as in an amusement ride. Typically the command signals for the motion base 
controller are programmed using an Anitech motion controller manufactured 
by the Anitech Corporation. This controller comprises algorithms which 
allow for manual selection of individual actuator displacements 
synchronized with corresponding segments of the motion picture. In 
addition, algorithms such as executed by PCFX software provided by the 
Persistence of Vision Company, Culver City, Calif. are used to provide for 
specific desired transient responses of the motion base. The PCFX program 
or its equivalent provides for enhanced editing capabilities as well as 
command signal generation utilities for sine wave generation, actuator 
displacement smoothing and key frame splicing. 
The motion base must have each programmed actuator position synchronized 
with the audio-visual images being presented to the occupants at a 
particular time. Synchronization can be accomplished in any of a number of 
ways. In the preferred embodiment, the SMPTE time code is provided to the 
system controller from the motion picture and is provided to controller 
software such as is available from the above referenced Anitech 
Corporation and auxiliary control apparatus such as a Studio 3 sequence 
and a Macintosh brand computer or equivalent. Software associated with the 
system controller synchronizes the command signals with the associated 
motion picture frame(s). The synchronized command signals are then 
preferably stored in the digital hard disc. The system controller also 
comprises software of a known type to enable synchronized playback of the 
command signals with the presentation of the motion picture to the 
occupants of the simulator system. For example, minimum acceleration is 
achieved when the command signal sequence is selected to approximate a 
Gaussian function. Similarly, other mathematical algorithms can be used to 
generate maximum acceleration. In the theater 10 this is accomplished 
using the PCFX program noted above. The speed of displacement of the 
actuator is programmed in view of the motion base controller cutoff 
frequency. 
FIG. 7 illustrates a simplified algorithm 98 executed by the present 
invention. Regardless of what kind of motion base controller provides the 
drive signals, one channel of drive signal voltage is provided to a servo 
valve on each axis which controls the amount of hydraulic pressure exerted 
by each actuator. These drive signals correspond to optimal actuator 
displacements as determined by the command signals (block 100). At 
periodic sample points, commonly four per frame or 192 per second in the 
present theater operated at 48 frames per second, the motion base 
controller polls (block 102) the associated feedback signal 104 from 
feedback sensors 96 to determine the current displacement of that 
actuator. These signals are then compared to the commanded actuator 
displacement signals at block 106 and a difference is calculated (block 
108). The result is either positive or negative and the actuator is then 
either extended or compressed in an effort to make the calculated error 
zero in response to new drive signals (block 110). 
A further advantage of the present invention results from the 
simplification in the control system needed to operate the motion base. 
The algorithms needed to generate the three axis movement as described 
herein are necessarily more complicated with motion base systems with four 
or more degrees of freedom. The combination of less complex (and bulky) 
hardware and operational software yields a substantial savings in overall 
theater costs. 
With the present theater, visual onset queues can be limited to the linear, 
orthogonal motion that characterizes the preferred motion base. Prior art 
motion bases violate this requirement, resulting in a lack of correlation 
between the visual and physical onset queues at the risk of inducing 
motion sickness. The present theater, therefore, avoids angular motion of 
that which constitutes all or some of the frame of reference of the 
passengers. In some embodiments of the present invention the passengers 
frame of reference is established by the vehicle (e.g., auto or boat) in 
which the passengers are supposedly transported. Such embodiments would 
include a motion base as detailed above along with the vehicle interior 
surrounding the passengers. The movement of the interior of the car or 
prow of the boat would be automatically restricted to exclusively 
orthogonal motion since the interior is fixed to the motion base. The 
visual images presented in conjunction with the movements of the motion 
base are unrestricted, and include angular motion, linear orthogonal 
motion and/or combinations thereof. 
However, that which comprises the frame of reference of the passengers or 
occupants can include a portion of the visual image presented on the 
screen. In general, the visual image can be divided into an image 
sub-portion which comprises part of the passengers frame of reference and 
the remainder image. This feature of the present invention marks an 
important departure from the prior art. 
The present orthogonal motion base may also be scaled in size without 
effecting the magnitude of the displacement each passenger experiences. 
This feature is a direct result of the linear orthogonal motion to which 
the present motion base is constrained. In contrast, prior art simulators 
have an upper bound on size, and hence the number of passengers. This 
constraint stems from the fact that angular motion is allowed. 
Angular motion entails rotations, usually about an axis and rarely about a 
point. Regardless, as the linear distance from the pivot increases, so 
does the magnitude of displacement and acceleration on the passengers. 
Consequently, those at or immediately about the pivot will have a reduced 
experience, while those furthest removed may be so displaced as to be 
quite uncomfortable. The only acceptable solution in the prior art is to 
limit the size of the simulator accordingly. 
The projector 22 is comprised of projection optics, a portion of which are 
shown in section in FIG. 8. The projection optics 112 preferably includes 
a "fisheye" wide angle lens 114 having a focal length of 14.8 millimeters 
to provide 180 degrees horizontal coverage with an aperture of F/2 or, for 
some applications, F/4. Collating optics 116 are also included and are 
comprised of lenses 118, 120, 122 and 124. A light gathering optical train 
126 comprised of lenses 128, 130, 132, 134, 136 as well as field lens 138 
are also provided. 
The projector itself is located in a self contained blimped pod which can 
be hung from a ceiling or attached to a wall with an appropriate bracket. 
The projector is preferably tilted to 2 degrees down from the horizontal 
and includes a 4K Xenon lamp providing 28 ft. Lamberts of light as 
measured at the center of the screen at the preferred frame rate of 48 
frames per second without film in the gate. In the theater of FIG. 1, the 
projection aperture is 1.435 in. horizontal and 0.636 in. vertical with a 
full aperture of 1.485 in. horizontal and 0.991 in. vertical, with a full 
aperture of 1.485 in. horizontal and 0.991 in. vertical. Vistavision with 
8 perforations per frame (8 perf) 35 mm film is the preferred film format. 
The projector optical train is mounted with its horizontal center line 
downward 3/16 of an in. relative to the horizontal center line of the film 
in the gate and is tilted about the forward nodal plane approximately 1 
degree down. The vertical center of the nodal plane is 13 ft. 2 in. above 
the floor in the embodiment shown in the Drawing, with the horizontal 
center of the nodal plane 5 in. in front of the screen hemisphere plane. 
The preferred screen has an interior radius of 12.5 ft., resulting in an 
interior diameter therefore of 25 ft. and exterior diameter of 26 ft. The 
equator location of the screen is 10 ft., 9 in. above the floor with a 
total vertical height of about 14.5 ft. Since the bottom plane of the 
screen is approximately 2 ft. above the floor, the preferred screen has a 
ft. cord height of 12.5 ft. The center of the image is 9 ft., 2 in. above 
the floor and the screen has a coating with a gain of plus 3. The center 
seat eye level vertical height is 8 ft. 4 in. above the ground and the 
center seat eye level horizontal position is 5 in. behind the screen 
hemisphere plane such that the center seat location is rearwardly 
displaced from the exit of the projection optics. 
A theater provided in accordance with the present invention is 
characterized by compact dimensions, especially the total height needed to 
enclose the projector as well as the screen. As noted above, conventional 
buildings are constructed to have a certain standard conventional height 
of approximately 14.5 ft. Known motion bases require buildings whose 
vertical extent is much greater due to the combination of the projection 
optics as well as the space requirements of the motion base. 
A motion base provided in accordance with the present invention is 
characterized by a retracted height which is far lower than those of known 
motion bases due, in part, to the limitation of the number of degrees of 
freedom it affords. The throw of the present motion base has not been 
compromised by the dimensions of the room in which the simulator system is 
enclosed and the full range of motion needed to accomplish the desired 
simulation is displayed by the motion base. 
The present theater is further characterized by projection optics located 
in the projector which are particularly suited to the reduced ceiling 
height. The wide angle lens used in the present invention defines two 
surfaces 140, 142 as upper and lower bounds for the image. In the present 
invention the upper surface intersects the screen at its most vertical 
extent near the ceiling while the lower surface intersects the screen at a 
line displaced below the horizon of the occupants but which is not 
substantially intersected by the occupants themselves nor motion base 
componentry, such as the barrier. In the preferred embodiment, the motion 
base platform is inclined towards the screen by a conventional amount. 
Those skilled in the art will note that the position of the projector 
relative to the screen and the motion base has been optimized to minimize 
both the vertical dimensions as well as its lateral extent, shown in FIG. 
3 as extending from left to right. Positioning of the projector further 
rearward of the motion base would be of no benefit, since a simple 
displacement would result in the illumination of the occupants as they 
would now intersect the lower boundary plane. In order to maintain the 
same visual image integrity, the projector would have to be moved upwardly 
towards (and through) the ceiling. Movement of the projector forward 
towards the screen substantially from its preferred would result in the 
projector entering the field of view of at least some of the occupants, 
greatly lessening the experience. 
Similarly, although the invention has been shown and described with respect 
to a preferred embodiment thereof, it would be understood by those skilled 
in the art that other various changes, omissions and additions thereto may 
be made without departing from the spirit and scope of the present 
invention.