1. Reading: Chapter 3 – Bowman et al. p 29 – 59.
Head-Mounted Display
Reading: Chapter 3 – Bowman et al.
p 29 – 59.
Hodges and Babu 2008

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.
Hodges and Babu 2008

3. Head-Mounted Displays
Optical System
Image Source (CRT or Flat Panel (LCD))
See–Through or Non–See–Through
Mounting Apparatus
Earphones
Tracker (Pos & Ori)
Hodges and Babu 2008

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 at the same time.
FOV may be measured horizontally, vertically or diagonally.
Hodges and Babu 2008

5. Field of View (FoV) vs. Field of Regard (FoR)
A display’s FoR refers to the amount of physical space surrounding the user in which visual images are displayed.
FoV refers to the maximum number of degrees of visual angle that can be seen instantaneously on a display.
For Instance; In a HMD, the user may have 50 degree horizontal FoV, but 360 degree FoR.
Hodges and Babu 2008

6. 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).
Hodges and Babu 2008

7. 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.
Hodges and Babu 2008

8. 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.
Hodges and Babu 2008

9. Basic Eye Cornea Crystalline Lens Fovea Optic Nerve Retina
Hodges and Babu 2008

10. The Eye
Accommodation - Term used to describe the altering of the curvature of the crystalline lens by means of the ciliary muscles. Expressed in diopters.
Retina - The sensory membrane that lines the back of the eye and receives the image formed by the lens of the eye.
Fovea - The part of the human retina that possesses the best spatial resolution or visual acuity.
Hodges and Babu 2008

11. Properties of the Eye Approximate Field of View Acuity
120 degrees vertical
150 degrees horizontal (one eye)
200 degrees horizontal (both eyes)
Acuity
30 cycles per degree (20/20 Snellen acuity).
Hodges and Babu 2008

12. Simple Formulas
Visual Resolution in Cycles per degree (Vres) = Number of pixels /2(FoV in degrees)
Example: (1024 pixels per line)/(2*40 degrees) = Horizontal resolution of 12.8 cycles per degree
To convert to Snellen acuity (as in 20/x)
Vres = 600/x (20/47)
Hodges and Babu 2008

13. Optical System
Move image to a distance that can be easily accommodated by the eye.
Magnify the image
Hodges and Babu 2008

14. Simple Magnifier HMD Designq p f
Image
Eye
Eyepiece
(one or more lenses)
Display
(Image Source)
Hodges and Babu 2008

15. Thin Lens Equation 1/p + 1/q = 1/f where
p = object distance (distance from image source to eyepiece)
q = image distance (distance of image from the lens)
f = focal length of the lens
Conventions:
If the incident light comes from the object, we say it is a real object, and define the distance from the lens to it as positive. Otherwise, it is virtual and the distance is negative.
If the emergent light goes toward the image, we say it is a real image, and define the distance from the lens to it as positive.
f = positive for a converging lens
A light ray through the center of the lens is undeflected.
Hodges and Babu 2008

16. Virtual Image
Virtual
Image
Lens
Display
Hodges and Babu 2008

17. 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
Hodges and Babu 2008

18. 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
Hodges and Babu 2008

19. Distortion in LEEP Optics
A rectangle
Maps to this
Hodges and Babu 2008

20. To correct for distortion
Must predistort image
This is a pixel-based distortion
Graphics rendering uses linear interpolation!
Too slow on most systems
Hodges and Babu 2008

21. 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?
Hodges and Babu 2008

22. Distorted FoV (cont.)
Distance along
z-axis
Hodges and Babu 2008

23. Collimated: p=f 1/p + 1/q = 1/f q = , if p=f
If the image source is placed at the focal point of the lens, then the virtual image appears at optical infinity. f
Hodges and Babu 2008

24. 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
Hodges and Babu 2008

25. 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.
Hodges and Babu 2008

26. 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
Hodges and Babu 2008

27. In Class Assignment Go to http://www.virtualresearch.com/
Figure out for the VR1280 HMD
Vertical and Horizontal Resolution
Vertical and Horizontal FoV
Vertical and Horizontal Equivalent Snellen acuity
Hodges and Babu 2008

28. OSG Tips Loading objects and adding to scene hierarchy:
osg::Node *bicycle_node = (osg::Group*)osgDB::readNodeFile("bike.obj");
bicycle_node->setName("bike");
osg::PositionAttitudeTransform* bicyclePAT = new osg::PositionAttitudeTransform;
bicyclePAT->addChild(bicycle_node);
bicyclePAT->setPosition(osg::Vec3(0.2, 0.0, 0.38)); //Position
bicyclePAT->setScale(osg::Vec3(0.0148, , ));//0.015 //Scaling
bicycle_shadow = (osg::Group*)osgDB::readNodeFile("C:/bike_shadow.obj");
bicycle_shadow->setName("bike_shadow");
bicyclePAT->addChild(bicycle_shadow); //Adding Shadow to the Bicycle object
osg::Quat quat = bicyclePAT->getAttitude(); //set rotation of the bicycle
quat.makeRotate(90.0* /180.0,osg::Matrixf::value_type(0.0f),osg::Matrixf::value_type(0.0f),osg::Matrixf::value_type(1.0f));
bicyclePAT->setAttitude(quat);
Hodges and Babu 2008

29. OSG Tips Continued… Loading objects and adding to scene hierarchy:
osg::Group *root;
root->addChild(bicyclePAT);
viewer.setSceneData(root);
Hodges and Babu 2008

30. OSG Lights Hodges and Babu 2008 // Lighting code
osg::ref_ptr<osg::Group> lightGroup (new osg::Group);
osg::ref_ptr<osg::LightSource> lightSource1 = new osg::LightSource;
//light pos
osg::Vec4f lightPos1 (osg::Vec4f( , ,1.6764,1.0f));
//light parameters
osg::ref_ptr<osg::Light> myLight1 = new osg::Light;
myLight1->setLightNum(1);
myLight1->setPosition(lightPos1);
myLight1->setAmbient(osg::Vec4(0.5f,.5f,.5f,1.0f));
myLight1->setDiffuse(osg::Vec4(.5f,.5f,.5f,1.0f));
myLight1->setConstantAttenuation(1.0f);
lightSource1->setLight(myLight1.get());
lightSource1->setLocalStateSetModes(osg::StateAttribute::ON);
lightSource1->setStateSetModes(*lightSS,osg::StateAttribute::ON);
//add to scene graph
lightGroup->addChild(lightSource1.get());
root->addChild(lightGroup.get());
Hodges and Babu 2008