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, ...