vr introduction (for web3d) jyun-ming chen fall 2001
TRANSCRIPT
VR Introduction(for web3d)
Jyun-Ming ChenFall 2001
Contents
VR DefinitionsVR ParadigmsVR Devices
VR Definitions
... making systems that fool human senses... a new media for getting your hands on information ...The difference between VR and multimedia is that VR is about creation ...
The question ... [is] whether the created world is real enough for you to suspend your disbelief for a period of time ...
VR Definitions (cont)
a human-computer interfacecomputer creates a sensory-immersing environment,which interactively responds to and is controlled by the behavior of the user3 I’s of VR interactive, immersive, imaginative
Variations of VR
Generally speaking, they do achieve certain levels of 3 “I”s. Yet, they don’t look the same (and cost differently)
projected realityaugmented reality HUD (head-up displ
ay)tele-presencedesktop VR
6
Immersive VRan immersive experience in which participants:
wear tracked head-mounted displays
view stereoscopic images
listen to 3-D sounds free to explore and inter
act within a 3-D world
Desktop & Projective VR
Augmented VR & Telepresence
Web3D and VR
You can think of Web3D as an inexpensive means to realize desktop VRCharacteristics: Platform: the WWW browser Graphics performance: restricted by browser
and/or plug-in Cost: none Language/software: open-source and some
proprietary
VR Devices
System Architecture
reality engine generate desired
output from the cues of input sensors
for example input: pos/orient
of head output: scene to
HMD
Position Sensors
6DOF (x,y,z, r,p,y)contact vs. non-contact potentiometer magnetic,
ultrasound, radar
absolute vs. relative
Sensor Parameters
update rate measurement per sec.
latency time delay between
action & result
accuracy difference between
actual & measured
resolution minimal detectable
change
modes of operation streaming: sensor
send data continuously
one-shot: data sent when requested
working envelopedata property noise, interference,
limitations, ...
Magnetic Sensors 3 stationary orthogo
nal antenna, producing a low freq. field
receiver: another set of ortho. antennas
signals of receiver to determine pos/orient
hook up receiver to moving objects
Magnetic Sensors (cont)
Sensor noise conditioning
circuitry increase near the
limit of envelope accuracy
degrades near metallic objects
[calibration method]
Multiple receiver/transmitter large envelope moving objectS data transmission s
peed up
Ultrasound Sensors
from 9 distance between speaker-microphone, compute the pos/orient c = (167.6 +
0.6T)m/s each speaker
activates in cycles
Ultrasound (cont)
pros cheaper not subject to metallic interferen
cecons
line-of-sight constraint lower update rate (than magneti
c ones) background noise (bounced off s
urfaces)multiple spkr/mic possible
Data Glove
most intuitive way to interface with virtual worldgesture: human hands has a much richer vocabulary (than the 6 DOF)
original goal Zimmerman, intere
sted in computer music, wondered whether there’s a way to make music by playing air guitar
1987: optical fiber + Lycra glove + Polhemus Isotrack
most gloves handle angle flexion only
Hand DOF
Joint-Angle Measurement
technology determines the price and accuracy optical fiber strain gauge conductive ink
sensor mechanical
devices
HMD
basic components optics: focus; increase f
ov screen: CRT or LCD enclosure: hold compon
ents; provide occlusiondesign concerns
ergonomics (wt. comfort)
image quality tracking
Stereo Glasses
group viewing cannot afford to
give everyone an HMD
technology shutter glasses r/b glasses spatial multiplexing
image (SMI) responsive
workbench
3D Sound
important for immersive experienceStereo sound vs. 3D sound[cp. DirectSound]
Human Hearing ModelCues for sound localization
ITD (interaural time difference)
IID (interaural intensity difference)
• no info of front & back– head, torso, pinna scattering
Measuring HRTF
HTRF (head related transfer function)
some data commercially available
Using HTRF
virtual sound position should be changed according to head positionFoster estimates 30-50 MIPS for each sound source even more
expensive for reflected sounds
convolvotron source position + corres
ponding HRTF [convolution] D/A, then headphone
commercial cards Acoustetron, Beachtron no. of sound sources, re
verberation allowed, Doppler effects, ...