the additional steps of: removing redundancy between
different views, compressing the model by representing it
by geometric primitives at different levels, prepare the
texture maps from the measured intensities. A methodology
for the creation of triangulated, texture-mapped models from
a set of range images is presented in (Soucy et al. 1996).
5. OPTICAL TRACKING
Popular tracking devices for VE, as mentioned above, have
many disadvantages. The accuracy is limited and many
systems require uncomfortable devices to be worn by the
user. Therefore, an optical tracking system, based on
photogrammetry, is proposed. Two digital cameras, each
outfitted with light source and matching filter (figure 7), are
used for the real-time measurement of the coordinates of
retroreflective targets mounted on the head and / or the hand
of the user. Since the user is moving while the images are
being acquired, CCD cameras which allow full frame
transfer (rather than the standard interlaced two fields
separated by 16.6 ms), such as digital cameras, are
recommended. Also, shuttering is required to decrease the
integration period from frame time to only 1 ms or less,
thus providing stop-action effect.
filter
laser
©
» ;
<< retroreflective
©
wavelen gth Xnm targets(o)
Figure 7: Camera-light-filter design for tracking
digital camera
A fast image processing board is used for the real-time
extraction of targets. The matching and computation of 3-D
coordinates of the targets, using photogrammetric
algorithms are described in El-Hakim and Pizzi, 1993.
6. VE FACILITY AT NRC
A facility dedicated to VE research and application has been
established at the Institute for Information Technology at
NRC. The goal is to develop a 3-D electronic visualization
test bed that will integrate technologies in the field of VE,
Real-time imaging, and 3-D range sensing in order to display
and interact with a digital model of an environment in a
realistic manner. The main objectives of the current project
are:
1- To demonstrate, in a virtual environment, the realism of
reconstruction produced from the digital model generated;
2- to help in the development of new digital modeling
scheme to improve the realism of the digital model produced;
3- to experiment and develop various devices to interact with
the virtual environment;
4- to assess the usefulness of such systems in realistic
applications; and
5- to acquire an expertise in the field of VE and 3-D
interactive graphic systems.
The facility, which is a 10 m x 6 m x 3 m (h) room, includes
the following equipment:
144
- One high speed projector, model Marquee 9500 from
Electrohome;
- One 2.25 m by 3 m rear projection screen;
- Liquid crystal glasses and a controller for large rooms;
- Two digital video camera, one PC-Pentium and two Matrox
frame grabbers;
- SGI graphic workstation- Infinite Reality; and
- Two electromagnetic trackers.
High speed
Graphic Machine
A
Communication
Controler
a 4
Hand Tracker Head Traker
Target
Computer
Projector |
V1 V2
EEE Soraan
LCD Stereo Quos
Hand Tracker
Target Operator
Head Tracker
Figure 8: The VE facility at NRC (top view)
Figure 8 shows a top view of the set up, named ViEW (Virtual
Environment Wall).
Figure 9 shows an example of model created by over 50
views taken by the autosynchronized laser range camera and
displayed by ViEW. Figure 9-a displays two of the scanned
views while the registered images forming the complete
geometric model, represented by a triangulated mesh, is
shown in figure 9-b. The model with added shading is shown
in figure 9-c.
7. CONCLUDING REMARKS
* A virtual environment, where people are immersed,
navigate, and interact, can provide ideal solutions for many
applications such as; training, design for architecture and
industrial products, medical such as planning for surgery, and
leisure and entertainment.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996
(b) Th
