TWO 3-D SENSORS FOR ENVIRONMENT MODELING AND VIRTUAL REALITY:
CALIBRATION AND MULTI-VIEW REGISTRATION
S.F. El-Hakim, J.-A.Beraldin, G. Godin, and P. Boulanger
Institute for Information Technology, National Research Council
Ottawa, Ontario, Canada
Commission V, Working Group 1
KEY WORDS: Calibration, Modeling, Registration, Graphics, Scanner, Real-time, Three-dimensional, Virtual-Reality.
ABSTRACT
Virtual environments (VEs) also known as virtual reality (VR) are increasingly being considered for industrial, medical, and
educational / training applications, to name a few. A VE provides real-time interaction with 3-D models when combined with a
display technology that gives the user immersion in the model world and direct manipulation of objects. In many of the
applications, the truthful representation of the environment and the accurate manipulation and navigation in the virtual world
are crucial. In this paper we examine the potential use of laser range cameras and digital photogrammetry in the accurate
creation of VE models of real scenes and in the tracking of the user for precise interaction with models.
I. INTRODUCTION
Virtual environments are defined as the real-time graphics
interaction with three-dimensional models, when combined
with a display technology that gives the user immersion in
the model world and direct manipulation (Bishop and Fuchs,
1992.) The technology will radically change the way people
interact with computers and allow them to act as if they were
in places they are not. Obviously, the entertainment industry
is the leading market, however many other applications do
exist. For example, training such as flight simulators,
industrial design and prototyping (Hedberg, 1996), medical
(Goble, et al, 1995), and military (Polis et al, 1995)
applications are now employing the technology. VE is
currently advancing at a very rapid pace in both research
organizations and industry. There are many useful
publications that may serve as introduction to the topic and
document the state of the technology (e.g. Adams, 1993,
Azuma, 1995, Bishop and Fuchs, 1992, Phillips-Mahoney,
1995, Sturman and Zelter, 1994, and Stevens, 1994). We
will only give a brief overview here.
1.1. Overview of VE Technology
Virtual exploring of real places and environments, either for
leisure, engineering design, simulations, or tasks in remote
hazardous environments, is more effective and useful if
geometrical relationships and dimensions in the virtual
model are accurate. Also, since in VE the rendering of images
must respond immediately to one's movements, the
relationship between the viewer's head and hands and the 3-D
environment must be continuously and accurately known.
This is also true for interacting with and manipulating
objects in that environment. The degree of accuracy of the
modeling and positioning will widely vary with
applications. Even within an application the accuracy
requirements may vary. For example, the accuracy of the
spatial location and orientation of doors and openings
through which the viewer or moving platforms will go, is
higher than other details.
Figure 1 summarizes the main components of a VE system.
First, the 3-D world has to be created. The "computer-
generated" environment can be a truthful representation of
the "real" environment if precise, well-calibrated, laser range
cameras are used to digitize the latter to create the former.
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However, for several reasons such as availability and cost,
most models are built by either using standard geometric
primitives, libraries of pre-modeled objects, or manual
digitizing of every point. Building such a model graphically
for a detailed environment takes enormous efforts and time
and may look unrealistic. On the other hand , digitizing
the environment with laser range cameras is an excellent
alternative to graphically creating the model. It saves time
and effort while providing a more realistic model. Real-world
3-D image-based VE can advantageously complement or
replace artificially created VE in many endeavors. Currently,
creating such models of the real world remains an obstacle
for this technology and is a limitation to the
implementation in a wide range of useful applications. Other
components of the VE system include the head trackers, the
image rendering engine, and the 3-D display (either head
mounted or one or more computer screen). The rate of all the
processes must be fast enough to update the display at 20 Hz
or faster.
range camera
geometric primitives
libraries of premodeled
objects
manual digitizing every
pixel
magnetic
[3mm/ 0.19]
World Model in VE T Head, Hand & ae
orid Model in rack Head, Han
mechanical
[4mm/ 0.19]
optical
[varies]
Change Images to Respond to Movement
Figure 1: The main components of a VE system
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996
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