Virtual reality (VR) in education is a markedly present subject in research institutions in many countries. This paper will discuss the application of VR techniques, including the use of computer graphics and three-dimensional (3D) video production. Stereoscopy is a key point for the visualization of these applications. The system developed uses a 3D lens, a home camera, common video edition software, two low cost projectors, light polarized filters and cheap 3D eyeglasses. During the 3D video production, the aim was to evaluate all the involved process, since the elaboration of scripts, video capture and projection until the costs to build the system. This is important to demonstrate for educational institutions the advantages in adopting resources of VR for the improvement of learning.
Artigo completo em: http://periodicos.ifsc.edu.br/index.php/rtc/article/view/108
Virtual Reality: Stereoscopic Imaging for Educational Institutions
1. Conference ICBL2007 May 07 - 09, 2007 Florianopolis, Brazil
Virtual Reality: Stereoscopic Imaging for Educational Institutions
Antonio C. Amorim 1, Rodrigo D. Arnaut 2, Sérgio T. Kofuji 1, Anna H. R. Costa2
1 2
Laboratory of Integrated Systems (LSI) , Laboratory of Intelligent Techniques (LTI)
University of Sao Paulo (USP) – Sao Paulo – SP – Brazil
Key Words: Virtual reality, education, stereoscopy, 3D video, stereo vision
Abstract
Virtual reality (VR) in education is a markedly present subject in research institutions
in many countries. This paper will discuss the application of VR techniques, including
the use of computer graphics and three-dimensional (3D) video production.
Stereoscopy is a key point for the visualization of these applications. The system
developed uses a 3D lens, a home camera, common video edition software, two low
cost projectors, light polarized filters and cheap 3D eyeglasses. During the 3D video
production, the aim was to evaluate all the involved process, since the elaboration of
scripts, video capture and projection until the costs to build the system. This is
important to demonstrate for educational institutions the advantages in adopting
resources of VR for the improvement of learning.
1 Introduction
The two largest obstacles for adopting resources of Virtual Reality (VR) in educational
institutions are the high costs of equipment and the cultural barrier. The cultural barrier is an
obstacle because it is essential to have specific knowledge both for installing and operating
the equipment, as well as producing applications and contents.
Some large institutions – public or private – have technological apparatuses that make
possible to do experiments in this area. However, the lack of applications available for the
learning process makes difficult to use such systems in teaching. The applications and the
systems must be as simple as possible so that it is viable its popularization. There are some
commercial solutions, not so expensive, that offer support and specialized training for
adopting VR systems. However, they are still expensive enough to exclude the system
adoption by the great majority of the institutions that have limited budgets. Therefore, these
commercial solutions are restricted to small groups of private schools or isolated projects of
public institutions.
The largest difficulty for the popularization of VR in education consists in eliminating the
high costs and the cultural barrier simultaneously.
This study will explore the stereoscopy concepts, as well as its different techniques which has
the aim of improving the teaching and learning process in classrooms or laboratories. It is an
excellent VR tool to be used in education.
This paper also shows, through a case study, that it is possible to have a low cost system,
overcoming cultural barriers. Stereoscopy enables the students to experience a feeling of
immersion into real environments. In the case study discussed herein real videos were used
with three-dimensional (3D) projection, but it is possible to produce 3D virtual environments
with computer graphics tools, like simulations and games.
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2 Virtual Reality: devices and tools
The interest in using VR in education has grown in the last decades due to the technologies
improvement and its popularization, which allow research and development of many systems
focused in teaching and learning process [1, 3].
The VR term may have several meanings. It can be defined as a software interface that uses
virtual environment generated by a computer, in real time, providing the user with a feeling of
immersion into an artificial environment, allowing navigation in the virtual world and the
manipulation of virtual object in an intuitive way. In another meaning, a VR system can
provide images of real environments to be used with stereoscopy techniques, increasing the
spatial sensation of the user when watching with total or partial immersion. Some VR systems
use a visualization and control helmets (HMD – Head Mounted Devices), data gloves,
electronic controls (joysticks), real size projections and rooms with projection screens all over
the walls. Another possible feature is the inclusion of floor and ceiling, named Digital Cave or
IPT – Immersive Projection Theater [1]. In Brazil, the first digital cave was built in the
University of Sao Paulo (USP), by the Laboratory of Integrated Systems (LSI) of the
Polytechnic School (EPUSP). USP digital cave has five projection faces (four walls and the
floor) [4].
The VR is based on Immersion, Interaction and Involvement [2]. Immersion is the feeling of
digital presence in the virtual environment. Interaction is guaranteed by the availability of 3D
input devices to allow the user handling of virtual objects. Involvement is related to the
degree of motivation that a person shows while doing a certain activity. It may be both in
passive terms, like reading or watching a video, and active, where interaction and
manipulation of objects in the virtual environment occurs. A good example of this use is the
tools for education available in the areas of biology and geography based on interactive 3D
virtual projection systems [5].
The biggest obstacles for adopting VR have not been the technological limits, but the high
costs of developing and implementing the systems. Generally, the cost of building VR
systems is high, which limits them to institutions with large budgets. The HMDs are not so
expensive, (with costs ranging from USD 1,000.00 to USD 4,000.00, at 2004 prices) [6].
However, purchasing many of them so that a large group can interact in the same application
can be impracticable. The active digital caves allow an interaction of many users. But besides
screens and projectors, each user needs to wear an active stereo shutter glasses that consist of
two Liquid Crystal Displays (LCDs). These shutter glasses work in a frequency between 120
Hz and 150 Hz in an alternate way to get the 3D effect.
The sum of all the necessary material for making a good cave exceed USD 1 million, at 2004
prices [6], restricting its acquisition to few institutions.
The recent technical advances in IT (Information Technology) equipments available in the
market – specially regarding to the performance of processors, graphics cards, high storage
capacity, projector technology, which offers reduced size equipment, low energy consumption
and bright increase – allow low cost VR systems to be used in many institutions, even in those
ones with restricted budgets for investments.
Low cost systems use PCs on free platform (Linux), public domain tools and open source
applications. They use the stereo passive technique (see description in sections 3.2 and 3.3) to
get 3D visualization. This allows not only the cost reduction and increasing of teaching and
learning concepts, but also the technological diffusion in society [3]. The estimated cost of
such systems ranges from USD 10,000.00 to USD 60,000.00, at 2004 prices [6].
An important example of this system is the Geowall project [7], which is used for the
scientific visualization of geological data. Another interesting project is the AnatomI 3D [8]:
an anatomy atlas based on VR that interactively presents 3D structures of the human body
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offering monoscopic and stereoscopic visualization. Monoscopic means that the same image
is shown to both eyes. Stereoscopic visualization has three ways: anaglyphs, polarized light or
light shutter. These stereoscopy techniques are further explained in the following topic. The
AnatomI 3D is a free platform based on public domain tools, which can integrate structures
and descriptive texts for anatomy studies. It is structured on a VirtWall [9] platform, which is
a stereoscopic projection system of simulated environments built with computer equipment.
VirtWall’s philosophy is the adoption of low cost tools and devices, which allows the
immediate use of advanced technologies by smaller institutions.
A good concept of VR applications with the aim of allowing portability between platforms is
called overlapped abstraction layers concept [10]. It includes layers for graphic hardware,
operational system, graphic library, VR packages and VR applications. Many libraries and
open source tools can be used in this application development, such as OpenGL, Open Scene
Graph (OSG), VR Juggler, Blender, VRML and ImageJ. Table 1 illustrates the concept of
overlapped abstraction layers, with the classification of some examples for each layer.
Table 1: Description of the overlapped abstraction layers with some examples of the
systems available in the market (taken from [10], modified by the inclusion of
examples)
Layer Examples
USP Digital Cave, Geowall, AnatomI
VR Applications
3D, VirtWall, Construct 3D
3D design, animation and ImageJ, Blender, 3DS Max, Shout 3D,
modeling Software Poser, Canoma, Spazz 3D, VRML
C, C++, Java, VB.NET, ASP.NET,
VR Packages Development Languages
Shockwave, Flex, Delphi, ECMAScript
Quick Development Alice 3D, World Up, Internet Space
Packages Builder and EON Studio
Graphic Library OpenGL, DirectX
Operational System Linux, Windows
Graphic Hardware Graphics Cards, VGA Cards, GPUs
3 Stereoscopy in VR
3D images visualization in VR is obtained by stereoscopy. This is a human active effect,
because it is not present in an isolated image. It is interpreted through binocular vision,
directly by the human brain [11, 12]. To recover this effect, two different images must be
generated, one for the left eye and another one for the right eye. Each image must be obtained
with slightly different capture points, causing the parallax effect. The difference between
these capture points must be similar to the one obtained with the human eyes separation.
The studied techniques of stereoscopy are: active stereo technique, obtained with the use of
LCD shutter glasses, and the passive stereo technique, obtained by anaglyphs or with light
polarization eyeglasses. These techniques are described bellow.
3.1 Active Stereo with Shutter Glasses
The active stereo technique is commonly used in digital caves. Transparent LCD eyeglasses
are used, which work as a shutter, called shutter glasses (see figure 1). The system
synchronizes the image seen by each eye with the projected image, in order to separate left
and right eye images.
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USP digital cave has 24 computers in a cluster to generate 3D images in real time. Five 3m ×
3m walls were built, as shown in figure 2 [13].
Figure 1: LCD shutter glasses for the active stereo technique (taken from [2])
Image refresh rate must be at least 120 times per second (120 Hz) so that the user does not
notice the scintillation effect, alternating 60 times per second (60 Hz) for each eye [13]. The
price of each shutter glasses is USD 500.00 and each high-speed projector start prices from
USD 10.000,00 [6]. The active stereo technique presents the best results, but it is the most
expensive.
Figure 2: Images from the USP digital cave with the active stereo technique (taken from
[13])
3.2 Passive Stereo with Anaglyphs
Anaglyphs are scenes obtained by double image – each one from a different point, printed in
two contrasting colors that produce depth illusion. It is necessary to use simple plastic
eyeglasses and the appropriate color lens for each eye (red and blue). It uses only one
projector, since the images can be overlapped by software such as ImageJ [14], free and open
source public domain software. It is the simplest and the most economic of all the VR
stereoscopy techniques, but the results are reasonable, because color loss will occur. Observe
an image created with the anaglyphic technique, in figure 3.
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Figure 3: Image with the anaglyphic technique and eyeglasses (taken from [12])
3.3 Passive Stereo with Light Polarized
In the passive stereo technique with light polarization, two common projectors are used to
create different images for the left and the right eyes. Filters with light polarization (vertical
and horizontal polarization) are placed over each projector’s lens. Every user must wear
eyeglasses with polarized lens, so that each eye can see only the corresponding image.
A polished metal projection screen (aluminized) is necessary to preserve the light
polarization, since normal screens are opaque and spread the light in different directions,
destroying the light polarization.
Figure 4: 3D projection device with light polarization (taken from [6])
The most difficult part in configuring the system is the projector alignment. It is important
that the images corners in each projector meet. However, to overlap the two images on one
screen, it is generally necessary to pile the projectors (see figure 4) and then incline them until
the projections are aligned. This results in an image with keystone effect, projecting a
trapezoidal format image instead of a rectangular one. Some projectors allow image
adjustment that can correct this effect. Without the correction the image is still acceptable, but
it loses quality and can strain the eyes of the most sensitive people after a few minutes. It is
also important to balance the intensity and the colors of both projectors, which, preferentially,
must have the same model. Difference in intensity and colors can cause a disturbing effect on
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the eyes. If the adjustment is not aligned, the user can suffer collateral effects, such as
headache and nausea, causing even faints.
The passive stereo technique with light polarization is not the less expensive, but it presents
the best cost-benefit rate when compared to the anaglyphic and active stereo techniques. Each
projector costs around USD 500.00, the aluminized screen costs about USD 50.00, the
polarized filters for the projectors is USD 25.00 and the eyeglasses cost around USD 3.00.
Considering a system for at least 50 users, two projectors are necessary, one screen, two
filters and 50 eyeglasses, totalizing an investment, only for the projection part, around USD
1,250.00 [6], 2004 prices.
4 VR in Education
The use of VR in education has drawn much attention. In 1998, Cristine Youngblut produced
for IDA (Institute for Defense Analysis) a report with over 70 projects of VR application in
education [1]. Electronic journals appeared, such as “VR in Schools”, and special editions in
journals, as Presence, from June 1999. The developed prototypes and applications were built
to specific groups (children, university students, adults, students with physical or cognitive
incapacities), covering a wide range of didactical content (science, arts and others) and
pedagogical aims (impulse to learning, instructions, training, rehabilitation and skills
development).
An experiment was conducted by Cliburn [6] with a VR system based on light polarization.
Two groups of eight students had a lecture about astronomy. One group had an interactive
tour of the solar system using a VR system. The other group had lessons in the same subject
in a lecture format. Right after, a questionnaire was given to the groups. The group that had
used the VR system got an average of 9.8, while the other got 8.9. The group that had only the
lecture got an average of ten after watching the content in VR system. Cliburn did not
consider the result as conclusive, due to the reduced number of students, but he considered it a
sample of results that can be obtained in larger studies.
VR applications in education can be used in many areas [15], like medicine, training of
anatomic structures and distance surgeries. Another area of great interest is the industry,
where applications in oil and gas exploration are studied by many professionals using 3D
models projected in VR, such as geologists, geophysicists, and reservoir engineers. Petrobras,
the biggest oil exploration and production Brazilian company, has about thirteen VR centers
spread around its units. Embraer, an important aircraft manufacturer Brazilian company, uses
a great VR room for trainings in some airplanes. Another example is in the science and
mathematics field, where students have access to 3D models for learning in physics
experiment (Newton World), chemistry (Maxwell World) and geometry (Construct3D [16])
[15].
5 Case Study
This case study assessed the stages and processes of a 3D video production since the images
acquisition, edition and projection in the classroom. For doing so, low cost equipment was
used. It is important to emphasize that some of the equipment were provided by LSI/USP.
Even with so many sources of research, it is difficult to collect detailed material about 3D
videos production. The commonly approached aspects refer to the 3D photography. The
websites www.3dstereo.com, www.stereoscopy.com and www.pokescope.com show this type
of domain in the photography field. However, at www.stereomaker.net, it is possible to find
some software examples and videos on 3D video production.
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Among the possible ways of producing 3D video, one that uses a stereoscopic special lens
will be focused here. It eliminates the necessity of using two cameras for generating the
stereoscopic images, that is, one image for the right eye and another for the left one [17].
In this process, a second special lens is used, which is composed of two LCD shutter glasses,
a prismatic beam splitter and an adjustable mirror that is connected to the camera lens. These
special lenses are synchronized by a cable to the camera, under the same frequency of the
equipment according to figure 5.
This way, when the even field of the interlaced image is being generated, the shutter hinders
the light coming from the mirror entrance and when the odd field is being generated, only this
mirror light is recorded into the tape by the camera.
The equipment also provides a convergence of the distance adjustment between the camera
and the objects through its mirrors, called parallax effect. The mirrors are placed at 2.2” (56
mm) far from each other, a slight lesser distance than the mean distance between human
pupils, which is 2.6 (66 mm)[17].
It was possible to make the stereoscopic images capture with this system, allowing a simple
process of video production, because the images remain recorded on a tape. It was used a
home video camera, with digital recording system (mini-DV) and digital output video
(firewire). For the videos editing, it was used a laptop computer with firewire interface,
enabling the capture of tape images directly from the camera to the hard disk, without quality
loss. After the scenes selection, the edited material was copied back to the tape, using the
same camera.
For the 3D video projection were used: two low cost projectors, one aluminized screen, two
polarized light filters, one 3D video decoder, and the camera for the video player.
Two 3D videos were produced on traffic education. The first one was a video, about three
minutes, showing to new drivers a sequence of activities and tools needed for a car tire
exchange. In the second production, it was used a moving car whose objective was to
demonstrate to future drivers (children) how to deal with the city traffic flow (to deviate from
other vehicles, to turn around squares, to pass obstacles and turnouts).
Figure 5: System for the production of low cost 3D videos (extracted from [19])
The first video produced could not be used for exhibition, because the convergence of the
distance adjustment between the camera and the objects adjustment was greater than needed.
It caused the excessive increasing of parallaxes effect, resulting in images too separated to get
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the stereoscopic effect. This made difficult the 3D images visualization, causing visual
discomfort to the viewers when they tried to see the images superposed by the projectors.
The second video was exhibited for two groups of 15 students. In the first class, 12 from 15
students reported some immersion feeling. In the second group, 14 students visualized 3D
scenes, as well as objects being projected outside the screen.
The fact that some students do not achieve the visualization of 3D scenes is related to
physiologic and psychological factors of each one, which will not be approached in this study.
The conclusion is that the gotten result was quite satisfactory and promising.
5.1 Investment Amounts for 3D Videos Production
Table 2 lists the materials used in this case study, investment amounts, and detailed
description of equipment and materials needed for a video with low cost stereoscopy
production to be implemented in learning institutions. In this budget neither the services nor
the place where the exhibition will take place (classroom or auditorium) were considered.
Table 2: List of equipment used for 3D videos production
Equipment/Materials Manufacturer Model Price (USD)*
Recording
3D Lens NuView SX2000 500.00
8mm Camera Sony - 450.00
AC Plugs - - 10.00
2 tapes Sony miniDV 10.00
BNC/RCA cables - - 10.00
2 batteries for the camera Sony - 60.00
Subtotal 1040.00
Edition
Laptop computer with firewire Dell Latitude 2500.00
interface
Software for video edition Adobe Premiere 6.0 350.00
Subtotal 2850.00
Exhibition
8mm Camera (for Player) Sony - 450.00
3D video decoder NuView - 575.00
BNC/RCA cables - - 15.00
Aluminized projection screen - - 300.00
Two portable projectors InFocus LP120 2500.00
Subtotal 3840.00
TOTAL INVESTMENT 7730.00
*Estimated amounts in 2006 Brazilian market.
5.2 Amounts of Expenses for 3D Videos Production
In order to present a possible reduced budget for the video production, the same service cost
with estimated prices is showed in Table 3 for the Brazilian market, which was calculated
with the experience applied for this production. The production of a 3D video with 15 minutes
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takes from 4 to 6 men/hours for field images collection, 2 men/hours for elaborating of the
script, 3 men/hours for video edition and 1 men/hour for the exhibition in classroom. Table 3
shows the costs for executing a VR project with the estimated prices for the equipments
(rents) and the services.
Table 3: List of services performed in the case study
Service/Location (daily) Price (USD)*
Recording costs
Lens 3D NuView SX2000 75.00
Camera 8mm with parts and cables 50.00
Cameramen / team per diem 75.00
Material for settings and others 75.00
Subtotal 350.00
Edition costs
PC for video edition 100.00
Editor / producer per diem 100.00
Subtotal 200.00
Exhibition costs
Projection system (Projectors, screen, 3D decoder) 150.00
Mounting technician per diem 100.00
Subtotal 250.00
TOTAL EXPENSES 800.00
*Estimated amounts in 2006 Brazilian market.
6 Conclusion
The feasibility of VR use in education is, at first sight, related to the decreasing of the
equipment costs that is occurring every year. Once the costs barrier is surpassed, it remains
the cultural one, encouraged by the lack of specialized knowledge on VR and by the small
offering of practical applications that can be used by learning institutions all over the country.
The equipment cost decrease and the alternate solutions such as 3D videos production through
the light polarization technique shall help the dissemination of VR in educational institutions
with limited budgets. In this paper, it was used the technique of passive stereoscopy with light
polarization. This presents the best cost-benefit rate for the 3D videos production.
During the production, a certain difficulty for adjusting the distance was observed, which
influences in the parallaxes effect with the 3D lens during the process of images recording.
This can cause visual discomfort to the viewer, such as the one occurred during the first
production. In the second case, we got a more accurate adjustment, increasing the viewer’s
immersion feeling into a 3D environment under total moving.
The production of 3D educational contents requires special technique, equipment and care.
In this case study, during the first exhibition, 12 of 15 students who watched the projection
related an immersion feeling. In the second exhibition, 14 students did it. The productions
carried out in this work allowed the assessment of the technique, the difficulties and
production costs. Since the results are promising, the use of low cost VR systems in learning
institutions is considered as a real possibility.
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Authors:
Antonio, Carlos O. Amorim, Master in Computer Engineering, PhD Student,
EPUSP, LSI/PSI, PAD,
158, Prof. Luciano Gualberto Avenue, trav.3, ZIP: 05508-900, São Paulo-SP-Brazil
acoamorim@pad.lsi.usp.br
Rodrigo, Dias Arnaut, Computer Engineer, Master Student,
EPUSP, LTI/PCS,
158, Prof. Luciano Gualberto Avenue, trav.3, ZIP: 05508-900, São Paulo-SP-Brazil
rodrigo.arnaut@poli.usp.br
Sérgio, Takeo Kofuji, Master and PhD in Electronics Engineering,
EPUSP, LSI/PSI, PAD,
158, Prof. Luciano Gualberto Avenue, trav.3, ZIP: 05508-900, São Paulo-SP-Brazil
sergio.kofuji@poli.usp.br
Anna, Helena Reali Costa, Master and PhD in Electronics Engineering,
EPUSP, LTI/PCS,
158, Prof. Luciano Gualberto Avenue, trav.3, ZIP: 05508-900, São Paulo-SP-Brazil
anna.reali@poli.usp.br
11(11)