Virtual Reality Devices

1
Virtual Reality Devices
Non interactive Slow image update rate
Simple image Nonengaging content
and presentation No sound
Basic Screen display Low resolution image
Monoscopic image Small field of
view No head tracking No body
motion sensing No tactile feedback
Highly interactive Fast image update rate Highly
complex image Highly engaging content and
presentation Three-dimensional sound Head-mounted
display High resolution image Stereoscopic
image Full field of view Full head tracking Full
body motion sensing Full tactile feedback
Factors affecting the degree of immersion in
virtual reality
2
NCSAs CAVE

• Virtual Reality Room with stereo glasses and
  magnetic head/hand tracking
• Fully immersive using three of four walls to
  display the graphics
• Uses an SGI Power Onyx with Reality Engine 2
  software

3
VR Head-Mounted Display
4
VR Head-Mounted Display

• Limitations
• Liquid Crystal Displays (LCDs)
• pixels not as small as a CRT
• pixels not as bright as a CRT
• cannot change as quickly as a CRT
• short focal distance makes precision, high
  resolution, and rapid response even more
  essential
• Muscle receptor feedback confusion
• light rays of scene indicate distant
• eye muscles indicate very close

5
VR Head-Mounted Display

• Parallax the apparent change in position of a
  stationary object when viewed from slightly
  different positions
• A persons eyes each see a slightly different
  view of an object
• As the brain receives these two images, it
  interprets the distance to the object in terms of
  the difference in position of the object in the
  two images
• Parallax can be used to fool the brain into
  seeing images as being at various distances
  (stereoscope and 3D movies of 50s)

6
DemonstratingParallax
Pencil
Looking at a pencil aligned What is seen
using with the corner of a room
both eyes
What is seen with What is seen with right eye
covered left eye covered
7
Parallax Problems withVR Head-Mounted Displays

• Images may not be perfectly realistic, especially
  with motion images
• When the observers head moves and the eyes are
  refocused, muscle receptor feedback data does not
  correlate with visual cues
• The perspective is always that of the camera,
  never the viewers eyes
• A viewer motion feedback mechanism is needed to
  change the perspective
• This all contributes to cybersickness
  conflicting visual and muscle feedback
  information

8
VR Aural Output

• Refer to the discussion in chapter 2 regarding
  the perception of sound
• Two key factors
• Localization
• Identification
• The brain interprets differences in the signals
  it receives from the two ears in a manner
  analogous to binocular vision
• For multimedia sound to be completely realistic,
  it requires head-position sensing feedback and
  enormous computational power not practical for
  most multimedia

9
VR Input Devices
y
x
Yaw
Roll
Origin
z
Pitch
The terminology of three-dimensional motion
10
VR Position Sensing

• A point in space is defined in terms of distance
  along three mutually perpendicular axes, usually
  termed X, Y, and Z
• Motion is defined in terms of changes in
  position, which requires six parameters
• Devices that can sense and record motion are
  termed six-degrees-of-freedom (6-DOF) devices

11
VR Position Sensing

• Sensor output from a 6-DOF device can be
• continuous
• polled, or sent only upon request
• Parameters to consider in evaluating a tracking
  device
• Lag or Latency the delay between the actual
  time of the motion and when it is available as
  input data should be lt50 mSec
• Update rate Rate at which measurements are
  made should be as fast as possible
• Precision or accuracy of the measurements
• Range over which the sensors operate
• Rejection of interference

12
VR Voice Input

• Speech Recognition
• Complications due to variations in
• Pitch
• Timbre
• Volume
• Speed of Delivery
• Inflection
• Accent
• Natural language processing