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Head-Mounted Display
Sherman & Craig, pp. 151-159
Visually Coupled Systems
A system that integrates the natural visual and
motor skills of an operator into the system he is
controlling.
Basic Components
An immersive visual display (HMD, large screen
projection (CAVE), dome projection)
A means of tracking head and/or eye motion
A source of visual information that is dependent
on the user's head/eye motion.
Larry F. Hodges
Head-Mounted Displays
Optical System
Image Source (CRT or Flat Panel (LCD))
See–Through or Non–See–Through
Mounting Apparatus
Earphones
Position Tracker
Larry F. Hodges
Field of View
Monocular FOV is the angular subtense
(usually expressed in degrees) of the
displayed image as measured from the
pupil of one eye.
Total FOV is the total angular size of the displayed image
visible to both eyes.
Binocular(or stereoscopic) FOV refers to
the part of the displayed image visible to
both eyes.
FOV may be measured horizontally,
vertically or diagonally.
Larry F. Hodges
Focal Length & Diopter
Focal Length - The distance from the
surface of a lens (or mirror) at which rays
of light converge.
Diopter - The power of a lens is measured
in diopters, where the number of diopters
is equal to 1/(focal length of the lens
measured in meters).
Larry F. Hodges
Ocularity and IPD
Interpupillary
Ocularity
Distance (IPD)
Monocular - HMD image
IPD is the horizontal
goes to only one eye.
distance between a
Biocular - Same HMD
user's eyes.
image to both eyes.
Binocular (stereoscopic) IPD is the distance
between the two
- Different but matched
optical axes in a
images to each eye.
binocular view system.
Larry F. Hodges
Vignetting and Eye Relief
Vignetting
The blocking or redirecting of light rays as
they pass through the optical system.
Eye Relief Distance
Distance from the last optical surface in
the HMD optical system to the front
surface of the eye.
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Optical System
Move image to a distance that can be
easily accommodated by the eye.
Magnify the image
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Simple Magnifier HMD
Design
i
o
f
Eye
Eyepiece
(one or more lenses)
Display
(Image Source)
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Image
Virtual Image
Virtual
Image
f
f
Lens
Display
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LEEP Optics
Large Expanse Extra Perspective
Give very wide field of view for
stereoscopic images
Higher resolution (more pixels) in the
middle of the field of view, lower
resolution on the periphery
Pincushion distortion
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Fresnel Lens
A lens that has a surface consisting of a
concentric series of simple lens sections
so that a thin lens with a short focal
length and large diameter is possible
More even resolution distribution
Less distortion
Larry F. Hodges
Relationship between
angle and screen distance
80.00
60.00
50.00
Leep
40.00
Fresnel
30.00
20.00
10.00
2.
00
6.
00
10
.0
0
14
.0
0
18
.0
0
22
.0
0
26
.0
0
30
.0
0
34
.0
0
0.00
R
Distance in mm
70.00
Angle in Radians
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Distortion in LEEP Optics
A rectangle
Maps to this
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To correct for distortion
Must predistort image
This is a pixel-based
distortion
Graphics rendering
uses linear
interpolation!
Too slow on most
systems
Larry F. Hodges
Distorted Field of View
Your computational model (computer
graphics) assumes some field of view.
Scan converter may over or underscan,
not all of your graphics image may appear
on the screen.
Are the display screens aligned
perpendicular to your optical axis?
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Distorted FoV
(cont.)
Distance along
z-axis
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Collimated: o=f
1/o + 1/i = 1/f
i=
, if o=f
If the image source is placed at the focal
point of the lens, then the virtual image
appears at optical infinity.
f
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Compound Microscope
HMD Design
Relay lens produces a real image of the display image
source (screen) at some intermediate location in the
optical train. The eyepiece is then used to produce an
observable virtual image of this intermediate image.
Exit
Pupil
Intermediate
Real Image
Eyepiece
Image
Relay Lens
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Exit Pupil
The area in back of the optics from which
the entire image can be seen. Important
if IPD not adjustable, mount not secure.
Compound microscope optical systems
have a real exit pupil.
Simple magnifier optical systems do not
have an exit pupil.
Larry F. Hodges
Virtual Research V6 HMD
Display
Dual 1.3 diagonal Active Matrix Liquid Crystal
Displays
Resolution per eye: 640 x 480 (307,200 color
elements)
 Optical
Field of view: 60° diagonal
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What is the horizontal resolution
in cycles per degree?
Horizontal FoV?
Equivalent to how many RGB pixels of
horizontal resolution?
(Horizontal Resolution) / 2*Horizontal FoV
3.85 Cycles per degree or 20/156
Larry F. Hodges
Characteristics of HMDs
Immersive
You are inside the computer world
Can interact with real world (mouse,
keyboard, people)
Ergonomics
Resolution and field of view
Tethered
Larry F. Hodges