UTILIZING VIRTUAL ENVIRONMENTS IN CONSTRUCTION PROJECTS, dokumenty, Akustyka [ Pobierz całość w formacie PDF ]
UTILIZING VIRTUAL ENVIRONMENTS IN CONSTRUCTION
PROJECTS
SUBMITTED: August 2002
REVISED: January 2003
EDITOR: Kalle Kahkonen
Lauri Savioja, Professor,
Telecommunications Software and Multimedia Laboratory, Helsinki University of Technology, Fi
Markku Mantere,
Telecommunications Software and Multimedia Laboratory, Helsinki University of Technology, Fi
email: Markku.Mantere@hut.fi
Iikka Olli,
Telecommunications Software and Multimedia Laboratory, Helsinki University of Technology, Fi
email: Iikka.Olli@hut.fi
Seppo Äyräväinen,
Telecommunications Software and Multimedia Laboratory, Helsinki University of Technology, Fi
email: Seppo.Ayravainen@hut.fi
Matti Gröhn,
Telecommunications Software and Multimedia Laboratory, Helsinki University of Technology, Fi
email: Matti.Grohn@hut.fi
Jyrki Iso-Aho
A-konsultit, Helsinki, Fi
email: jyrki.iso-aho@a-konsultit.fi
SUMMARY:
Construction projects can gain major benefits from application of virtual environments. The
virtual reality techniques help designers to communicate with each other, as well as with the decision makers
and with the end-users. In the future, the whole product model of a new building should form one virtual
building, which can be efficiently investigated utilizing virtual environments. In this article we present some
basics of virtual reality technology, and the required software and hardware components from the viewpoint of a
construction project. The main emphasis of the article is in the description of the construction project of a new
lecture hall at the Helsinki University of Technology, and how a virtual environment was utilized in that project.
KEYWORDS
: Virtual environments, virtual reality, visualization, construction project
1. INTRODUCTION
Virtual reality (VR) has been an active field of research during the past decade. The goal of VR is to mimic the
nature such that – at the best – users can’t distinguish between reality and virtual reality. Although we are still far
from the perfect illusion, quite convincing visual, aural, and haptic techniques have been developed to achieve
this ultimate goal. Despite all the research, only few practical applications of VR exist. One quite obvious
application area is architectural visualization. In a more general level, entire construction projects can gain major
benefits from utilizing VR.
1.1 A 3D product model in building design
A model of a building may be constructed merely for presentations at a VR system, but utilization of VR really
becomes a meaningful and effective part of the working process, when the idea of a product model is used in the
ITcon Vol. 8 (2003); Savioja et al., pg. 85
design process. The idea of a product model is to combine separate drawings into one virtual building. A
traditional drawing becomes merely a view to the model at a chosen moment, whereas the whole building and its
environment are included in one single product model. Everything is modeled three-dimensionally (3D), and the
model is maintained throughout the project from start to hand-over.
Among the benefits of the product model compared to traditional methods is that one can easily produce
simulations and presentations applying VR to support project decision. In addition, it provides 3D-information
for the needs of the various consultants; bills of quantities for cost control, geometric and structural properties
for the life cycle and cost analyses of project alternatives. The product model
is also a direct source of
construction documents and production 4D-planning. Utilizing VR technologies could be a natural part of the
product model working method in the future.
1.2 Objectives of this article
We have two main objectives for this article. From the architectural point of view, our goal is to describe the
possibilities opened up by virtual environments for construction projects. From the technical point of view, we
aim to present kinds of software and hardware required for successful application of a virtual environment in a
case study.
As a case study, we present results achieved in one particular construction project: the construction of a new
large lecture hall in the main building of the Helsinki University of Technology (HUT). The virtual environment
at the Telecommunications Software and Multimedia Laboratory (TML) at the HUT was actively utilized
throughout the process, from the first drafts to the opening of the new hall (Gröhn et al., 2001b).
1.3 Organization of the article
The article is organized as follows: Section 2 gives a short overview of virtual reality technologies, and the
facilities at the HUT are described in more detail. Section 3 presents the possibilities provided by VR from the
architectural point of view. The case study is presented in Section 4. The main emphasis is on the applied models
and the parties involved in the project, as well as in their mutual interaction. Section 5 concludes the article.
2. VIRTUAL REALITY TEHCNOLOGIES
VR technology is a wide topic, covering a variety of techniques and devices. In this section, we give a brief
overview of the most important factors to be taken into account when designing a VR system. The same
principles apply to the design of models to be presented with a VR system. Such models are called virtual worlds
in this article.
At the HUT we have a virtual environment called the Experimental Virtual Environment (EVE). Software and
hardware utilized in the EVE are described in this section. In terms of this article, the VR systems similar to the
EVE are called virtual environments.
2.1 Overview of virtual reality technologies
Ivan Sutherland introduced his vision of a virtual world in his article “Ultimate Display” in 1965 (Sutherland,
1965). According to him, the main challenges in the creation of a virtual world are to make it look real, sound
real, feel real, and respond realistically to user's actions. He successfully summed up the main objectives of
implementation of a VR system. It is impossible to implement a perfect one with current technology. Thus the
objective is to make the system as immersive as possible by concentrating on the most relevant issues.
2.1.1 Look real
To make a virtual world look real, it must be carefully modeled. Surface materials, small details, and lighting are
crucial in creating a realistic environment. Small movement, like trees and leaves swaying in the wind, greatly
add to the experience. Any movement in the world must obey the principles of physics to appear realistic. In
addition, the visible world should cover a large field of view, and respond realistically to the user’s movements.
The user should be able to feel the dimensions of the environment. This is typically done by presenting the view
to the virtual world stereoscopically, i.e. from a slightly different position for each eye.
ITcon Vol. 8 (2003); Savioja et al., pg. 86
Current modeling and animation software enables the creation of realistic-looking virtual worlds, which can even
be animated. Typically, these virtual worlds can be pre-rendered, and displayed in a wide screen – even
stereoscopically – to create an immersive experience. However, the view must be created in real-time when the
user is allowed to move freely in the virtual world. This requirement limits the allowed complexity of the model,
forcing modelers to concentrate on the most essential factors. Since small details and accurate lighting are
perceptually significant but computationally expensive to render in real-time, they are typically pre-rendered as
textures. For example, the lighting conditions in the surfaces of an architectural scene are often saved as textures
using a computationally intensive radiosity method.
Stereoscopic viewing requires a different image to be presented for each eye, which can be accomplished in
many ways. One method is to use a head-mounted display (HMD), which has two small displays, one for each
eye. Optionally a sensor can be attached to HMD to register the movement of the head. HMD can be used to
create an immersive environment for one user at a time. Another method is to use a spatially immersive display
(SID) – a large display with special glasses for separating the images for each eye. The glasses can be either
passive, including red/blue, red/green, and polarizing filters – or active, like LCD shutter glasses. The use of
passive glasses requires displaying two images at a time, while with active glasses, the images are displayed
alternately for each eye. The third method for displaying stereoscopic images is called autostereoscopy. It does
not require any special glasses. However, autostereoscopic methods are often otherwise restrictive; they have a
limited viewable region, small resolution, or bad image quality. Most autostereoscopic displays are quite
complex and expensive to manufacture, and their typical size is no larger than a normal television set.
2.1.2 Sound real
For an immersive VR experience, a 3D soundscape needs to be created. 3D audio enhances the sense of
presence. In addition, it can be utilized in other tasks such as localization, navigation and data presentation
(Gröhn et al., 2001a). 3D sound can be produced using either binaural or multichannel techniques. In binaural
3D sound reproduction techniques, the principle is to control the sound signal in the entrances of the listener's
ear canals as accurately as possible. For one user this requirement is in practice easiest to fulfill with headphones
using head-related transfer functions (HRTFs) (Begault, 1994, p. 52). HRTF-reproduction is the most convenient
combination with HMDs.
In a multi-user situation, loudspeakers are more convenient than headphones. One commonly employed method
for multichannel loudspeaker reproduction is vector base amplitude panning (VBAP) (Pulkki, 1997). To enable
arbitrary positioning of sound sources VBAP uses three nearest loudspeakers for one sound.
To make a virtual world sound real the acoustics of the virtual world should be simulated in real-time. In general,
the modeling is based on knowledge of sound sources, room geometry, and acoustical properties of materials
(Savioja et al., 1999).
2.1.3 Feel real
To make a virtual world feel real, the user must be able to touch virtual objects. If the user sees a virtual table or
chair, but cannot touch it, the immersion is reduced. When the user picks up a virtual ball, he should be able to
feel, whether the surface is rough or smooth, and whether the ball is soft or hard. These two cases are called
haptic and force feedback. Both of these fields are currently under active research. Haptic devices are still quite
immature, case-specific, and expensive, while force feedback is currently used even in consumer-level products
such as joysticks, steering wheels, and gamepads.
2.1.4 Respond realistically to user's actions
To respond to the user's actions realistically, the movements of his body, head, hands and feet must be tracked.
The system must be very responsive to the user’s actions, i.e. it must have a low latency, or the immersion will
suffer. The consequences of the actions of the user must obey the principles of the physics in the virtual world.
This requires, at least, detecting the collisions between the user and the virtual objects. In practice, only some
parts of the user are tracked, a noticeable latency exists in the system, and the physics model is – at best –
incomplete.
There are many techniques to track the user. The oldest technique is mechanical tracking. The body part to be
tracked is attached to a construction with sensor-fitted joints. This is an accurate and fast method, but typically
ITcon Vol. 8 (2003); Savioja et al., pg. 87
considerably hinders user’s movement. Magnetic tracking systems are currently the most commonly applied
ones. They have receivers for measuring either AC or DC magnetic field, generated by a transmitter. Magnetic
tracking systems are quite accurate, but they are subject to distortion from external electromagnetic fields. There
are also tracking systems based on optical recognition, inertia, and ultrasound. Each of these methods has its
strengths and weaknesses. Also systems utilizing several of these techniques exist. These systems are called
hybrid systems.
2.1.5 The reality of current virtual reality techniques
Although the capacity of modern computer systems keeps increasing rapidly, a perfect VR system remains to be
seen. There are simply too many variables and too many sensors to connect, as well as too much computation to
be done in real-time. There are very complex and advanced systems for specific purposes, but not a single
system for fulfilling the dream of a perfect general-purpose VR system. The technology is just not there – yet.
In spite of the lack of a general-purpose system, there are several types of commercial, versatile, immersive VR
systems available. The systems range from HMDs and small virtual tables to large-scale virtual environments
and beyond. Traditionally virtual environments have been driven by expensive, high-end SGI Onyx computers,
but PC-based systems are becoming more and more popular. In either case, the high quality projectors and
screens required are quite expensive, as well as are high quality HMDs. Some manufacturers of commercial VR
systems are listed in
nd
Table 1: Some of the off-the-shelf immersive virtual reality systems manufacturers and
their web sites.
Fakespace
TAN
Mechdyne
Barco
Trimension
Table 2: Some of the high-end HMD manufacturers and their web sites.
CAE
Kaiser Electro-optics
General Reality
Interactive Imaging Systems
Virtual Research
2.2 EVE – Experimental Virtual Environment
The EVE is a virtual environment at the TML. The main principles of the EVE are the same as in the CAVE
(Cave Automatic Virtual Environment), originally presented in 1993 (Cruz-Neira et al., 1993). In the EVE, users
stand in a cube measuring 3×3×3 meters. Three of the faces of the cube have rear-projected screens.
illustrates the construction details of the EVE. In addition, we have a magnetic tracking system for tracking the
user. A wand, and two data gloves are the other devices to support user interaction in the EVE.
At the HUT we research technologies applied in virtual environments, especially human-computer interaction
and virtual acoustics. Therefore, we started to develop our own virtual environment, with one screen, in 1997. In
1998 the Computer Science Department moved into a new building, during which the EVE was extended.
Currently the EVE is running with three walls, and the floor.
ITcon Vol. 8 (2003); Savioja et al., pg. 88
  Figure 1: EVE – the virtual reality system at the HUT.
2.2.1 Graphics hardware
The main computer of the EVE is a Silicon Graphics (SGI) Onyx2 with 8 CPUs, 2 GB of memory and two
InfiniteReality graphics pipes. The capacity of each pipe is split to produce a stereoscopic image to two screens.
The images for the screens are projected with four ElectroHome Marquee 8500 LC Ultra projectors. To view the
images stereoscopically, we use Crystal Eyes CE2 shutter glasses. The operating system of the main computer is
IRIX that is a UNIX variant implemented by SGI.
2.2.2 Audio hardware
Hardware for sound reproduction in the EVE is built around a PC running Linux operating system. The
computer is used for acoustic modeling and audio signal processing. The audio output from the PC is taken from
two eight-channel ADAT interfaces connected to two eight-channel D/A converters. The current loudspeaker
system in the EVE consists of fourteen Genelec 1029 active monitoring loudspeakers. Multichannel 3D sound
reproduction is implemented with the VBAP technique. For more information on the acoustic design of the space
and the applied sound reproduction techniques see Hiipakka et al. (2001).
2.2.3 Input devices
There are multiple input devices in the EVE to support user interaction. The input is gathered from a mouse, a
keyboard, a wand, a magnetic tracker, and a pair of data gloves. The mouse and the keyboard are simply the
common input devices of the SGI computer. They are not used as input devices inside the EVE, but merely for
system control and for setting some parameters of the applications.
The magnetic tracker is an Ascension MotionStar tracker with six receiver units. It is used to measure the
position and orientation of the users head, hands and body.
ITcon Vol. 8 (2003); Savioja et al., pg. 89
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