Visually Coupled Systems Hardware and the Human Interface

1
Visually Coupled Systems Hardware and the Human
Interface

• Dean F. Kocian and H. Lee Task
• (Virtual Environment and Advanced Interface
  Design )
• (Woodrow Barfield and Thomas A. Furness III )

2
Visually Coupled System (VCS)

• Major components
• Head or helmet-mounted visual display
• Means of tracking head/eye position direction
• A source of visual information
• VCS vs. VR
• See Figure 6.5

3
Head/Helmet-Mounted Display

• Two main parts
• Optical system
• Display image source
• Understand the characteristics and limitations of
  each part ...
• Can get the quality and utility of the HMD

4
HMD optical systems (1)

• Two basic types
• The simple magnifier
• The compound microscope
• The simple magnifier
• See Figure 6.6
• FOV 2 arctan (S/(2F))
• Important characteristics
• Lens focal length, Diameter of the lens, Lens
  quality

5
HMD optical systems (2)

• Compound microscope HMD optical system
• See Figure 6.7
• Features
• Permit focussing
• long distance btw display and eye position
• Inverted image
• Problem the existence of a intermediate image
• Importance characteristics
• Eye relief, FOV-not easy to calculate

6
Categorization of HMDs

• See-through Type II
• See Figure 6.8
• Real world scene and virtual image superimposed
• Need to optical combiner luminance filter
• Applications symbology-only, overlay
  application
• Non-see-through Type I
• No optical combiner
• Applications pure virtual reality application

7
Display Image Sources

• See Figure 6.8
• Considerations
• size, weight, cost, resolution, brightness, power
  consumption, optical system requirements
• Categories
• Emissive (emitter of light) direct-view
• Combine light gen. and image gen. process
• Non-emissive projection
• Separate light gen. and image gen. process

8
HMD with Color Image Sources

• Type II (see-through type)
• Combiner (see Figure 6.8) filter
• efficient reflection of the HMD image
• efficient transmits of the ambient scene
• Monochrome or narrow-bandwidth image sources
• green, yellow-green, red
• Color? greatly complicate
• Type I (non-see-through type)
• Color generation schemes see Table 6-1

9
Performance Considerations (1)

• Empirical performance considerations for
  miniature image sources
• FOM (Figures Of Merits)
• luminance, contrast, resolution
• Luminance
• Unit candelas per meter squared, foot-Lambert
• Lambertian surfaces
• Emissive image source (O)
• Non-emissive image source (X)

10
Performance Considerations (2)

• Contrast and Contrast ration
• M ( Lmax - Lmin ) / ( Lmax - Lmin )
• Cr Lmax / Lmin ( 1M ) / ( 1-M )
• Brightness
• Emissive image source (O)
• Non-emissive image source reflection ratio
• Resolution
• Width and height pixel size
• Image quality

11
Emissive Display Image Sources (1)

• Lasers
• quite bright low power ( ? subjective
  impression )
• not safety in the retina associated optics and
  scanning
• Scanning system and laser activation reliable
• Electroluminescent(EL) display
• Low power consumption
• 640 x 512 ( 1.3 inch x 1.0 inch )
• Luminance
• Monochrome 2000 ft-L, Color 200 ft-L
• Phosphor technology

12
Emissive Display Image Sources (2)

• Field-emission display (FEDs)
• many million of micro-electron guns
• high energy efficiency, good brightness, high
  video speed, high contrast, wide viewing angle,
  low weight
• 512 x 512 ( 1.8 inch x 1.8 inch ), 5000 volts
• Miniature CRT
• Disadvantages
• front-to-back distance, high-voltage power,
  weight
• Advantages
• light conversion efficiency, resolution
  performance

13
Emissive Display Image Sources (3)

• Techniques
• See figure 6-10
• Geometry correction
• Horizontal/vertical smoothing (anti-aliasing)
• Format
• Comparison See Table 6-2
• Deflection method See figure 3.1
• Internal Structures
• phosphor/faceplate system, electron-gun, cathode,
  deflection yoke ( See figure 6-11 )

14
Emissive Display Image Sources (4)

• Phosphors
• Particulate phosphor
• many CRT manufacturing techniques
• optimize resolution, luminous efficiency,
  contrast, lift characteristics
• good adaptation to glass or fiber-optic
  faceplates
• Sputtered and single-crystal phosphor
• improvements over particulate phosphor system
• standard glass / hard glass faceplates

15
Emissive Display Image Sources (5)

• Deflection yoke
• CRT size
• HMD
• ElectroMagnetic Deflection (EMD)
• ElectroStatic Focus Lens system (ESFL)
• New alternative CRT
• Decelerator Pre-focus Lens (DPFL) gun
• In the future
• optimum electron-gun, phosphors technology

16
Non-emissive Disp. Img. Sources

• Liquid Crystal Display
• See figure 8.2
• low voltage, but thermal sensitivity
• Usage subtractive color LCD
• See figure 6-12
• luminance modulation and chromatic-modulation
• relative performance characteristics See table
  6-5
• HMD left/rights luminance See figure 6-14
• Comparison CRT and LCD
• See figure 6-13

17
Hybrid transmissive/emissive display image sources

• Field-Sequential color images
• Transmissive light valve technology and emissive
  CRT
• Field rate 180Hz ( each R, G, B 60Hz)
• Color filter wheel in front of CRT
• Disadvantage
• rapid eye movement color break-up
• Systems
• Kaiser Electro-Optics SIM-EYE HMD
• See figure A7 and A8

18
Helmet/Head Tracking Systems

• HMT ( Head/Helmet-Mounted Tracker)
• Position and Orientation Tracker (POT)
• Head orientation and position (HOP) information
• We want to get eye line-of-sight(LOS) information
• Transducer pairing transmitters and receivers
• Ultrasonic, magnetic, light energy

19
Basic Concepts

• Relationships
• LOS , HMT POT, HOP
• LED image source, projection, combiner
• See figure 6-16
• HMS ( Helmet-Mounted Sight) system
• Combination of HMT and sighting reticle
• Simplified representation
• See figure 6-17

20
Important Functions and Performance Criteria

• HMT POT systems
• See Table 6-7

21
LOS, Orientation, Position,

• Display information See figure 6-18
• System
• Type II ( see-through HMD )
• 6DOF - AZ, EL, Roll, X, Y, Z
• Coordinate frame See figure 6-19
• Control method
• cockpit-based overlaying the HMT LOS reticle
• system-based large area displays

22
System Head Coverage and Motion Box

• Orientation gimbal order
• Azimuth -180 180
• Elevation -90 90
• Roll -45 45
• Position operator movement
• X -6 20 inches
• Y -12 12 inches
• Z -6 6 inches
• Freeze problem out-of-motion box

23
Static Accuracy

• Operators state
• External disturbances - such as vibration
• Static accuracy angular limits for operation
• Requirements
• Static accuracy lt one-half the FOV of the sensor
• 1 2 milliradian
• Accuracy representation
• CEP circular error probability requirements
  of static accuracy
• See equation (9), page 206

24
Resolution and Repeatability

• From static accuracy performance Resolution
• Resolving capability
• Parameter representation
• 12bits 13bit. 14bit. (?)
• Example ( 12bit )
• Accuracy requirements 0.02 degree
• Azimuth spec. -180 180 degree
• Resolving capability 0.08 ( bad )
• Capability
• Repeat measurement

25
Update rate, Throughput Rate and Display Refresh
Rate

• See Figure 6-20
• Tracking device performance See figure 6-21
• free-space resolution is not fixed
• fixed scattering environments fixed resolution
• Several HMT performance See Table 6-9

26
System Interfaces and Other Issues

• System interfaces
• Tracking 1553B interface
• Display RS-422
• External clocks synchronization
• Other issues
• The number of transducers cockpit coverage
• Transducers alignment static accuracy
• External disturbances

27
System Integration

• System charateristics
• See Table 6-11
• Ocularity
• Monocular HMD image to one eye only
• Type II HMD - symbology-only
• Biocular same HMD image to both eyes
• Not stereo viewing
• Binocular matched HMD images to each eye
• Stereoscopic imagery

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System Characteristics (1)

• Color
• Monochrome
• Green CRT
• Polychrome
• more than one color, but not full color
• Color LCD, miniature CRT
• Type I or Type II
• Dependency of the real world

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System Characteristics (2)

• Monocular field of view
• Monocular FOV
• Binocular if 100 overlap, same as monocular
• Total field of view and Binocular field of view
• Total angular size of the virtual image
• In binocular, partial overlapping
• Total FOV and binocular FOV
• Horizontal / Vertical angular size

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System Characteristics (3)

• Field of regard
• Angular size of visual scene within the range of
  viewing angles
• Resolution
• Distance from center to center of the pixels
• Angular resolution human perception
• See Table 6-12. . 20/20 Snellen acuity
• Example FOV 80 degree, Display elements
  1280
• Visual resolution 8 cycles per degree ( bad )

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System Characteristics (4)

• Focus (image distance)
• Focus adjustment range
• Near-sighted and far sighted
• Range -6 diopters and 2 diopters
• Luminance
• Luminance ( measured ) and brightness ( perceived
  )
• Combiner ratio
• Ratio of transmission and reflection

32
System Characteristics (5)

• Vignetting beyond the scope
• Eye receives from some parts of display
• Exit-pupil size ( or eye-motion box ) See
  figure 6-22
• Eye motion and eye-relief distance
• Eye-relief distance
• Distance from the optical surface to the front of
  the eye
• Exit-pupil forming system and non forming system

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System Characteristics (6)

• Interpupillary distance (IPD)
• Distance btw the two optical axis 51mm 76mm
• Binocular viewing
• Distortion
• Nonlinear mapping from object space to image
  space
• Lens or display systems
• Update rate
• Frequency of recalculating image information

34
System Characteristics (7)

• Refresh rate
• Display device ( such as a CRT )
• Eye/Optics integration
• Optical system vs. human visual system
• Simple magnifier vs. compound microscope system

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System Characteristics (8)

• Eye relief versus field of view
• See figure 6-23 and equation (10)
• without vignetting ( with full FOV )
• E ( eye-motion box ) exit pupil diameter
• Relation eye box size and eye relief See figure
  6-24
• Vignetting effects See figure 6-25
• FOV and eye relief See figure 6-26 and equation
  (11) (16)

36
System Characteristics (9)

• Resolution versus field of view
• Display linear resolution ( cycles / mm )
• Visual angular resolution ( cycles per degree )
• Relation
• See equation (17) , (1) , (18) an figure 6-27
• Snellen Acuity and FOV
• See equation (19) , (20) and figure 6-28
• larger acuity number correspond to poorer
  resolution
• HMDs and Night-Vision goggles (NVGs)
• Conversion table See Table 6-13

37
System Characteristics (10)

• Focus/accommodation
• See equation (21) and figure 6-30
• d f I is infinity
• d lt f near-sighted human accommodation
• d gt f far-sighted human accommodation
• Optics/display image source interface
• See figure 6-31
• larger FOV by increasing size of the display or
  by decreasing the focal length

38
System Characteristics (11)

• Display image source/electronics interface
• Standardized helmet-vehicle interface (HVI)
• See figure 6-32 concept
• See Table 6-14 details

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Applications of VCS and VCS Components

• Military systems and applications
• Military aircaft
• HMT/D figure A1 A6, Table A1 A6
• Civilian systems and applications
• Interactive video games
• Surgery training
• Racing-car and skiers see speed
• Tele-operations deep-sea, fire, bomb, police
  surveillance
• Available HMD figure A7 A20, Table A7 A20