VR Introduction for web3d

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VR Introduction(for web3d)

• Jyun-Ming Chen
• Fall 2001

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Contents

• VR Definitions
• VR Paradigms
• VR Devices

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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 ...

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VR Definitions (cont)

• a human-computer interface
• computer creates a sensory-immersing environment,
• which interactively responds to and is
  controlled by the behavior of the user
• 3 Is of VR
• interactive, immersive, imaginative

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Variations of VR

• Generally speaking, they do achieve certain
  levels of 3 Is.
• Yet, they dont look the same (and cost
  differently)

• projected reality
• augmented reality
• HUD (head-up display)
• tele-presence
• desktop VR

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Immersive VR

• an 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

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Desktop Projective VR
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Augmented VR Telepresence
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Web3D and VR

• You can think of Web3D as an inexpensive means to
  realize desktop VR
• Characteristics
• Platform the WWW browser
• Graphics performance restricted by browser
  and/or plug-in
• Cost none
• Language/software open-source and some
  proprietary

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VR Devices
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System Architecture

• reality engine
• generate desired output from the cues of input
  sensors
• for example
• input pos/orient of head
• output scene to HMD

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Position Sensors

• 6DOF (x,y,z, r,p,y)
• contact vs. non-contact
• potentiometer
• magnetic, ultrasound, radar
• absolute vs. relative

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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 envelope
• data property
• noise, interference, limitations, ...

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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

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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

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Ultrasound Sensors

• from 9 distance between speaker-microphone,
  compute the pos/orient
• c (167.6 0.6T)m/s
• each speaker activates in cycles

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Ultrasound (cont)

• pros
• cheaper
• not subject to metallic interference
• cons
• line-of-sight constraint
• lower update rate (than magnetic ones)
• background noise (bounced off surfaces)
• multiple spkr/mic possible

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Data Glove

• most intuitive way to interface with virtual
  world
• gesture human hands has a much richer vocabulary
  (than the 6 DOF)

• original goal
• Zimmerman, interested in computer music, wondered
  whether theres a way to make music by playing
  air guitar
• 1987 optical fiber Lycra glove Polhemus
  Isotrack

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Hand DOF

• most gloves handle angle flexion only

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Joint-Angle Measurement

• technology determines the price and accuracy
• optical fiber
• strain gauge
• conductive ink sensor
• mechanical devices

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HMD

• basic components
• optics focus increase fov
• screen CRT or LCD
• enclosure hold components provide occlusion
• design concerns
• ergonomics (wt. comfort)
• image quality
• tracking

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Stereo Glasses

• group viewing
• cannot afford to give everyone an HMD
• technology
• shutter glasses
• r/b glasses
• spatial multiplexing image (SMI)
• responsive workbench

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3D Sound

• important for immersive experience
• Stereo sound vs. 3D sound
• cp. DirectSound

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Human Hearing Model

• Cues for sound localization
• ITD (interaural time difference)
• IID (interaural intensity difference)

• no info of front back
• head, torso, pinna scattering

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Measuring HRTF

• HTRF (head related transfer function)
• some data commercially available

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Using HTRF

• virtual sound position should be changed
  according to head position
• Foster estimates 30-50 MIPS for each sound source
• even more expensive for reflected sounds

• convolvotron
• source position corresponding HRTF
• convolution
• D/A, then headphone
• commercial cards
• Acoustetron, Beachtron
• no. of sound sources, reverberation allowed,
  Doppler effects, ...