Object-Oriented Displays: A New l j p e of Display Systems- From Immersive Display to Object-Oriented Displays Naoki KAWAKAMI, Masahiko INAMI, Dairoku SEKIGUCHI,Yasuyuki YANAGIDA, Taro MAEDA and Susumu TACH1The University of Tokyogledia3@star.t.u- to ky0.ac.N
ABSTRACTIn this paper, we propose the concept of the “Object-OrientedDisplay,” which should enable an operator to perceive andoperate a virtual object as if it were a real one.
The Object-Oriented Display (OOD) is a new type ofdisplay system in which the surfaces of the display surround theobject and not the operator. The purpose of the OOD is thepresentation of virtual objects, whereas the purpose of ordinary
display systems is the presentation of the virtual environment.
In this project, we also describe the design andimplementation of three types of object-oriented displays, (i) The
MEDIA-A (MEDIA-Ace), (ii) The MEDIA3 (MEDIA-Cube)and (iii) The MEDIA X’tal (MEDIA-Crystal).
The MEDIA-A is a type of object-oriented display that iscompact, light, and inexpensive. It consists of a single LCD
panel and a tilt sensor.
The MEDIA3 consists of four LCD panels in the shape of acubic body. A position and orientation sensor is installed in theMEDIA3. Using the MEDIA3, a virtual object is adequatelydisplayed by controlling the image displayed on each LCD panel,corresponding to the position of the operator’s head. Thus, thevirtual object appears in the MEDIA3 in its entirety. Therefore,
the operator can recognize easily and intuitively the threedimensional form and structure of the virtual object.
For the MEDIA X’tal, on the other hand, we use opticalprojection. The MEDIA X’tal solves several problems which
occur,when using ordinary display devices for the OOD.

1. INTRODUCTION
In this paper, we describe a new technology for co-creativecommunication. In co-creative communication, we must sharethe same virtual space and/or virtual object by using techniques
for computer visualization, virtual reality, augmented reality, andmixed reality. When a user operates a virtual object in the virtualspace, handling is one of the most important factors, whichenable an operator to perceive and operate the virtual object as if
it were a real one. When using traditional display systems forvirtual reality such as HMD, the operator CANNOT handle the0-7803-5731-0/99/$10.00
01999 IEEEvirtual object. Therefore, it is very difficult for the operator torecognize where the virtual object is in three-dimensional space.
Worse than anything else, the operator cannot tell whether he isholding the object or not. The cause of this problem is that, using
traditional display system, the operator can see the virtual object
but CANNOT touch it. To solve this problem, many kinds ofhaptic displays have been developed. The most important
technique for a virtual reality system with haptic feedback is thefusion between visual space and haptic space. The ideal haptic
display is the WYSIWYF (What You See Is What You Feel) [l]display. One method to accomplish a WYSIWYF display is byusing force and/or a haptic feedback device. The other method isby using a visual display device that can be handled, in otherwords, by using the display not only as visual display but also asa haptic display. The operator handles and/or operates a virtual
object by handling and/or operating the display system. We
named such a display system an “Object-Oriented Display.”
The visual display systems used in the world of virtual
reality are divided into the following three kinds.

(1) Traditional flat-displays systems, such as CRT or Screen.
(2) Display systems of the type which is looked into throughthe window of the virtual objects, such as Head-mounted
Display[2].
(3) Display systems that present a virtual environment aroundthe operator, such as CAVE[3] or CABIN[4].
The Object-Oriented Display (OOD) is a fourth type of
display system in which the surfaces of the display surround Iheobject rather than the operator. The purpose of the OOD is thepresentation of virtual objects, whereas the purpose of theprevious three types of display systems is the presentation of thevirtual environment. For example, when using CAVE or CABIN,
an operator is located inside the display system and looks at theouter virtual world through the display. On the other hand, in thecase of the OOD, an operator is located outside the displaysystem and observes the inner virtual object through the display
surface. In the next section, we will describe how to implement
the OOD.

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2. IMPLEMENTATIONIn this section, we will describe three different implementationsof the OOD. These are (9 The MEDIA-A (MEDIA-Ace), (ii)
The MEDIA3 (MEDIA-Cube) and (iii) The MEDIA X’tal(MEDIA-Crystal).

transmitter coil of the “POLHEMUS” sensor, which measuresthe 3-dimensional relative position of the receiver coil to thetransmitter coil by using a magnetic field. Then, the operator
puts on a sensor cap, which has a receiver coil. In this way, we
can obtain the relative position of the MEDIA’ to the operator’sviewpoint.

MEDIA-A
The MEDIA-A (MEDIA-Ace) is a type of object-oriented
display that is compact, light, and inexpensive (See Fig. 1). The
MEDIA-A consists of a single LCD panel with a tilt sensor, anAID converter, and a graphic engine. When the operator tilts theMEDIA-A, the angle of inclination is measured by the tilt sensor
and digitized by the A/D converter. According to the angle ofinclination, the graphic engine simulates the movement of thevirtual object under the influence of gravity and outputs theimage of the virtual object (See Fig. 2).

Fig. 3 MEDIA3 (at SIGGRAPH ’97)

Head poaitiin’hacking

Operator

Fig. 1MEDIA-AI

I

Tilt

I

Tilt

I12bit x 2ch
ItGraphic Fngine,I .

Operator.

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1Fig. 4 Block Diagram of MEDIA’PosiUon Sensor

WSC-format

Fig. 2 Block diagram of the MEDIA-A

MEDIA3The MEDIA3 (Fig. 3) [ 5 ] , which is the first implementation ofthe OOD, was presented at SIGGRAPH ’97. The MEDIA3consists of four LCD panels in the shape of a cubic body
(120mm x 160mm x 190mm, 1.5kg). A position / orientation
sensor is installed in the MEDIA3. On the top face is theThese images are synthesized in the following way. First,
we track the operator’s head position by means of POLHEMUS
sensor (60 per second / maximum, 20 par second / average) andcalculate the operator’s viewpoint. According to the obtained
viewpoint data, the 3-dimensional data of the virtual object
inside the MEDIA3, and the position of the four corners of thetop-plane LCD of the MEDIA’, the perspective view for the topplane LCD can be calculated in the following way (usingOpenGL).
Using the MEDIA’, a virtual object is adequately displayedby controlling the image displayed on each LCD panel,corresponding to the position of the operator’s head. Thus, thevirtual object appears in its entirety in the MEDIA’. Furthermore,
the MEDIA3 can display not only the surface form but also asection of the virtual object. Therefore, the operator can easilyV - 1067

and intuitively recognize the virtual object’s three-dimensional
form and structure.

MEDIA-X’tal
The MEDIA-X’tal (MEDIA Crystal), a type of OOD that uses
the technology named “X’tal Vision,” uses optical projection.
Before describing the MEDIA X’tal, we will illustrate the X’tal
Vision optical system. We developed the X’tal Vision opticalsystem to solve the occlusion contradiction problem. When weuse STHMD (See-through Head-mounted Display) to mix thevirtual and real environment, sometimes the operator sees avirtual object located behind a real object. Normally, nobody cansee an object behind another object because of occlusion. This isan occlusion contradiction problem which causes a lowering ofefficiency.
To solve the occlusion contradiction problem, we developed
the X’tal Vision optical system. The following are the three key
techniques of X’tal Vision:
1. Using an object covered by retro-reflective material as ascreen;
2.
Placing a projector into a position optically conjugatedwith the observer’s eye by using a half-mirror;
3. Making the projector’s iris as small as possible (by using apinhole)

Retro-reflectorIFig. 5 X’tal Vision optical system
inddcnt ray.

Normal Material2.
3.

The observer can handle objects of arbitrary shape, looking
at bright images projected on the surface of the object
covered by retro-reflective paint;
There is no distortion of image, regardless of the shape ofthe screen;
A large depth of focus is obtained so that the screen can belocated at any distance from the projector.

inddent ray

rttleNd cay

Mirror

Retrwreflective Material

Fig. 6 Characteristics of a retro-reflector

Each of these points provides the following advantages,respectively :1.

inddent ray
dimladWe use the X’tal Vision optical system for the MEDIA
X’tal (See Fig. 7). The MEDIA X’tal solves several problems
which occur when using ordinary display devices for the OOD.
Fig. 8 shows an overview of the MEDIA X’tal, and Fig. 9 showsa block diagram of the MEDIA X’tal.

Moreover, the combination of the above technical points
provides this system with additional merits:
The brightness of the image does not vary in spite of thechange of the distance between the projector and thescreen (1+2);
The observer’s hands correctly occlude the displayedobject (1+3);
Stereoscopic images are obtained without glasses (1+2+3).
Fig. 5 shows the principle of X’tal Vision. The projector
with a pinhole projects the image of the virtual object. The
projected image is reflected by the half-mirror on a right angle
and retro-reflected by the retro-reflective screen. Normal andretro-reflective materials differ in the following. In the case of
normal material, a ray of light incident on the surface diffuses. In
the case of retro-reflective material, an incident ray reflects asimilar angle to the angle of incidence (See Fig. 9.

Fig. 7 MEDIA X’tal (Media Crystal)V - 1068

us to get more intuitive and multilateral knowledge than whenusing a 2-D display. OODs can improve the operation of avirtual object to a greater extent than the usual display. Then,OODs are very useful to confirm shapes used in design and toshow valuable exhibits in a museum. Therefore, we think thatour device will be interesting for designers, researchers andmuseum staffs. OODs can also be a useful device for showing 3dimensional crafting and assembly processes. When using anordinary display, it is usually difficult to demonstrate how tomake a 3-dimensional structural object. However, using OODs,
this can be done easily because operator can directly compare
the real object and the CG model.
As we have already mentioned, OODs can be used as anelectric pop-up encyclopedia or a virtual museum. An operator
can even touch and handle an object which would be dangerous
or rare in the real world. Of course, additional programming willallow for more interaction between the operator and the virtualobjects. OODs have a variety of possibilities for educational
applications.
In addition, using computer networks such as the Internet,
we can share 3-dimensional objects like documents, pictures,sounds or movies. For example, we can use OODs with a WWW
browser. On a certain WWW-homepage, these are 3-dimensional
data described in VRML, DXF, or other 3-D data format. An
operator accesses this page and clicks on the object; then, the 3dimensional data are downloaded, and the 3-dimensional object
is shown by the OODs.

Projector(Smal1Iris)

HalPMirror:(One prqedor for each eye)Fig. 8 Block diagram of the MEDIA X’tal
Object Tracking Unit

Retro-reflector

Fig. 9 Method of X’tal Vision

3. RELATIONSHIP BETWEEN OODs AND
TRADITINAL DISPLAY SYSTEMS

5. CONCLUSION

OODs are display systems which surround an object. In
comparison with traditional display systems, OODs are more
conscious of the object. HMD is a display system that surrounds
the operator’s head, while CAVE or CABIN surrounds theoperator’s body. CRT, on the other hand, is located between theoperator and the object. In the case of an object-oriented display,the display encloses the object. In other words, the purposes ofOODs are the presentation of the virtual object, whereas thepurpose of traditional display systems is the presentation of thevirtual environment. OODs are duality of immersive display
systems such as CAVE or CABIN. In the case of CAVE orCABIN, an operator is located inside the display system and cansee the outer virtual world through the display. In the case ofOODs, an operator is located outside the display system and sees
the inner virtual object through the display.

4. APPLICATIONS
For the application of OODs, we suggest some examples. OODs
are very useful for museum exhibits, for visualizing engineeringor medical data such as CAD and MRI, and for communication,education and entertainment purposes. For example, we can use
OODs for the simulation of a wind-tunnel test. OODs will allow

We aim at displaying a virtual object effectively to attendees byusing the “Object-Oriented Displays”. We propose the conceptof the OODs. The MEDIA series (MEDIA-A, MEDIA3 andMEDIA X’tal) are typical examples of “object oriented display”.

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