VR Introduction(for web3d)Jyun-Ming ChenFall 2001

ContentsVR 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 VRGenerally 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 display)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 interact within a 3-D world

Desktop & Projective VR

Augmented VR & Telepresence

Web3D and VRYou 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 Architecturereality engine generate desired

output from the cues of input sensors

for example input: pos/orient of

head output: scene to

HMD

Position Sensors6DOF (x,y,z, r,p,y)contact vs. non-contact potentiometer magnetic,

ultrasound, radarabsolute vs. relative

Sensor Parametersupdate rate

measurement per sec.latency

time delay between action & result

accuracy difference between

actual & measuredresolution

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 orthogonal 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 speed up

Ultrasound Sensorsfrom 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 interferencecons line-of-sight constraint lower update rate (than magnetic ones) background noise (bounced off surfaces)multiple spkr/mic possible

Data Glovemost intuitive way to interface with virtual worldgesture: human hands has a much richer vocabulary (than the 6 DOF)

original goal Zimmerman, interested 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 Measurementtechnology determines the price and accuracy optical fiber strain gauge conductive ink

sensor mechanical

devices

HMDbasic components

optics: focus; increase fov screen: CRT or LCD enclosure: hold components; provide occlusiondesign concerns ergonomics (wt. comfort) image quality tracking

Stereo Glassesgroup 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 + corresponding HRTF [convolution] D/A, then headphonecommercial cards Acoustetron, Beachtron no. of sound sources, reverberation allowed, Doppler effects, ...