1. Head-Mounted Display
Sherman & Craig, pp

2. 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

3. 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

4. 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

5. 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

6. Ocularity and IPD Ocularity Interpupillary Distance (IPD)
Monocular - HMD image goes to only one eye.
Biocular - Same HMD image to both eyes.
Binocular (stereoscopic) - Different but matched images to each eye.
Interpupillary Distance (IPD)
IPD is the horizontal distance between a user's eyes.
IPD is the distance between the two optical axes in a binocular view system.
Larry F. Hodges

7. Vignetting and Eye Relief
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.
Larry F. Hodges

8. Optical System
Move image to a distance that can be easily accommodated by the eye.
Magnify the image
Larry F. Hodges

9. Simple Magnifier HMD Designo f
Image
Eye
Eyepiece
(one or more lenses)
Display
(Image Source)
Larry F. Hodges

10. Virtual Image f f Virtual Image Display Lens Larry F. Hodges History:
Wartell:
Redrew diagram correctly – I could make no sense of original diagram.
Display
Lens
Larry F. Hodges

11. 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
Larry F. Hodges

12. 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

13. Relationship between angle and screen distance
Larry F. Hodges

14. Distortion in LEEP Optics
A rectangle
Maps to this
Larry F. Hodges

15. 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

16. 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?
Larry F. Hodges

17. Distorted FoV (cont.)
Distance along
z-axis
Larry F. Hodges

18. 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
Larry F. Hodges

19. 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.
Relay Lens
Image
Intermediate
Real Image
Eyepiece
Exit
Pupil
Larry F. Hodges

20. 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

21. Virtual Research V6 HMD Display Optical
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
Larry F. Hodges

22. 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

23. 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